Abstract Multicellular organisms constantly encounter potentially harmful microorganisms. Although insects lack an adaptive immune system, they do have powerful means of fighting infections. Cellular responses involve phagocytosis of bacteria and encapsulation of parasites. In addition, insects can mount a humoral response against pathogens. This is characterized by the secretion of antimicrobial peptides into the hemolymph. Recognition of foreign pathogens involves specific receptors for sensing infection. These include peptidoglycan recognition proteins (PGRPs) and β‐glucan recognition proteins (βGRPs). Engagement of these receptors starts signaling pathways that activate the genes that encode antimicrobial peptides. These pathways include the Toll, the Imd, and the JAK‐STAT.

3. Mogili Ramaiah
IARI, Ph.D Scholar
Division of Entomology
New Delhi-110012
Welcome
Term-Paper Presentation
SIGNALING PATHWAYS FOR INSECT
IMMUNE SYSTEM

4. Contents
 Introduction
 History
 Insect Immune System
 Antimicrobial Peptides
 Signaling pathways activating genes
 Summary
 Conclusion
 References

5. Introduction
 Animals
 Plants

6. Introduction
 Greek word “immunis” meaning exempt.
Resistance to infection
 Immunity : The ability of an organism to resist to a
particular infection
 Insects have evolved cellular and molecular defense
mechanisms against infection, these defense mechanisms
called “ IMMUNITY”.

7. History of Immunology
Louis Maupertuis
(1698-1759)
Experiment :

8. Paul Ehrlich
(1854-1915)
Proposed : Side chain theory
(antigen-antibody reaction)
Founder of cellular immunology
Noble prize – 1908 (Physiology
and medicine)
Father of natural immunity

9. Élie Metchnikoff
(1845-1916 )
Discovery of phagocytes( macrophages)
Major defense mechanism in innate immunity
Noble prize in physiology and medicine (1908)
Father of innate immunity

10. Edward Jenner
(1749-1823)
Pioneer of small pox vaccine
He used it in 1796 in the long title
of his Inquiry into the Variolae
vaccinae known as the Cow Pox
Father of immunology
Rudolf W. Glaser first reported the existence of immunity in the
grasshopper (Glaser, 1918)

11. Innate immune
response
Adaptive immune
response
Pathogens

12.  In born
 Present in the body at
all times
 Responds immediately
upon infection
 Responds in the same
way regardless of
infection
 Unable to keep
immunological
memory
Adaptive immunity
 Acquired
 Occurs after the
individual is exposed
to the pathogen
 Slow response
 Responds in a
pathogen and antigen
specific manner
 Keeps immunological
memory for longer
period

13. Insect immune system
Cellular immune
response
Humoral immune
response
Phagocytosis
Nodulation
Encapsulation
TOLL , IMD, JAK/STAT, JNK
– Production of AMPs

14.  PRPs – Pattern Recognition proteins
1. PAMPs- Pathogen Associated Molecular Pattern
2. DAMPs- Damage Associated Molecular Pattern
PRRs- Pattern-Recognition Receptors
Membrane-bound PRRs
1.Receptor kinases
2.Toll-like receptors
3. mannose receptor
Cytoplasmic PRRs
1.NOD-like receptors - Nucleiotide oligomerization Domain
(Bacterial)
2. RIG-like receptors – Retinoic acid Inducible gene (Viral)

16. Antimicrobial Peptides
AMPs are small, 12-50 amino acids, cationic peptides,
which bind anionic bacterial or fungal membranes
leading to disruption and cell death
(Zasloff, 2002; Yount and Yeaman, 2006)

17.  In spite of great differences in size, amino acid composition and
structure, most of the antimicrobial peptides from insects can be
grouped into one of three categories. The largest category in number
contains
 1.Peptides with intramolecular disulfide bonds forming hairpin-like
beta-sheets or alpha-helical-beta-sheet mixed structures.
 2. Peptides forming amphipathic alpha-helices.
 3.Peptides with an over representation in proline and/or glycine
residues.
 Two types of mode of action:
 1. through peptide-lipid interaction or
 2. through receptor-mediated recognition processes.

18. Antimicrobial peptides:
Antifungal
Antiparasitic
Antibacterial
Gram positive
Gram negative
Antiviral ? In insect
What do they do?

19.  Over 150 antimicrobial peptides (AMPs) have been isolated and
characterized in insects.
 Insect AMPs can adopt certain structures or contain unique
sequences and thus can be classified into four groups:
1. α-helical peptides (e.g., cecropin and moricin),
2. Cysteine-rich peptides (e.g., insect defensin and drosomycin),
3. Proline-rich peptides (e.g., apidaecin, drosocin and lebocin), and
4.Glycine-rich proteins (e.g., attacin and gloverin)
(Bulet and Stocklin, 2005; Otvos, 2000).

20. Cecropins were firstly isolated in H. cecropia after injection with
bacteria (Hultmark et al., 1980; Steiner et al., 1981). These peptides
are produced in response to septic injury by either Gram positive or
Gram negative bacteria and affect on cellular proliferation by
inhibiting the synthesis of proteins of the cell membrane.
Defensins and drosomycin are cysteine-rich peptides. Defensins,
destroy mostly gram-positive bacteria by forming channels in the
plasma membrane which leads to cell lysis, while drosomycin has an
antifungal activity.
Diptericin is an antibacterial peptide that has been found only in
diptera species and is induced upon Gram negative bacteria
infection in a way similar to attacins (Nappi and Ottaviani, 2000).

21. General activity spectra of AMP families
AMP family Acts against
Attacin Anti bacterial (Gram -)
Cecropin Anti bacterial (Gram -)
Defensin Anti bacterial (Gram +)
Diptericin Anti bacterial (Gram -)
Drosomycin Antifungal
Drosocin Antibacterial (Gram -)
Metchnikowin Antifungal

22. Insect antimicrobial peptides

23. AMPs

24. Signaling Pathways:
 The Toll pathway has a dual function, being central in
developmental processes
 Imd functions exclusively in immunity. Both pathways form part
of the humoral immune response that is triggered by the
recognition of microbes and results, via multiphase signal
transduction, in the secretion of antimicrobial peptides and other
microbe-targeting substances.
 Multipurpose pathways JNK and JAK/STAT also contribute to
immunity
 RNA interference is essential to viral defense

25. The Toll pathway
 Peptidoglycan recognition proteins
(PGRP)
 Spaetzle - processing enzyme (SPE)
and other proteases
 Serine protease Persephone (Psh)
 Myeloid differentiation primary
response 88 (dMyD88), Tube, and
Pelle,
 Cactusis normally bound to the
Nuclear Factor kappa B (NF-κB)
transcription factors Dorsal-related
Immunity Factor (DIF) and Dorsal
kinase
(Stokes et al., 2015

26. The IMD pathway
 Direct binding between PGRP-LC and
meso-diaminopimelic acid (DAP)-type
PG of Gram-negative bacteria.
 intracellular adaptor protein Immune
deficiency (Imd)
 Drosophila Fas - associated death
domain (dFADD) and the Death related
ced-3/Nedd2-like caspase( DREDD)
 Immune Response Deficient 5 (IRD5)
and Kenny (Key).
(Stokes et al., 2015

27. JAK/STAT Pathway
 It involves binding of the cytokine
ligand UPD to the transmembrane
receptor DOME, thereby inducing
phosphorylation of DOME by the
receptor-associated JAK tyrosine
kinase HOP.
 This phosphorylation creates a
docking site for inactive
cytoplasmic STAT proteins that in
turn are phosphorylated,
dimerised, and translocated into
the nucleus, where they activate
the transcription of numerous
target genes.
(Stokes et al., 2015

28. GNBS
In Brief

29. RNAi gene silencing technology
B2 – FHV(flock house virus)
A1 – CrPV (Cricket Paralysis Virus)

31. Summary
S.N Component TOLL
Pathway
IMD
Pathway
JAK/STAT
Pathway
1 Signaling molecule
2 Receptor
3 Modulator
4. Cellular activators or
second messengers
5 Transcription factor
6 Cellular effects
7. Example - Pathogens

32. Conclusion
 Molecular understanding of their mechanism of action is
still lacking.

33. “If your positivity immune system is low,
Any exposure to a person afflicted negativity can poison your life”

35. Questions
Why we need to study Immune system of insects?
 Innate Immunity Vs Adaptive Immunity
Important terms AMPs, PRPs, PRRs, JAK/STAT, JNK,
PAMPs, DAMPs etc
Signaling pathways for activating genes
