insect defences part 2 Flashcards
what does the insect immune response consist of
1) cellular elements
2) humoral elements
= both respond to similar cues such as components of pathogen surface molecules
what is the difference between cellular and humoral defences
cellular - mediated by haemocytes
humoral - mediated by an array of non-cellular mechanisms
what are pathogen-associated molecular patterns aka PAMPS
highly conserved structures which are present in many different micro-organisms which allow recognition by the insect immune responce as non-self
what are pattern-recognition receptors aka PRRs
glycoproteins found on the surface of a variety of defence cells and bind conserved PAMPS
give some example of PAMPS
= lipopolysaccharides - gram negative cell walls
= petidoglycan
= lipoteichoic acids - gram positive cell walls
= mannose bacterial DNA and double stranded virus RNA
= flagellin
what is the difference between a gram negative and a gram positive cell wall
-ive = lipopolysaccharide outermembrane with thin peptidoglycan layer
+ive = no outermembrane and a thick petidoglycan layer
give some examples of insect PRRs
= immulectins = c-type lectins containing 2 carbohydrate recognition domains
- bind to bacterial cell wall components suchs as LPS
= Haemolin = plasma proteins which bind to bacterial surface components
= Toll and toll-like receptors = acts as sensorys of innate immune system and bind many kinds of ligans
what immune responses can be triggered by recognition of PAMPS by different PRRs
- phagocytosis
- nodule formation
- encapsulation
- melanisation
give examples of some haemocytes which are involved in the cellular immune responce
1) prohaemocytes
2) plasmatocytes
3) granular cells/granulocytes
4) coagulocytes
5) spherule cells
6) oenocytoids
7) adipohaemocytes
= classified according to cytology and function
what is a prohaemocyte
thought to be the stem cells from which all haemocytes arise
= round or oval cells
= relativley large nucleus
what is a adipohaemocyte
a fat storage cell
what is a plasmatocyte
invloved in major immunological actions
= exhibit spreading behaviour
= phagocytose small particles
= invloved in encapsulation of microbes
what are granular cells/granulocytes
round cells with small round nucleus and characteristed by the presence of intracellular granules
involved in
- nodulation
- encapsulation
- removal of dead/injrued cells from circulation
- coagulation of haemolmphy
- recognition of foreign bodies
what is phagocytosis
a cellular immune responce where PLs are attracted to certain molecules such as lipopolysaccharides or cell wall componenents
= PLs attempt phagocytosis even if only partly engulfed
what is nodule formation
a cellular immune responce when a large number of bacteria or fungal spores invade
= humoral patterns such as pattern recognition proteins and lectins enhance aggregation by granulocytes
= become surrounded by plasmatocytes to form nodules
= often accompinied by melanisation
what is encapsulation
a cellular immune responce whereby large invaders evoke encapsulation
= like nodule formation but produces larger melanised structures
= granulocytes may adhere to invader and produce factors which recruit other haemocytes
= melanistaion often produced in layer due to activation of PO chains
outline the invlovemnet of the cellular immune responce in wound healing
Clot formed beneath wound
* Involves haemocytes and plasma
* Granulocytes release material which forms a gel, which is then
stabilised
* Phenoloxidases may also have an important role
* Plasmatocytes later migrate to site and become bound together to
form continuous tissue
* Epidermal cells migrate over clot to repair wound
what is the humoral responce
dependant on the primary and secondary responces
1= mediated by activation of cascades of consistuitive proteins in haemolmph
2 = requires transcriptional activation of defence proteins such as induction of anti-microbial peptides
many humoral effectors are derived from the fat body, give some examples
- Antimicrobial peptides (AMPs)
- Opsonins (components of melanisation clotting system)
- Catalase (limits reactive oxygen species produced)
- Transferrin (reduces free iron for microbial proliferation)
- Lysosyme (hydrolyses link in bacterial cell walls)
outline melanisation as part of the humoral immune responce
*Phenoloxidase (PO) is highly reactive and the enzyme responsible for
melanin synthesis
* Toxic quinone intermediates and reactive oxygen and nitrogen
species are produced during melanin formation
* Mechanical injuries or presence of pathogens result in melanin
deposition around damaged tissue, isolating and preventing
development of pathogen
*POs also important for pigmentation and sclerotisation of many tissues
* PO exists in inactive form – proPO and stored in circulating
haemocytes
* Released in response to wounding or microbial products
* Activated by limited proteolysis through action of specific serine
protease
* PO activation and melanisation also play key role in coagulation of
haemolymph and clot formatio
what are anti-microbial peptides (AMPs)
cationic peptides which are less than 100 amnio acid residues
= have an amphipathic structure (charged and hydrophobic areas)
= generate pores in the membrane or penetrate, bind and disrupt intracellular targets
= synthesised in the fat boyd or in gut cells in responce to infection and released into haemolpmph
how is anti-microbial peptide transcription actovated
Via IMD (immune deficiency) signalling
pathways in response to Gram- bacteria
binding to receptors = peptidoglycan
recognition proteins (PGRPs) (a type of PRR)
on surface of insect cells
* Via Toll signalling pathway activated by
Gram+ bacteria and fungi
outlie AMP specificity
- Defensins (4 kD) Lyse bacterial cells by formation of membrane
channels – occur across animal kingdom - Cecropins (3-4 kD) Act like detergents, killing many, but not all,
bacteria - Gram +ve and –ve bacteria – creates membrane channels
– found in various insects - Attacins (22-28 kD) Much narrower range - Gram -ve bacteria.
Prevent bacterial cell division by inhibiting biosynthesis of outer
membrane proteins – in various insects - Diptericin (8.6 kD) Active only against limited range of Gram‐ve
bacteria. Seems to function by disrupting cytoplasmic membrane of
growing bacteria
