Specific acquired immunity
The Immune Response
Chapter 16 and 17
Nester 4th. Ed.
Characteristics of Specific Acquired
Immunity (The Immune Response)

Recognizing self from non-self (foreign)
 Protects the body from specific non-self
organisms and substances
 It is an induced response; our body cells are
trained or taught to attack which things
 Typically a specific immune response against one
pathogen will be ineffective against a different
pathogen, sometimes even a closely related but
still different pathogen
Characteristics of Specific Acquired
Immunity (The Immune Response)

Specific immunity is acquired (not innate)
• response has memory
• also called anamnestic or secondary response
• quicker/more effective than primary at
subsequent exposures
Primary and secondary response
Lag period
10 days to 2
weeks
Figure 16.11
Specific Immunity


Also known as adaptive immunity or
acquired immunity, active or passive
Normally comes into play when innate or
non-specific immunity can't handle the
problem.
Mechanisms of the Immune Response


Two types of specific immune responses;
humoral and cell mediated
Humoral immunity
• B-lymphocytes (develop in bone marrow)
proliferate and differentiated into plasma cells
produces Y-shaped molecules called Antibodies

Cell mediated immunity
• T-lymphocytes (mature in Thymus)
• Effector T cytotoxic cells
• Effector T helper cells
Cellular
Immunity
Effector T-helper cell
Humoral
Immunity
Extracellular antigen
B cell
Activates B cells
that bind antigen
Cellular
Immunity
Effector T-helper cell
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and
differentiation
of activated B cell
Activates B cells
that bind antigen
Cellular
Immunity
Effector T-helper cell
Plasma cell
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and
differentiation
of activated B cell
Activates B cells
that bind antigen
Cellular
Immunity
Effector T-helper cell
Plasma cell
Antibody
production
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and differentiation
of activated B cell
Activates B cells
that bind antigen
Cellular
Immunity
Effector T-helper cell
Plasma cell
Antibody
production
Antibodies
bind antigen
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and differentiation
of activated B cell
Activates B cells
that bind antigen
Cellular
Immunity
Plasma cell
Antibody
production
Effector T-helper cell
Virus
Host cells routinely
present samples of
cytoplasmic proteins.
Antibodies
bind antigen
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and differentiation
of activated B cell
Activates B cells
that bind antigen
Plasma cell
Cellular
Immunity
Antibody
production
Effector T-helper cell
Stimulates effector T-cytotoxic
cells that bind antigen
Effector T-cytotoxic cell
Virus
Host cells routinely
present samples of
cytoplasmic proteins.
Antibodies
bind antigen
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and differentiation
of activated B cell
Plasma cell
Activates B cells
that bind antigen
Antibody
production
Cellular
Immunity
Antibodies
bind antigen
Effector T-helper cell
Stimulates effector T-cytotoxic
cells that bind antigen
Destroys infected host cells
Effector T-cytotoxic cell
Virus
Host cells routinely
present samples of
cytoplasmic proteins.
Those cells presenting viral
proteins or other abnormal
proteins that signify danger
are destroyed.
Humoral
Immunity
Extracellular antigen
Memory cell
+
B cell
Proliferation and differentiation
of activated B cell
Plasma cell
Activates B cells
that bind antigen
Antibodies
bind antigen
Antibody
production
Cellular
Immunity
Activated macrophage
Activates macrophages that
have engulfed antigen
Effector T-helper cell
Stimulates effector T-cytotoxic
cells that bind antigen
Destroys infected host cells
Effector T-cytotoxic cell
Virus
Host cells routinely
present samples of
cytoplasmic proteins.
Those cells presenting viral
proteins or other abnormal
proteins that signify danger
are destroyed.
Molecules involved in the Immune
Response



Antigens
Antibodies
Major Histocompatibility Complex
Molecules
Molecules involved in the Immune
Response -Antigens

Any molecule that react specifically with an
antibody or a lymphocyte.
 Foreign to the host
 Immunogens are antigens that elicit an immune
response in a given situation
 High molecular weight-at least 10,000 daltons
Molecules involved in the Immune
Response -Antigens

Complex molecules
• protein, polysaccharide - best Ag
• lipid, nucleic acid - not good at all
• lipoprotein, nucleic acid with protein average Ag
Molecules involved in the Immune
Response -Antigens

Have antigenic determinants (epitopes)
• Antibody binds to antigenic determinant small
region of antigen
• small portions of the whole antigen molecule
• equivalent of 10-25 amino acids long
• large antigens may have 100 or more epitopes
• Figure 16.1
Molecules involved in the Immune
Response -Antigens

Hapten
• Small molecules with a molecular mass under
5000 dalton make poor antigens by themselves
• Small molecules (haptens) can become
immunogenic when combined with a larger
carrier protein
• small molecular weight
• acts as an antigenic determinant
• example -penicillin (350 Dalton)
Molecules involved in the Immune
Response -Antigens

Exogenous antigens
• By inhalation, ingestion, or injection (cell wall,
flagella etc)
• E.g. dust and pollen etc.

Endogenous antigens
• Altered self antigens
• E.g. denaturation of proteins
• Addition of viral antigens to cells
• Viruses, protozoa and fungi which multiply
inside the host cells
Molecules involved in the Immune
Response - Antibodies

Immunoglobulins
• glycoproteins
• recognize epitopes of antigens
• Figure 16.1
• 5 classes - meaning types
• IgM, IgG, IgA, IgD, IgE
• Table 16.1 - Each class has a function
Antigen
binding site
Disulfide
bonds
Variable
amino
acids
Arms
Molecular weight
Stem
Crystallizable
Class of
antibody
Figure 16.3, Page 397
Molecules involved in the Immune
Response - Antibodies

Generic structure - Y
• Figure 16. 3
• Figure 16. 4
• heavy chains- constant region and variable
region
• light chains- constant region and variable
region
• hinges
• Constant region of heavy chain defines the
class of immunoglobulin
Molecules involved in the Immune
Response - Antibodies

Generic structure
• Variable regions of the light and heavy chains
together determines the specificity of antibody
to antigen
• disulfide bridges
• Fab
• Fc
• antigen binding site
Molecules involved in the Immune
Response - Antibodies
• complementarity
• Figure 16.5
• antigen binding site of antibody and specific
antigenic epitope
• Fit must be precise
• Bonds hold the antibody and antigen are
non-covalent, weak and have short range
Protective Outcome of Antibody-Antigen
Binding (Figure 16.5)


Precipitation by precipitin
Agglutination by agglutinin
Opsonization by opsoninComplement-fixation and activation
Immobilization and prevention of
adherence
Neutralization

Antibody Dependent Cellular Cytotoxicity




Toxin or virus
coated with
antibody is
prevented from
interacting with a
healthy cell
Antigen + antibod trigger
classical pathway of
complement cascasde
IgG
Multiple IgG molecules bind
to a cell, cell becomes
target for destruction by
natural killer cells
Antibodies +
antigen =
clumps for
phagocytic
cells e.g. IgM
NK cells deliver
granules containing
protease and perforin
Compliment system
C3b binds to foreign material
called opsonized, C3b called
opsonins
C3a and C5a→induce
changes in endothelial cells
and mast cells →↑ vascular
permeability
C5a attracts phagocytes
Regulatory proteins halt the
process inactivate C3b
Regulatory proteins are not
associated with microbial
surfaces
Immunoglobulin G (IgG)






Accounts for about 80% to 85% of the total
serum immunoglobulin
Is a single Y shape - 2 antigen binding sites
Is found in circulation
Is the first and most abundant circulating
class produced during the secondary
response
Reaches high levels and has a long half- life
21 days
Is part of long term immunity
Functions of IgG


Works best against infectious agents that
reach the blood
Types of reactions
•
•
•
•
•
agglutination
precipitation
neutralization
opsonization
complement fixation and activation
Functions of IgG

Crosses the placenta from the mother to
provide immunity for the new born
• (Fig 16.7)


Premature infants have a problem with
infection since they do not get this passive
transfer of immunity
Also present in colostrum
Infant antibodies
3 to 6 months
Immunoglobulin M (IgM)



Accounts for 5% to 13% of circulating
antibodies
Is the first Ab produced during primary
response to an antigen
Is made of 5 Y shapes - pentamer
• joined with a J chain and disulfide bridges
• 10 antigen binding sites
• Is found in circulation only- too big to get out
Function of IgM

good for agglutination and precipitation
• phagocytes pick up large agglutinated clumps
more efficiently



best at activating complement (classical
pathway)
removes microorganisms early in the course
of an infection
only Ab made against polysaccharide Ag’s
Immunoglobulin A (IgA)

Accounts for 10% to 13% of antibodies
 Is in monomer form in circulation
 Is in dimer form on mucous membranes called
secretory IgA (sIgA)
• Produced by plasma cells –B cells reside in the
mucosal-associated lymphoid tissue (MALT)
• Composed of two monomeric antibody subunits
connected by a J-chain
• Found on mucous membranes of genitointestinal,
genitourinary and respiratory tracts
• Found in saliva, tears and breast milk
• Ab is transported to the surface of the mucosal lining
• Secretory component helps keep enzymes from
degrading the Ab
Functions of IgA




inhibits adherence of microorganisms to
host cells
prevents colonization and therefore
infection
Neutralizes toxins and viruses
protects the breast-fed infant’s GI tract from
infection
Immunoglobulin D (IgD)




Accounts for less than 1% of all serum
immunoglobulins
Is in monomer form
Binds to B-cells by its Fc end
May be involved in the maturation of Bcells
Immunoglobulin E (IgE)





Is in monomer form
Barely detectable in blood
Bound to mast cells and basophils by its Fc
end
Is not free in circulation
Bound cells releases a mixture of potent
chemicals histamine, cytokines etc that
contributes to inflammatory response
Functions of IgE

IgE has beneficial effects.
• IgE binds to parasitic worms
• they are then expelled from the GI tract
• IgE is the second line of defense at mucous
membranes
• if org. gets past the IgA in the surface, IgE gets it in
the tissue
Functions of IgE

IgE has beneficial effects.
• IgE and IgG function in ADCC
• antibody dependent cellular cytotoxicity
• eosinophils bind IgE and IgG by their Fc
fragments
• the Ab variable ends bind to the parasites
• eosinophils release anti-microbial proteins
• eosinophils have a peroxidase-halide antimicrobial system
Major Histocompatibility Complex
Molecules




Major histocompatibility antigens
First time in humans these antigens were
identified on leukocytes and were named
human leukocyte antigens (HLA)
Major histocompatability complex (MHC)
clusters of genes
In humans MHC is located on each copy of
chromosome 6
Major Histocompatibility Complex
Molecules



Major Histocompatibility Complex (MHC)
is a set of molecules displayed on cell
surfaces that are responsible for lymphocyte
recognition and “antigen presentation”
MHC molecules control the immune
response through recognition of "self" and
"non-self" and, consequently, serve as
targets in transplantation rejection
Class I and Class II MHC molecules
Molecules of the Immune Response-Major
Histocompatibility Complex Molecules (Fig 16.16)

MHC class I molecules
• are on all nucleated
cells
• not on RBC’s
• interact with Ag
fragments of 8-10
amino acids long
• present Ag to Tcytotoxic lymphocytes
(CD8 cells)
(surface protein cluster of
differentiation)
• Endogenous antigens

MHC class II molecules
• are on macrophages, B
cells and dendritic cells
• interact with Ag
fragments of 12-25
amino acids long
• present Ag to T-helper
lymphocytes (CD4
cells)
• Exogenous antigens
Antigen binding groove
Endogenous
antigens
Exogenous
antigens
Molecules of the Immune ResponseMajor Histocompatibility Complex
Molecules

Cluster of genes
• on chromosome 6
• code for histocompatibility antigens
• on surfaces of many cell types
• in humans, called human leukocyte antigens (HLA)
• involved in transplant rejection

Also called the HLA gene cluster
Molecules of the Immune Response-Major
Histocompatibility Complex Molecules

Human leukocyte antigens (HLA)
• Proteins located on the surface of white blood
cells which play an important role in our body's
immune response to foreign substances
• Vary from person to person
• These antigens are also used to determine the
suitability of a match between a donor and a
recipient. Patients and potential donors have
their white blood cells tested for three antigens
- HLA-A, -B and –DR
• Each individual has two sets of these antigens,
one set inherited from each parent.
Molecules of the Immune Response-Major
Histocompatibility Complex Molecules

Other reasons for importance of MHC
molecules
• cell to cell contact needed for an immune
response
• recognition of self or foreign substance (nonself)
• accept self
• dispose of foreign material
Tissues involved in the Specific
Immune Response- Lymphoid System

Lymphatic vessels

Lymphoid tissues
Tissues involved in the Specific Immune
Response- Lymphoid Tissues

Primary Lymphoid
organs
• bone marrow
• thymus

Secondary lymphoid
organs
• Organs
•
•
•
•
adenoids
tonsils
spleen
lymph nodes
• Diffuse tissues
• MALT
• SALT
Cells Involved in the Specific
Immune Response


Macrophages
Lymphocytes
Cells Involved in the Specific
Immune Response - Macrophages


Non specific cells that are involved in the
killing of bacteria and the phagocytosis of
garbage in the tissues
In the specific immune response they are
important due to their role in the processing
and presenting of antigens to the
lymphocytes.
Cells Involved in the Specific
Immune Response - Macrophages

Antigen Processing
• To a Cytotoxic T cell
• To a Helper T cell
Cells Involved in the Specific
Immune Response - Lymphocytes

Development of Lymphocytes
Figure 15.3, Page 377
Clonal selection


Specific response of lymphocytes to an
antigen
This process gives rise to a population of
clones of the original cell ‘Clonal selection”
Clonal Selection of Lymphocytes

See Figure 16.8tp://highered.mcgrawhill.com/sites/0072919248/student_view0/c
hapter16/animations.html#
Development of Lymphocytes

Descriptive terms for lymphocytes
• Immature lymphocytes
• not fully developed their antigen specific receptors
• Naïve lymphocytes
• have antigen receptors but have not yet encountered
the antigen
• Activated lymphocytes
• have bound to antigen and have received signals
from another cell regarding danger and able to
proliferate
Development of Lymphocytes

Descriptive terms for lymphocytes
• Effector lymphocytes
• descendents of activated lymphocytes that
are armed with the ability to produce
specific cytokines, endowed with effector
functions TH and TC
• Memory lymphocytes
• long-lived descendents of activated
lymphocytes, responsible for the speed and
effectiveness of the secondary response
B lymphocytes and the Antibody
Response





Molecules on the outside of B lymphocytes
• B cell receptors (BCR), MHC Class II
molecules and MHC I molecules
Response to T-dependent antigens
Response to T-independent antigens
Characteristics of the primary immune response
Characteristics of the secondary immune
response
B cell receptor
Antigen
1) B cell receptor binds to antigen
B cell receptor
Antigen
1) B cell receptor binds to antigen
2) B cell internalizes antigen
B cell receptor
Antigen
1) B cell receptor binds to antigen
Antigen fragment presented
by MHC class II molecule
3) B cell degrades antigen
into peptide fragments,
then presents them in
the groove of MHC class II
molecules that reside
on the B-cell surface.
2) B cell internalizes antigen
B cell receptor
Antigen
1) B cell receptor binds to antigen
Antigen fragment presented
by MHC class II molecule
2) B cell internalizes antigen
T cells antigen-specific
receptors
T-cell receptor
Cytokine delivery
3) B cell degrades antigen
4) If the T-cell receptor of an effector
into peptide fragments,
T-helper cell binds to one of the
then presents them in
fragments, then cytokines are
the groove of MHC class II
delivered to the B cell, initiating
molecules that reside
the process of clonal expansion.
on the B-cell surface.
B lymphocytes and the Antibody
Response

Response to T-dependent antigens
•
•
•
•
Antigens are generally proteins
Antigen binds to a B-cell receptor
B-cell needs to respond
Before that B-cell requires confirmation by an
effector T-helper cell that antigen truly merit a
response
• B-cell begin dividing and differentiating and
finally producing antibodies
B lymphocytes and the Antibody
Response

Response to T-independent antigens
• Stimulate an antibody response by activating B cells
without the aid of effector T cells
• E.g. polysaccharides (capsules of Streptoccocus
pneumoniae and Hemophilus influenzae) that have
numerous identical evenly spaced epitopes
• Lipopolysaccharide (LPS) outer membrane of Gramnegative bacteria
• Clusters of B-cells receptors binds the antigen
simultaneously, which leads to B-cells activation
without T-helper cells
Figure 19.14, Page 476
Lipopolysaccharide also
functions as a T-independent
antigen
B lymphocytes and the Antibody
Response

Characteristics of the primary immune response
• Lag period (10 days to 2 weeks)
• Affinity maturation
• B-cells that binds to an antigen most tightly and for
longest duration are most likely to proliferate
• Class switching
• Under the direction of cytokines, some B cells
become programmed to produce antibodies other
than IgM. Most commonly switch to IgG production
• Memory cells
• Memory B cells persist in the body for years and in
sufficient numbers
B lymphocytes and the Antibody
Response

Characteristics of the secondary immune
response
• Memory B cells are responsible for swift and
effective response
• IgG immunoglobulins
• IgG antibody can circulate in body for years
allowing protection against specific antigens
B Lymphocyte and
Antibody Response

Characteristics of secondary response
• Memory cells responsible for swift effective
reaction of secondary response
• Often eliminate invaders before noticeable harm is
done
• Vaccine exploits phenomenon of immunologic
memory
• Some memory B cells will differentiate into
plasma cells
• Results in rapid production of antibodies
T-Lymphocytes

T lymphocytes
• Molecules on the outside of all T cells
-T-cell receptors TCR’s, MHC Class I
molecules
• Types of T cells
• Tc cells (cytotoxic) - CD8
• Th cells (helper) - CD4
• T memory cells
T-Lymphocytes

T lymphocytes
• T Cell Receptors (Figure 16-15)
T cell receptors, Figure 16.15, p 407
One antigen
binding site
One
One
T-Lymphocytes

Types of effector T cells
• T cytotoxic cells TC
• T helper cells TH
• T memory cells
T lymphocytes

T cytotoxic cells (Figure 16.17)
• have the CD8 molecule on its outside surface
• recognizes an antigen that is specific for the
shape of the TCR
• has to have the antigen presented to it by an
antigen presenting cell (macrophage and B cell)
in combination with a MHC class I molecule
• Release several pre-formed cytotoxins (perforin
and proteases)
• Apoptosis, apoptotic cells are quickly removed
by macrophages
T-Lymphocytes

Role of T cells different from B cells
• T cells never produce antibodies
• T cells armed with effectors that interact
directly with antigen
• T cell receptor does not react with free antigen
– Antigen must be present by APC
Antigen recognition by T cells
Figure 16.17, Page 408
T lymphocytes

T cytotoxic cells (continued)
• Recognizes antigens on the outside of the cell
• Endogenous antigens
– virus infected cells
– tumor cells
– tissue transplant cells
• Mechanisms of killing-Figure 16.18
• apoptosis triggered by TC cell cytokines
• cytokines
(b)
Virus
Virally infected "self" cell
presents peptides from
cytoplasmic proteins in the
groove of MHC class I molecules
(b)
Virus
Effector T-cytotoxic cell recognizes viral
antigens presented by infected "self" cell
Virally infected "self" cell
presents peptides from
cytoplasmic proteins in the
groove of MHC class I molecules
(b)
Virus
Effector T-cytotoxic cell recognizes viral
antigens presented by infected "self" cell
Virally infected "self" cell
presents peptides from
cytoplasmic proteins in the
groove of MHC class I molecules
Secretion of cytokines
Targeted delivery
of cytotoxins that
induce apoptosis
Virally infected "self" cell
undergoes apoptosis
Effector T-cytotoxic cell delivers preformed
cytotoxins to the infected "self" cell and produces
cytokines that allows neighboring cells to become
more vigilant against intracellular pathogens
T lymphocytes

T-helper cells (Figure 16.17)
• Have the CD4 marker on the outside
• Antigen is presented by a specialized group of
cells called antigen-presenting cells (APCs)
• APCs have MHC class II molecules (B cells,
dendritic cells and macrophages)
• Exogenous antigens
T Lymphocytes
Antigen Recognition and Response

Role of TH cells in B cell activation
• If TH cell encounters B cell bearing peptide:
MHC calls II complex
• TH cell responds by producing cytokines
• B cell is activated in response to cytokine
stimulation
• B cell proliferates and undergoes class switching
• Also drives formation of B memory cells
T Lymphocytes
Antigen Recognition and Response

Role of TH cells in macrophage activation
• Macrophages routinely engulf invading
microbes resistant to lysosomal killing
• TH cells recognize macrophage with engulfed
microbes resistant to killing
• TH cells activate macrophages by delivering
cytokines that induce more potent destructive
mechanisms
Macrophage engulfs materials
Macrophage engulfs materials
Macrophage degrades proteins in
phagosome into peptide fragments
Macrophage engulfs materials
Macrophage degrades proteins in
phagosome into peptide fragments
Peptide fragments from
engulfed material are presented
by MHC class II molecules
Macrophage engulfs materials
Macrophage degrades proteins in
phagosome into peptide fragments
Activated macrophage
T-cell receptor
•Enlarges
CD4
•Cell metabolism increases
•Lysosomes increases
•Nitric oxide potent antimicrobial
chemical
Secretion of cytokines
Targeted delivery
of cytotoxins activate
macrophage
Peptide fragments from
engulfed material are presented
by MHC class II molecules
Effector T-helper cell recognizes
a peptide being presented by the
macrophage and responds
by activating the macrophage
T lymphocytes

Effector T-helper cell
• Th1
• Antigen presented by macrophages
• Effector Th1
• Outcome
– Macrophages activation
– release wide variety of cytokines
– stimulate natural killer cells
– Increase production of monocytes in bone marrow
– Recruit macrophages at the site
– Make phagocytic cell to adhere or exist from blood
vessels
• Th2
• Antigen presented by B cells
• Active in the antibody response
T Lymphocytes

Antigen presentation by a macrophage to a
T-helper Cell (Figure 16.19)
T lymphocytes

Role of Dendritic Cells in T-Cell Activation
(Figure 16.20)
•Surface proteins
•Flashing red lights signifies danger
Activation of T cells
Figure 16.20, Page 411
Natural Killer Cells

Natural killer cells (NK cells)
• large, granular lymphocytes
• lack markers of T or B lymphocytes
• probably related to T cells
• but lack TCR’s
• lack antigenic specificity
Natural Killer Cells

Natural killer cells (NK cells)
• Antibody Dependent Cellular Cytotoxicity
(antibodies coat antigen, NK cells recognizes
target by Fc receptors)
• Release granules containing perforin and
proteases directly to the target cell
• Recognize and destroy host cells without
MHC class I molecules
Lymphocyte Development

Negative selection of Self-reactive B cells

Positive and negative selection of self
reactive T cells
Lymphocyte Development

Negative selection of Self-reactive B cells
• Process of eliminating lymphocytes including
B-cells that recognize “self” molecules
• Called clonal deletion
• Occurs in bone marrow and secondary
lymphoid organs
• Apoptosis
• Failure to eliminate such B-cells leads to
production of autoantibodies
Lymphocyte Development

Positive and negative selection of self
reactive T cells
• Positive selection
• Process that permits only those T cells that
recognize MHC molecule to some extent to
develop further
• Those T cells that show insufficient recognition fail
positive selection and are eliminated
• Negative selection
• T cells that recognize “self” peptide presented by
MHC molecules are also eliminated
Primary lymphoid organ
(bone marrow)
Immature B cells
Primary lymphoid organ
(thymus)
Immature T cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
molecules in the presence of
co-stimulatory molecules activates
Naive T-cytotoxic
naive T-cytotoxic cells.
(CD8) cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
molecules in the presence of
co-stimulatory molecules activates
Naive T-cytotoxic
naive T-cytotoxic cells.
(CD8) cells
Antigen presented by MHC Class II
molecules in the presence of
co-stimulatory molecules activates
naive T-helper cells
Naive T-helper
(CD4) cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
co-stimulatory molecules activates
effector T cell functions
Naive T-cytotoxic
naive T-cytotoxic cells.
(CD8) cells
Activation, proliferation,
Antigen presented by MHC Class II
molecules in the presence of
co-stimulatory molecules activates
naive T-helper cells
development of
Naive T-helper effector T cell functions
(CD4) cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
naive T-helper cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
naive T-helper cells
Th2 Th1
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Free antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
naive T-helper cells
Th2 Th1
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Free antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
naive T-helper cells
Th2 Th1
T-dependent antigens
Naive B cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Free antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
Activates B cells
naive T-helper cells
that present antigen
Th2 Th1
T-dependent antigens
Naive B cells
Activation, proliferation, class
switching, affinity maturation
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Dendritic cells
gather antigen
Free antigen
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
Activates B cells
naive T-helper cells
that present antigen
Th2 Th1
T-dependent antigens
Naive B cells
Activation, proliferation, class
switching, affinity maturation
Memory cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Dendritic cells
gather antigen
Free antigen
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
Activates B cells
naive T-helper cells
that present antigen
Th2 Th1
T-dependent antigens
Naive B cells
Activation, proliferation, class
switching, affinity maturation
Plasma cells produce antibody; depending
on site of infection and duration of exposure,
the class may be IgM, IgG, IgA, or IgE
Memory cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Dendritic cells
gather antigen
Free antigen
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
Activates B cells
naive T-helper cells
that present antigen
Th2 Th1
T-dependent antigens
Naive B cells
Activation, proliferation, class
switching, affinity maturation
Plasma cells produce antibody; depending
on site of infection and duration of exposure,
the class may be IgM, IgG, IgA, or IgE
Th 1 cells activate macrophages that present
antigen via MHC class II molecules; also produce
cytokines that orchestrate other responses
Memory cells
Primary lymphoid organ
(bone marrow)
Immature B cells
Mature (naive) B cells
Tissues
Travel to secondary lymphoid
tissue, developing into antigenpresenting cells; co-stimulatory
molecules are expressed if
antigen represents microbial
invasion or tissue damage.
Dendritic cells
gather antigen
Free antigen
Primary lymphoid organ
(thymus)
Immature T cells
Mature (naive) T cells
Secondary lymphoid organs
Antigen presented by MHC Class I
Activation, proliferation,
molecules in the presence of
development of
Memory
co-stimulatory molecules activates
effector T cell functions T-cytotoxic cells
Naive T-cytotoxic
naive T-cytotoxic cells.
Effector
(CD8) cells
Activation, proliferation,
T-cytotoxic cells
development of
Memory
Naive T-helper effector T cell functions
T-helper cells
Antigen presented by MHC Class II (CD4) cells
Effector
molecules in the presence of
T-helper cells
co-stimulatory molecules activates
Activates B cells
naive T-helper cells
that present antigen
Th2 Th1
T-dependent antigens
Naive B cells
Activation, proliferation, class
switching, affinity maturation
Plasma cells produce antibody; depending
on site of infection and duration of exposure,
the class may be IgM, IgG, IgA, or IgE
Th 1 cells activate macrophages that present
antigen via MHC class II molecules; also produce
cytokines that orchestrate other responses
Effector T-cytotoxic cells destroy cells
that presented antigen via MHC class I
molecules; also produce cytokines that
allow neighboring cells to become more
vigilant against intracellular pathogen.
Memory cells