Flashcards in Immunology Deck (33):
Do lymphatic vessels have valves?
They prevent reverse flow.
What is the main role of the lymphoid system?
React decisively and precisely against foreign invasion.
What are some forms of innate immunity?
What are some forms of adaptive immunity?
T and B cells.
Acquired antigen specific immunity and humoral and cell mediated immunity.
Through what mechanisms is innate immunity enforced?
Body temperature - higher temperatures decrease viability of invading pathogens.
Skin and mucosal membranes - mucous, motility of gut and cilia and normal bacteria flora.
Antimicrobial substances in blood and body fluids - protective serum proteins, lysozyme, complement, interferon, commensals.
Phagocytic cells ( neutrophils, macrophages, NKC).
What are some examples of antimicrobial peptides in vertebrates?
Peptides with hydrophobic motifs that disrupt bacterial cell walls.
Cathelicidins - epithelial cells, macrophages, neutrophils.
Cecropins - insects
Crotamine - rattlesnake venom
What are commensals and what is their role?
Role in innate immunity.
Bacteria that live on host but neither has much effect on each other - competition for invading bad bacteria.
What are some actions that the body carriers out that are associated with innate immunity?
What is complement?
Series of plasma proteins (made in liver) that get activated in a triggered enzyme cascade.
Major defence system of the body.
What are the 3 ways of activating the complement cascade?
What occurs during the classical pathway of the complement cascade?
1) C1 binds Ab:Ag causing conformational change.
2) C1r is activated, C1s is activated.
3) C4 cleaved into a and b.
4) C4b cleaves C2 into a and b.
5) C4b binds C2a
6) C4b2a cleaves C3 into a and b.
How is the classical pathway regulated?
C1 inhibitor (binds C1r and C1s).
Block of C4b2a (C3 convertase).
Control proteins block complement binding to cell surface.
What occurs during the alternative pathway?
Spontaneous - doesn't require antibody (IgA).
C3b binds to hydroxyl and amine groups on micro-organisms cell surface.
Part of innate immunity.
How is the alternative pathway regulated?
Positive feedback inhibition
What occurs during the lectin pathway?
Mannan binding lectin (MBL) binds to mannose groups.
Activates 2 proenzyme serine proteases (homologous to C1r and C1s).
What is MBL?
Mannin binding lectin (collagen like lectin) that binds to yeasts, bacteria, viruses and parasites to initiate the complement cascade.
What are lectins?
Proteins that bind sugar.
What are collectins?
Collectins can aggregate pathogens, neutralise viruses, attract and activate phagocytosis.
Key role in host defence.
What is the end result of the complement cascade?
Production of a membrane attack complex that binds to pathogens membrane.
Which 2 pathways generate C3 convertase? What does it do?
Converts C3 to C3b - C3b then activates the terminal sequence leading to production of the membrane attack complex.
Occurs in classical pathway in response to antigen/antibody complexes.
Occurs in alternative pathway (innate) in response to micro-organisms.
What are the 3 proteins that affect C3b?
C1 inhibitor - inactivates C1.
Protein H - inhibits binding of factor B to membrane bound C3b.
Factor I - cleaves membrane bound C3b into c and d (inactive). Occurs mostly on RBC's.
What are the 3 effector mechanisms? What does complement enhance?
What is opsonisation?
Coating of microorganism with complement proteins, C3b.
Leads to binding of phagocytic cells via complements receptors and enhanced phagocytosis.
Requires a complement receptor.
What is chemotaxis?
Attraction of polymorphs to sites of inflammation via complement receptors.
How does lysis occur?
Via MAC formation of lytic pore.
List some complement receptors.
How can pathogenic bacteria evade complement?
Bacterial capsule that resists opsonisation
How can viruses evade complement?
CR2 is Epstein Barr Virus entry receptor.
CR3 is West Nile Virus entry receptor.
How can yeast evade complement?
Express CR2 and 3 molecules.
Regulate C cascade.
How can Trypanosomes evade complement?
Molecules inhibit complement activation.
What diseases can occur if your complement system is overactive?
Immune complexes deposited on surfaces - bacterial endocarditis, glomerulonephritis.
Anaphylaxis - bacterial sepsis, cardiovascular collapse.
What can occur if their are deficiencies in the complement components?
Lack of C3 - overwhelming bacterial infections
Lack of C8 - Neisserial infections