Immune Evasion Flashcards
What cells are part of the innate immune system?
Neutrophils
Eosinophils
Basophils
Dendritic cells
Macrophages
What do neutrophils do?
Recruited to ares of infection
Detect microbes
Perform effector functions —> kill microbes
Why must Neutrophil responses be balanced?
To prevent infection but also to prevent damage (inflammation) to host
How do neutrophils work?
Microbes enter body and become opsonised with antibodies and complement
Results in production of gradient of C3a and C5a as well as bacterial proteins and peptides
C3a and C5a bind to their receptors on endothelial cells —> endothelial cells express ICAM at their surface
Neutrophils contact endothelial they detect increase in ICAM and adhere to ICAM receptor —> roll along surface of endothelium then transmigrate across endothelial layer
Become primed by gradient of C3a C5a/bacterial proteins and peptides
Migrate towards complementary components and bacterial proteins via chemotaxis
Become activates and perform effector functions —> phagocytosis or degranulation
Neutrophils also recruit other immune cells
What is Staphylococus aureus?
Gram positive bacterium
Commensalism and lives harmlessly in the nose
Opportunistic pathogen and able to cause minor skin infections to severe and life-threatening diseases
What is streptococcus progenies?
Gram positive bacterium
Lives harmlessly in the throat of humans
Opportunistic virus
Able to cause range of disease —> pharyngitis, skin infections, scarlet fever and sepsis
What is antibody opsonisation?
Antibodies bind bacterial antigens allowing:
—> deposition of complement in the classical complement pathway
—> neutrophils and other phagocytes the ability to detect invading microbes
What are strategies bacterial pathogens have to evade being opsonised with antibodies?
Hide antigen
Distrust function
Prevent detection
Degrade antibodies
Modify antigenicity
How are antigens hidden in evasion of antibody opsonisation?
Bacteria express capsule on their surface —> helps bind antigenic structures that can be detected by innate and adaptive immune components
How do surface proteins prevent detection in evasion of antibody sopsoinisation?
Protein bind the antibodies via their Fc region and not their Fab region —> prevents normal opsonisation
How do proteases prevent detection in evasion of antibody opsonisation?
Cleave or modify antibodies —> prevents normal opsonisation
What is the use of antigen variation in evasion of antibody opsonisation?
Switching expression of antigens means antibodies that recognise the first structure are unable to recognise those bacteria now
What is complement opsonisation?
Large number of proteins that react w/ one-another to opsonise pathogens or to directly kill them by membrane attack complex formation
What is the key step of compliment opsonisation?
Deposition of C3b onto surface of the microbe —> can be detected by complement receptors expressed on neutrophils which can phagocytose the microbe
What are the 4 key steps of the complement cascade?
Initiation
Formation of C3 convertase —> amplification of signal
Formation of C5 convertase —> formation of membrane
MAC formation
