insect defences part 2

Question 1

what does the insect immune response consist of

Answer 1

1) cellular elements
2) humoral elements

= both respond to similar cues such as components of pathogen surface molecules

Question 2

what is the difference between cellular and humoral defences

Answer 2

cellular - mediated by haemocytes

humoral - mediated by an array of non-cellular mechanisms

Question 3

what are pathogen-associated molecular patterns aka PAMPS

Answer 3

highly conserved structures which are present in many different micro-organisms which allow recognition by the insect immune responce as non-self

Question 4

what are pattern-recognition receptors aka PRRs

Answer 4

glycoproteins found on the surface of a variety of defence cells and bind conserved PAMPS

Question 5

give some example of PAMPS

Answer 5

= lipopolysaccharides - gram negative cell walls
= petidoglycan
= lipoteichoic acids - gram positive cell walls
= mannose bacterial DNA and double stranded virus RNA
= flagellin

Question 6

what is the difference between a gram negative and a gram positive cell wall

Answer 6

-ive = lipopolysaccharide outermembrane with thin peptidoglycan layer

+ive = no outermembrane and a thick petidoglycan layer

Question 7

give some examples of insect PRRs

Answer 7

= 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

Question 8

what immune responses can be triggered by recognition of PAMPS by different PRRs

Answer 8

• phagocytosis
• nodule formation
• encapsulation
• melanisation

Question 9

give examples of some haemocytes which are involved in the cellular immune responce

Answer 9

1) prohaemocytes
2) plasmatocytes
3) granular cells/granulocytes
4) coagulocytes
5) spherule cells
6) oenocytoids
7) adipohaemocytes

= classified according to cytology and function

Question 10

what is a prohaemocyte

Answer 10

thought to be the stem cells from which all haemocytes arise
= round or oval cells
= relativley large nucleus

Question 11

what is a adipohaemocyte

Answer 11

a fat storage cell

Question 12

what is a plasmatocyte

Answer 12

invloved in major immunological actions
= exhibit spreading behaviour
= phagocytose small particles
= invloved in encapsulation of microbes

Question 13

what are granular cells/granulocytes

Answer 13

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

Question 14

what is phagocytosis

Answer 14

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

Question 15

what is nodule formation

Answer 15

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

Question 16

what is encapsulation

Answer 16

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

Question 17

outline the invlovemnet of the cellular immune responce in wound healing

Answer 17

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

Question 18

what is the humoral responce

Answer 18

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

Question 19

many humoral effectors are derived from the fat body, give some examples

Answer 19

• 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)

Question 20

outline melanisation as part of the humoral immune responce

Answer 20

*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

Question 21

what are anti-microbial peptides (AMPs)

Answer 21

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

Question 22

how is anti-microbial peptide transcription actovated

Answer 22

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

Question 23

outlie AMP specificity

Answer 23

• 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