Insect Defences 2

Question 1

What does insect immune response consist of?

Answer 1

cellular and humoral elements

Question 2

Cellular + humoral defences respond to…

Answer 2

…similar cues, e.g. components of pathogen surface molecules (sugars, lipopolysaccharides, proteins)

Question 3

cellular defences mediated by…

Answer 3

… haemocytes

Question 4

humoral defences mediated by…

Answer 4

…array of non-cellular mechanisms

Question 5

name of the structures that the immune system is designed to recognise?

Answer 5

pathogen-associated molecular patterns (PAMPs)

Question 6

insects and mammals have evolved…

Answer 6

…pattern-recognition receptors (PRRs) that bind conserved PAMPs

Question 7

what are PRRs?

Answer 7

glycoproteins found at surface of variety of defence cells

Question 8

gram -ve cell wall

Answer 8

consists of a single layer of peptidoglycan and has a layer of outer-membrane consisting of lipopolysaccharide, membrane proteins and porins

Question 9

gram +ve cell wall

Answer 9

Gram-positive bacteria are surrounded by many layers of peptidoglycan (PG), which form a protective shell that is 30–100 nm thick (Silhavy et al. 2010).

Question 10

PRRs recognise + bind…

Answer 10

…PAMPs - microbial molecular components NOT part of eukaryotes

Question 11

What immune responses can be triggered by the recognition of PAMPs by different PRRs (esp toll and toll-like receptors)

Answer 11

phagocytosis

nodule formation

encapsulation

melanisation

Question 12

cellular immune response

Answer 12

• haemocytes play crucial role in wound healing + protection against infection throughout life of insect
• secretion of compounds, e.g. phenoloxidase (contributes to humoral immunity)
• direct involvement via cellular immunity
• remove small particles by phagocytosis - microbes delivered to lysosomes + destroyed

Question 13

cellular immune responses include…

Answer 13

phagocytosis

encapsulation

nodule formation

wound healing

Question 14

Humoral immune response
Melanisation

Answer 14

• Phenoloxidase (PO) = highly reactive + enzyme responsible for melanin synthesis
• toxic quinone intermediates + reactive oxygen + nitrogen spp produced during melanin formation
• mechanical injuries/presence of pathogens = melanin deposition around damaged tissue, isolating + preventing development of pathogen
• POs also important for pigmentation + sclerotisation of many tissues
• PO inactive form = proPO + stored in circulating haemocytes
• released in response to wounding or microbial products
• activated by limited proteolysis through action of specific serine protease
• PO activation + melanisation also play key role in coagulation of haemolymph = clot formation

Question 15

Toxic intermediates + reactive oxygen/nitrogen species

Answer 15

• activation of proPO system = rapidly triggered upon pathogen invasion or injury to cuticle
• during proPO activation, reactive oxygen and nitrogen intermediates (e.g. peroxides) made
• cause oxidative damage to pathogens directly or indirectly
• melanin + intermediates in its synthesis = toxic

Question 16

Anti-microbial peptides (AMPs)

Answer 16

Cationic peptides < 100 aa residues (15-50)

Amphipathic structure = charged + hydrophobic areas

generate pore in membrane, or penetrate, bind + disrupt intracellular target

synthesised in fat body or in gut cells in response to infection + released into haemolymph

Question 17

Anti-microbial peptides

Answer 17

transcription acitvated:
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 18

AMP specificity

Answer 18

• Defensins (4 kD) Lyse bacterial cells by formation of membrane channels - occur across animal kingdom
• Cecropins (3-4 kD) act like detergents, killing many, not all, bacteria - Gram +ve and -ve bacteria - creates membrane changes - various insects
• Attacins (22-28 kD) narrower range - Gram -ve bacteria. prevent bacterial cell division by inhibiting biosynthesis of outer membrane proteins - 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