Download the invertebrate immune system

Learning Objectives
• Understand basic divisions of the immune system
THE
INVERTEBRATE
IMMUNE SYSTEM
– Innate vs. Adaptive
– Humoral vs. Cellular
• Provide examples of each division
• Provide examples of how pathogens subvert or
evade the immune system
• Understand how these divisions work
independently and together
• Exploitation of immunity with immunostimulants
The Immune System:
Function
• All organisms have a natural tolerance to
infection, which varies with life stage,
physiology, stress, genetics immune
response
• Protects animals from infectious disease and
their toxic products.
• Powerful mechanisms to locate, neutralize,
and eliminate foreign cells or
macromolecules
Invertebrate Immune System
–
–
–
–
–
Innate Immunity
(non-specific)
Evolutionarily old
system
First line of defense
Rapid response
Distinguishes broad
classes of pathogen
No long-term memory
Potential for (Quasi-)Adaptive
Immunity
(Acquired/ Specific)
– Apparent specific
response to previously
encountered foreign
antigen
– Hypervariable and/or
alternate
histocompatibility
complex (fusion gene Fu)
– Ig Superfamily
– Not well understood
Immune System in Action
Fig 1. Litman et al. 2005
Nat Rev Immunol. Nov
2005; 5(11): 866–879.
doi: 10.1038/nri1712
Pathogen Invades/ Breaches Barriers
RECONSTRUCTING
IMMUNE PHYLOGENY:
NEW PERSPECTIVES
Signals Quasiadaptive immune
response???
Innate immune
system responds
(phagocytosis)
Eliminates
Contains
Or does not contain
1
Immune Organs
• External
• Internal Lymphoid Organs
Pathogen Invades/ Breaches Barriers
– Exoskeleton*
– Epithelium*
– Lymphoid organ
(crustaceans)
– Connective tissue or other
• Gills
tissue suspected to be
• Gut
Mucus cell: Mucus contains humoral factors source of hemocytes
(=hematopoietic tissue)
– Hemocytes
Mantle Epithelium
– Hemolymph
What happens when a
pathogen breaches the
outside barriers?
Innate immune
system responds
Lymphoid Organ
Innate Humoral Factors
Cellular and Humoral
Effector Molecules
Innate
Cellular
• Substances that non-specifically inhibit or
destroy pathogens
• Found in hemolymph, mucus, hemocytes
and other tissues
Adaptive
Humoral
Cellular ?
Humoral?
• Cellular: mediated by cells
• Humoral: mediated by a secreted substance
usually a protein or glycoprotein
Viruses
Cell
Interferon is a type of
cytokine
Type I
Interferons
Antiviral
State
Upregulate genes/proteins to
produce an anti-viral state
– Some examples:
•
•
•
•
Messengers: cytokines and chemokines
Enzyme Inhibitors: Anti-proteases
Lysins: Lysozyme, antimicrobial peptides
Opsonins: Lectins
No evidence of interferon in invertebrates but
can induce an antiviral state with dsRNA
Rapid cell
suicide to
prevent viral
replication
Returns to
Normal
Robalino et al. 2004
2
Robalino et al. 2005
Robalino et al. 2005
• 1a. Sequence-specific protection
from WSSV ds-RNA; magnitude
of antiviral state varied with
WSSV gene sequence used (IM)
• 1c. dsRNA protection likely
sequence dependent as
antisense RNA to same
gene failed to protect
• 1b. Sequence-independent innate
IR failed to protect (poly(CG))
from high dose WSSV but WSSV
dsRNA protected (per os)
Robalino et al. 2005
Innate Humoral Factors: Lysins
• 1d. dsRNA protection is both
sequence and dose dependent
• Lytic enzymes/cytotoxic molecules
– Lysozyme in some fish and molluscan
species
– Antimicrobial peptides
• Hemocyanin
• 1e. Viral-specific motifs afford
transient innate stimulation and
a delay in onset of mortality but
not full protection as did
dsRNA from the challenge virus
– In crustaceans/gastropods/chitons
– And some bivalves (not oysters,
scallops, mussels)
www.csulb.edu/~gcampus/science/ bio/gastropod/figure5.1.jpg
science.msfc.nasa.gov/.../ dewar_pix/pcg_gallery.htm
Lysozyme
Peptidoglycan
Antimicrobial peptides
• Defense mechanism against bacterial
infections
– Found in mantle, mucus and serum
of Crassostrea spp. and in the
digestive gland and mantle of
Haliotis spp.
– Released during degranulation in
phagocytosis
– Season and health affect levels
• Hydrolysis of bacterial cell walls
– Cleaves the glycosidic bond between
carbon number 1 of N-acetylmuramic
acid and carbon number 4 of N-acetylD-glucosamine
– = carbohydrates that polymerize to
form the cell wall polysaccharide
• Usually + charged
• Destabilize membranes of targets and create
pores  lyse cells
• Pre-pro-peptide: limited lysis to activate
Prepro
peptide
– E.g from protein with other use (recycle)
• Hemocyanin (net negative charge): antifungal
activity in Penaeus vannamei
• Cleavage results in 50x increase in antifugal
activity!
http://www.kingsu.ab.ca/~han
k/Course%20files/Biochemistr
y/lysozyme.htm ; wikipedia
3
Pattern recognition proteins (PRPs)
• LPS and beta glucan binding protein (LGBP)
• Important in innate IR of many invertebrates
• Up-regulated upon exposure to bacteria,
fungi and viruses
• Activates Prophenyloxidase cascade
• Melanin production
• Also suggested role in stimulating
antimicrobial peptide production and release
Innate Cellular Mediators
• Function in nutrient digestion,
metabolite transport, wound &
shell repair
• Main role is in internal defense:
Adaptive
Innate
Cellular
Humoral
Cellular
Innate Cellular Mediators:
Phagocytes
Bacterium
Phagocytosis
1. Pseudopodia capture
bacteria (ROI stimulation)
2. Ingestion to form phagosome
3. Fusion to lysosome
containing enzymes and
toxins
4. Digestion via enzymes such as
lysozyme, acid hydrolases,
lipase, b-glucuronidase,
aminopeptidase
5. Release of digestion products
Humoral
• Cellular: mediated by cells
• Humoral: mediated by a secreted substance
usually a protein or glycoprotein
Hemocyte
– chemotaxis, lectin-mediated
pathogen recognition, phagocytosis,
encapsulation and elimination of
invaders via enzymatic destruction
and/or by the production of
antimicrobial peptides
– How do they signal other cells?
Figure 1-3. Kuby Immunology 4.0 CD ©2000 W.H. Freeman
and Sumunas Multimedia Development Services, Sumanas
Inc.
Cellular and Humoral
Effector Molecules
Bacterium is engulfed
and enters phagosome
Cytokines
Chemokines
lysosome
Lysosome fuses with
phagosome and lysosomal
contents degrades the bacterium
MAP Kinase
(MAPK) signal
transduction
pathway
Releases degraded particles
and glycogen into
hemolymph or commits
suicide by exiting across an
epithelium (diapedesis)
A Good Place To Hide
• Some bacteria or
protists use
phagocytosis to gain
entry into the cell
• Bacteria/protists can
escape the phagosome
or phagolysosome
• Once in the hemocyte,
the pathogen is hidden
from the host immune
system
4
Cellular and Humoral
Effector Molecules
Adaptive
Innate
Cellular
Humoral
Cellular
Humoral
• Cellular: mediated by cells
• Humoral: mediated by a secreted substance
usually a protein or glycoprotein
Possible Cellular Mediators of the
Quasi-adaptive Immune System
• Hemocytes
• ? Do they retain memory of a past
exposure
Quasi-adaptive system of crustaceans
Venegas et al. 2000… Penaeus rod-shaped DNA
virus (PRDV) = WSSV
Cellular and Humoral
Effector Molecules
Adaptive
Innate
Cellular
Humoral
Cellular
Humoral
• Cellular: mediated by cells
• Humoral: mediated by a secreted substance
usually a protein or glycoprotein
• Confirmed that challenged
shrimp were ‘immune’ by rechallenge with virus up to
40d post initial challenge
• To examine for presence of
neutralizing serum factor,
took serum from survivors of
a natural exposure 17d and
40d post challenge and coinjected with virus into naive
shrimp
• Protection at 17d only
– ’quasi-acquired immune
response’
• Neutralizing factor 17d
• Protection vs re-challenge
at least 40d
NS = serum of natural survivors 40d
NES= from NS+rechallenge 17d
5
Adaptive Humoral Mediators:
What are they?
• No antibodies
Summary of Responses
Humoral
• But have/secrete:
– PRPs
– AMPs
– IgSF-domain-containing fibrinogenrelated proteins
(FREPs)
Innate
Opsonins
Lysins
Cytokines/chemokines
• Yet to identify/understand a full spectrum of
mediators and their role in the observed
memory
Cellular
Adaptive
?
Polymorphis
m in immune
gene loci
IgSF domains
(FREPs)
AMPs
(penaeidin)
?
Phagocytes
Immunostimulants
Summary
• Invertebrates have an efficient
immune response
• Beta Glucans (long chain polysaccharide found in
many plant, bacterial and fungal cell walls)
• Structurally resemble bacteria to the immune system
– Mimic the microbial cell capsules and cell walls
• Stimulate hemocytes to synthesize and release
antimicrobial peptides
• Probiotic bacteria in feed
• Once activated  increased metabolic needs
– Considered more primitive than
that of vertebrates
• Many analogs to higher animals
• But lack antibodies
– Quasi-adaptive IR seen in shrimp
• Relies on less specific innate
immune response
– Humoral and cellular facets
• Also seen in higher animals
: www.cat.cc.md.us/.../lecguide/ unit1/bacpath/capc3b.html
6