eCommons@AKU
Department of Biological & Biomedical Sciences
Medical College, Pakistan
February 2012
Acanthamoeba is an evolutionary ancestor of
macrophages: A myth or reality?
Ruqaiyyah Siddiqui
Aga Khan University
Naveed Ahmed Khan
Aga Khan University
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Recommended Citation
Siddiqui, R., Khan, N. (2012). Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality?. Experimental
Parasitology, 130(2), 95-97.
Available at: http://ecommons.aku.edu/pakistan_fhs_mc_bbs/16
Experimental Parasitology 130 (2012) 95–97
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Experimental Parasitology
journal homepage: www.elsevier.com/locate/yexpr
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Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality?
Ruqaiyyah Siddiqui a, Naveed Ahmed Khan a,b,⇑
a
b
Aga Khan University, Stadium Road, Karachi, Pakistan
School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, England, UK
a r t i c l e
i n f o
Article history:
Received 26 October 2011
Received in revised form 17 November 2011
Accepted 19 November 2011
Available online 28 November 2011
Keywords:
Acanthamoeba
Evolution
Macrophages
a b s t r a c t
Given the remarkable similarities in cellular structure (morphological and ultra-structural features),
molecular motility, biochemical physiology, ability to capture prey by phagocytosis and interactions with
microbial pathogens, here we pose the question whether Acanthamoeba and macrophages are evolutionary related. This is discussed in the light of evolution and functional aspects such as the astonishing
resemblance of many bacteria to infect and multiply inside human macrophages and amoebae in analogous ways. Further debate and studies will determine if Acanthamoeba is an evolutionary ancestor of
macrophages. Is this a myth or reality?
Ó 2011 Elsevier Inc. All rights reserved.
Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Dear Editor,
Acanthamoeba and macrophages share remarkable similarities in
their cellular structure (morphological and ultra-structural features), molecular motility, biochemical physiology, ability to capture prey by phagocytosis and interactions with microbial
pathogens (Fig. 1). Is it plausible that Acanthamoeba and macrophages are evolutionary related? As opposed to higher animals that
are highly complex, protists (single-celled organisms) are considered as ‘‘simple’’ organisms but much of complexity arose early in
evolution. Amoebae are unicellular protists that separated from
the tree leading to the emergence of metazoan over a billion years
ago (Cosson and Soldati, 2008; Khan, 2009). Based on the ribosomal
RNA sequences, it is estimated that protists such as amoeba appear
near the base of eukaryotic evolution with strong similarity to fungi
and animals. A partial genome analysis of Acanthamoeba revealed
that it can eat and reproduce, crawl and phagocytose, form cysts
to wait out bad conditions, and organize itself internally much as
a human cell does (Anderson et al., 2005). The human body also includes cells that can crawl and phagocytose, such as macrophages.
Macrophage-like phagocytes occur throughout the animal
⇑ Corresponding author at: Aga Khan University, Stadium Road, Karachi, Pakistan.
Fax: +92 21 3493 4294.
E-mail address: [email protected] (N.A. Khan).
0014-4894/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.exppara.2011.11.005
kingdom, from marine sponges to insects and other lower and higher invertebrates/vertebrates (Hanington et al., 2009), suggesting a
common source, earlier in the evolution. The ability of amoebae to
distinguish between self and non-self is a pivotal one and is the root
of the immune system of many species (Janeway et al., 2001).
Recent work has shown that Acanthamoeba is the Trojan horse
of the microbial world. With no real specificity, it is known to uptake a variety of microbes including viruses (mimivirus, coxsackieviruses, adenoviruses, poliovirus, echovirus, enterovirus,
vesicular stomatitis virus etc.), bacteria (Aeromonas, Bacillus,
Bartonella, Burkholderia, Campylobacter, Chlamydophila, Coxiella,
Escherichia coli, Flavobacterium, Helicobacter, Legionella, Listeria,
Staphylococcus, Mycobacterium, Pasteurella, Prevotella, Porphyromonas, Pseudomonas, Rickettsia, Salmonella, Shigella, Vibrio, etc.),
protists (Cryptosporidium, Toxoplasma gondii) and yeast (Cryptococcus, Blastomyces, Sporothrix, Histoplasma, Streptomyces, Exophiala,
etc.) (reviewed in Khan (2009)). Conversely, macrophage literally
translates to ‘‘big eaters’’. Being phagocytic cells, they are a major
line of defence against invading microbes. The key property of
the macrophage is phagocytosis, which is shared with Acanthamoeba. Phagocytosis probably appeared early in evolution (Delves
et al., 2006), evolving first in unicellular eukaryotes.
The astonishing resemblance of many bacteria to infect and
multiply inside human macrophages and amoebae in analogous
96
R. Siddiqui, N.A. Khan / Experimental Parasitology 130 (2012) 95–97
Fig. 1. Transmission electron micrographs showing Acanthamoeba castellanii
belonging to the T4 genotype and an alveolar macrophage (taken from Khan,
N.A., 2008. Emerging Protozoan Pathogens. Taylor & Francis (Eds.), p. 384. ISBN:
978-0-415-42864-4).
ways and by using the same mechanisms at the transcriptional,
post-transcriptional and cellular levels indicates that amoebae
and human macrophages have comparable properties that allow
the bacteria to carry out their infection in both hosts. This concept
is further strengthened with the finding that Acanthamoeba resembles human macrophages in many ways, particularly in their cell
surface receptors and phagocytic activity (Yan et al., 2004). For
example, the viability and intracellular growth of Legionella pneumophila within Acanthamoeba and human macrophages is shown
to be dependent on corresponding genes including icmT, icmR,
icmQ, icmP, icmO, icmM, icmL, icmK, icmE, icmC, icmD, icmJ and icmB
(Segal and Shuman, 1999). More recent studies have shown that
the Dot/Icm type IV secretion system is required by L. pneumophila
for intracellular proliferation within human macrophages and
Acanthamoeba (Al-Khodor et al., 2008) by evading the default
endocytic pathway in both hosts (Segal and Shuman, 1999). The
Dot/Icm type IV secretion system is required for secretion of effectors to maintain integrity of the Legionella-containing phagosome.
The PmrA/PmrB two-component system of L. pneumophila that has
a global effect on gene expression is required for the intracellular
proliferation of L. pneumophila within human macrophages and
Acanthamoeba (Al-Khodor et al., 2009). At the same time, absence
of the heavy metal efflux gene island in L. pneumophila was required neither for survival nor replication inside Acanthamoeba
castellanii or human macrophages (Kim et al., 2009). Likewise,
invasion of Mycobacterium spp. into A. castellanii or macrophages
showed notable similarities at the transcriptional and post-translational level (Danelishvili et al., 2007). Such findings are being documented for a variety of pathogens and this has led to speculations
that Acanthamoeba is a training ground for microbial organisms to
become successful human and animal pathogens to evade macrophage-mediated killing (Salah et al., 2009), but whether the two
distinct hosts (Acanthamoeba and macrophages) have had an evolutionary relationship remains unknown.
Both Acanthamoeba and macrophages uptake microbes via
phagocytosis. This is an actin-dependent process involving the
polymerization of monomeric G-actin into filamentous F-actin
resulting in pseudopod formation and cell motility. To this end,
much of our understanding of the structure and function of the actin, myosin, profiling, and actin-binding proteins come from
Acanthamoeba and it has long been studied as a model eukaryotic
cell with emphasis on the actin cytoskeleton (reviewed in Khan,
2009). At the cellular-level, two convertible states of cytoplasm
are observed in Acanthamoeba and macrophages, i.e., endoplasm
and ectoplasm. Endoplasm (seen at the cell center, hence the
name) is fluid, while ectoplasm under the cell membrane is gellated and comparatively static. During active locomotion, endoplasm flows forwards. As the fluid endoplasm reaches the
‘‘hyaloplasm’’, which is a clear form of ectoplasm, the flow is diverted towards the membrane whereupon the endoplasm is gelled
to form ectoplasm. These transformations are quite clearly visible
both in human macrophages and Acanthamoeba and exhibit
remarkable similarity at the molecular level in structure, function
and biochemical regulation of phagocytosis and cellular motility.
Post-uptake, both Acanthamoeba and macrophages demonstrate a
number of similarities in oxidative metabolism. For example, both
exhibit cyanide-insensitive O2 uptake and increased O2 consumption during phagocytosis by expressing a respiratory burst like oxidase system which is responsible for stimulated O2 uptake during
phagocytosis leading to O2 formation. Thus phagocytosis in
Acanthamoeba exhibits many similarities to the macrophages
including increased cyanide-insensitive O2 uptake during phagocytosis; stoichiometric conversion of O2 to oxidants to kill ingested
bacteria; exhibiting a direct relationship between the number of
phagocytic vesicles produced per cell and the extent of oxidant
production and the presence of a b-type cytochrome in phagolysosomal membranes suggesting that the enzyme complexes
responsible for the respiratory burst in both Acanthamoeba and
macrophages are analogous which highlights a possible evolutionary relationship (reviewed in Khan, 2009). Similar to macrophages
which use an NADPH oxidase to produce bactericidal superoxide,
Acanthamoeba has a superoxide-generating NADPH oxidase
(Anderson et al., 2005). Overall, much of our understanding of
the cytoskeleton, cell motility, engulfment using pseudopodia,
invagination, phago-lysosome formation, re-cycling of membrane
and the underlying mechanisms comes from studies on Acanthamoeba (Khan, 2009). The similarities of these processes at the morphological, molecular, biochemical details and at the functionallevel are outstanding.
It may seem far-fetched to propose that Acanthamoeba may
have had an evolutionary relationship with macrophages, given
some of the dissimilarities. For example, the ability of Acanthamoeba to live freely in the environment and to differentiate into
a cyst stage under nutrient-deprived conditions is not observed
in macrophages. On the other hand, macrophages are produced
by cellular differentiation of monocytes suggesting that the underlying mechanisms may be common. Notably, Acanthamoeba exhibits increased number of mitochondria during its active trophozoite
stage as compared with the dormant cyst stage. Interestingly, previous findings suggest that an increased number of mitochondria
correlate with activation of macrophages (Cohn and Benson,
1964; Cohn et al., 1965). The availability of the Acanthamoeba genome, in addition to micro RNA profiles will lead to a more complete
understanding at the genetic level as well as its’ interaction with
other microbes. These studies will shed light on the possible evolutionary relationship between macrophages and Acanthamoeba and
whether this is a myth, or reality.
Acknowledgments
The authors declare (1) no conflicts of interests for the submitted work; (2) no financial relationships with commercial entities
that might have an interest in the submitted work; (3) no spouses,
partners, or children with relationships with commercial entities
that might have an interest in the submitted work; and (4) no
non-financial interests that may be relevant to the submitted work.
References
Al-Khodor, S., Price, C.T., Habyarimana, F., Kalia, A., Abu Kwaik, Y., 2008. A Dot/Icmtranslocated ankyrin protein of Legionella pneumophila is required for
intracellular proliferation within human macrophages and protozoa.
Molecular Microbiology 70 (4), 908–923.
Al-Khodor, S., Kalachikov, S., Morozova, I., Price, C.T., Abu Kwaik, Y., 2009. The PmrA/
PmrB two-component system of Legionella pneumophila is a global regulator
R. Siddiqui, N.A. Khan / Experimental Parasitology 130 (2012) 95–97
required for intracellular replication within macrophages and protozoa.
Infection and Immunity 77 (1), 374–386.
Anderson, I.J., Watkins, R.F., Samuelson, J., Spencer, D.F., Majoros, W.H., Gray, M.W.,
Loftus, B.J., 2005. Gene discovery in the Acanthamoeba castellanii genome.
Protist 156 (2), 203–214.
Cohn, Z.A., Benson, B., 1964. The differentiation of mononuclear phagocytes:
morphology, cytochemistry and biochemistry. Journal of Experimental
Medicine 121, 153–169.
Cohn, Z.A., Hirsch, J.G., Fedorko, M.E., 1965. The in vitro differentiation of
mononuclear phagocytes. IV. The ultrastructure of macrophage differentiation
in the peritoneal cavity and in culture. Journal of Experimental Medicine 123,
747–755.
Cosson, P., Soldati, T., 2008. Eat, kill or die: when amoeba meets bacteria. Current
Opinion in Microbiology 11 (3), 271–276.
Danelishvili, L., Wu, M., Stang, B., Harriff, M., Cirillo, S.L., Cirillo, J.D., Bildfell, R.,
Arbogast, B., Bermudez, L.E., 2007. Identification of Mycobacterium avium
pathogenicity island important for macrophage and amoeba infection.
Proceedings of the National Academy of Science USA 104 (26), 11038–11043.
Delves, P.J., Martin, S.J., Burton, D.R., Roit, I.M., 2006. Roitt’s Essential Immunology,
eleventh ed. Blackwell Publishing, ISBN1-4051-3603-0.
97
Hanington, P.C., Tam, J., Katzenback, B.A., Hitchen, S.J., Barreda, D.R., Belosevic, M.,
2009. Development of macrophages of cyprinid fish. Developmental &
Comparative Immunology 33 (4), 411–429.
Janeway, C.A.Jr., Travers, P., Walport, M., Shlomchik, M.J., 2001. Evolution of the
innate immune system. Immunobiology: The Immune System in Health and
Disease, fifth ed. Garland Science, ISBN-10: 0-8153-3642-X.
Khan, N.A., 2009. Acanthamoeba Biology and Pathogenesis, Caister Academic Press,
ISBN 978-1-904455-43-1.
Kim, E.H., Charpentier, X., Torres-Urquidy, O., McEvoy, M.M., Rensing, C., 2009. The
metal efflux island of Legionella pneumophila is not required for survival in
macrophages and amoebas. FEMS Microbiology Letters 301 (2), 164–170.
Salah, I.B., Ghigo, E., Drancourt, M., 2009. Free-living amoebae, a training field for
macrophage resistance of mycobacteria. Clinical Microbiology and Infection 15
(10), 894–905.
Segal, G., Shuman, H.A., 1999. Legionella pneumophila utilizes the same genes to
multiply within Acanthamoeba castellanii and human macrophages. Infection
and Immunity 67 (5), 2117–2124.
Yan, L., Cerny, R.L., Cirillo, J.D., 2004. Evidence that hsp90 is involved in the altered
interactions of Acanthamoeba castellanii variants with bacteria. Eukaryotic Cell 3
(3), 567–578.