The Immune System; Part I
Medgar Evers College, CUNY
Bio 261; Microbiology
Dr. Santos
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• Immunology
• The study of the physiological mechanisms that
humans and animals use to defend their bodies
from invasion by microorganisms.
• The immune system
• The tissues, cells, and molecules involved in
host defense mechanisms, primarily against
infectious agents.
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Infectious agents
• There are four types of infectious agents.
• Bacteria, viruses, fungi, and parasites such as
worms and protozoa.
• Anything foreign that enters your body and
activates your immune system is called an
ANTIGEN.
• Two major kinds of defense have evolved that
counter these threats
– Innate immunity and acquired immunity
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Innate Immunity
• Innate immunity
– Is present before any exposure to pathogens
and is effective from the time of birth
– Involves nonspecific responses to pathogens
Figure 43.1
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3m
Acquired Immunity
• Acquired immunity, also called adaptive
immunity
– Develops only after exposure to inducing
agents such as microbes, toxins, or other
foreign substances
– Involves a very specific response to pathogens
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Innate Immunity
7 components
1- First line of defenses such as physical
barriers, antimicrobial substances and the
normal microbiota.
2- Specialized cells and chemicals they use to
communicate with each other and the
immediate environment.
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3-Pattern recognition receptors to detect PAMP
(pathogenic associated molecular patterns).
4- The Complement system
5- Phagocytosis
6- Inflammation
7- Fever
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1-Physical barriers/chemicals
• Include the skin
• the mucous membranes
• Lysozyme, found in tears and mucus that bathe
mucous membranes, destroys bacteria.
• Sweat is high in salt and when it evaporates
leaves behind salt residues that inhibit bacterial
growth.
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• Lactoferrins and tranferrins are iron binding
proteins found in saliva, mucus and tears,
blood and tissue fluids. They bind to Iron and
doesn’t make it available for microbes.
Microbes need Iron for growth.
• Defensins are produced by neutrophils and
epithelial cells. They are short peptides that
insert into the bacterial membrane forming
pores and disrupting the integrity of the cell.
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Normal microbiota
• The normal microbiota or flora is the population of
bacteria living in your body.
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2- cells and chemicals of communication
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Granulocytes
• All granulocytes contain cytoplasmic granules
with biologically active chemicals. 3 types of
granulocytes are
• Neutrophils
• Basophils
• Eosinophils.
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Neutrophils
• Are phagocytic cells that eat and destroys foreign
material. They are specially effective against bacteria
and damaged cells.
• Neutrophils are highly active, short lived (1 to 2 days)
phagocytic cells that must be recruited to the site of
damage.
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Basophils
• Involved in allergic reactions and inflammation.
• The granules contain histamines and other chemicals
that increase capillary permeability during
inflammation.
• Mast cells are similar to them but only found in tissues.
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Eosinophils
• The granules of eosinophils stain red with the
acidic dye eosin.
• These blood cells are mainly involved in
expelling parasitic worms from the body.
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Mononuclear phagocytes (macrophages)
• They differentiate from a monocyte.
• Are present in virtually all tissues to at least
some extend.
• Are phagocytic cells.
• Can live for weeks to a few months.
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Dendritic cell
• Main scouts of the immune system. These cells
are known as antigen presenting cells.
• They survey body fluids and tissues for
potential pathogens and present the antigen to
T cells.
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Cell communication
• Cells of the Immune system must communicate
with each other and their immediate
environment in order to effectively do their job.
• They do this through surface receptors,
cytokines, and adhesion molecules.
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List of cytokines
• These are proteins secreted by blood cells to
communicate with other cells.
• They bind to cytokine receptors that are found
on cells they regulate.
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• Types of cytokines include;
1-Chemokines.
2- Colony stimulating factors
3- Interferons, INF, are important against viral
infections.
4- Interleukins
5- Tumor necrosis
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3- Pattern recognition receptors
• These pattern recognition sensor systems
allow the body to detect foreign material. They
include the Toll like receptors and NOD
proteins.
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• Toll like receptors are types of proteins that
specifically look out for foreign microbes and
help activate the Immune response.
• Both These receptors specifically look out for
peptidoglycan, flagellin, LPS, bacterial
plasmids, bacterial DNA or anything that
signals a foreign invasion.
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4- The complement system
• The complement system is a series of proteins
that circulate in the blood and the fluids that
bathe the tissues and organs.
• 3 ways to activate
• Classical (antibody-antigen)
• Alternative (C3b binding to invader)
• Lectin (Mannose binding lectin binding to
invader)
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5- Phagocytosis
• Phagocytes attach to their prey via surface receptors
– And engulf them, forming a vacuole that fuses with a
lysosome
1 Pseudopodia
surround
microbes.
Microbes
2 Microbes
are engulfed
into cell.
MACROPHAGE
3 Vacuole
containing
microbes
forms.
Vacuole
Lysosome
containing
enzymes
4 Vacuole
and lysosome
fuse.
5 Toxic
compounds
and lysosomal
enzymes
destroy microbes.
Figure 43.4
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6 Microbial
debris is
released by
exocytosis.
6- Inflammatory Response
• In local inflammation, histamine and other
chemicals released from injured cells
– Promote changes in blood vessels that allow
more fluid, more phagocytes, and antimicrobial
proteins to enter the tissues.
– The vital role of inflammation is to contain the
infection, localize the response, and restore
proper tissue function.
– Four cardinal signs are swelling, redness,
heat, pain, and a fifth is loss of function.
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7- fever
• Is a strong indicator of an infectious disease.
• They elevate body temperature and make the
internal conditions more hostile to the
pathogens.
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