Insect Immunity Flashcards
With insect immunity, the innate immune system is split into two parts. What are these parts and what function do they have?
The innate immune system of insects is split into the systemic/humoral part and the local part. With the systemic/humoral part, the fat body secretes antimicrobial peptides (AMPs) upon infection into the haemolymph that circulates through the whole insect, and reactive oxygen species (ROS) are produced. The local system consists of a cellular response with haemocytes.
What electrical charge do antimicrobial peptides (AMPs) secreted by insects have?
Most AMPs are cationic (positively charged). This positive charge allows the AMPs to attack the negatively charged parts of the bacterial membrane; AMPs disorganise the anionic bacterial cell membrane.
Do insects produce one kind of antimicrobial peptides (AMPs) or more?
Insects secrete specific AMPs for specific pathogens.
Which protein plays an important part in the production of reactive oxygen species in insect innate immunity?
Transmembrane protein dDuox.
Which types of haemocytes are present in Drosophila melanogaster, and which are not present in Drosophila melanogaster?
Crystal cells, plasmatocytes, and lamellocytes are present in Drosophila melanogaster. Spherulocytes, prohemocytes, and granulocytes are not present in Drosophila melanogaster.
What is the function of plasmatocytes in insect immunity, and which proteins play an important role in this function?
Plasmatocytes can conduct phagocytosis. In this phagocytosis, scavenger receptors, eater proteins, and DSCAM play a very important role.
Why does DSCAM have a very peculiar organisation in the genome of insects?
DSCAM has various alternative exons, of which only 1 comes to fruition at a time, resulting in the possibility to make a lot of different receptors. It has been questioned if DSCAM can provide insects with an adaptive immune response, similar to the human immunoglobulin genes.
What is the function of lamellocytes in insect immunity?
Lamellocytes can conduct encapsulation. Lamellocytes differentiate and migrate to the infection.
What is the function of crystal cells in insect immunity, and which protein plays an important role in this function?
Crystal cells can conduct melanisation, where prophenoloxidases play a very important part.
Parasitic wasps can lay eggs in the larvae of flies. How does the insect immune system combat this?
Lamellocytes differentiate and migrate to the infection and encapsulate the eggs. Then, the eggs are melanised by crystal cells. Larval haemocytes stay in principal in the lymph gland but can leave in case of an infection.
Which two main signalling pathways are present in the insect innate immune system, and how are they activated?
The Toll pathway and the IMD pathway. The Toll pathway recognises the lysine in the peptidoglycan in the cell wall of Gram-positive bacteria, but is also activated by fungi and yeast. The IMD pathway recognises the mesodiaminopimelic acid in the peptidoglycan of Gram-negative bacteria. However, they don’t exclusively activate one pathway or the other; bacilli, Gram-positive bacteria, synthesise diaminopimelic acid peptidoglycan, which activates the IMD pathway, but their microbial patterns activate the Toll pathway.
How does the IMD pathway signalling cascade work?
Upon activation, PGRP-LC recruits IMD, DFADD, and Dredd. Dredd activates dTAK1 and its dTAB2, which activate Relish. Dredd is also a caspase that cleaves activated Relish from its inhibitory IkB domain. The NFkB domain of Relish can enter the nucleus as a transcription factor, which results in the synthesis of AMPs, prevention of self-tissue damage, haemocyte proliferation/differentiation, and induction of phagocytosis.
How does the Toll pathway signalling cascade work?
After recognition, a proteolytic cascade leads to the cleavage of Spätzle, that can bind to and activate the Toll-receptor. The intracellular pathway then leads to the degradation of Cactus to free the Dorsal/Dif for nuclear translocation. These NFkBs can enter the nucleus as transcription factors, resulting in the synthesis of AMPs, prevention of self-tissue damage, haemocyte proliferation/differentiation, and induction of phagocytosis.
How does insect Toll differ from vertebrate Toll?
In comparison to vertebrates, Toll is not a pattern recognition protein, but it is activated by a ligand. The pattern recognition proteins in the Toll or IMD pathway do not recognise lipopolysaccharides, like they do in vertebrates, but peptidoglycans.
What are the seven distinct antimicrobial peptides (AMPs) that Drosophila secretes during an infection?
Drosomycins and metchnikowin against fungi. Defensins against Gram-positive bacteria. Attacins, cecropins, drosocins, and diptericins against Gram-negative bacteria.
