L27: immunology 3

how do antibody Fab arms protect against infection + state which immunoglobulins utilise each method

neutralise - IgG + IgA

immobilise motile microbes - IgM

prevent binding to + infection of host cells

form complexes

how do antibody Fc regions protect against infection + state which immunoglobulins utilise each method

activate complement - IgG + IgM

bind Fc receptors

which immunoglobulins bind to phagocyte Fc receptors

IgG + IgA

which immunoglobulins bind to NK cell Fc receptors

IgG

which immunoglobulins bind to mast cell Fc receptors

IgE

what is the role of compliment

defence against bacteria + some role in defence against viruses

what is the compliment classical pathway

activation specifically by antigen/antibody complexes

name the 3 pathways of compliment activation

classical, MB-lectin, + alternative

how is the classical compliment pathway activated

two antibodies bind to one antigen → C1 interacts with 2 Fc regions to be activated → activation of C1, C4, + C2 leads to generation of a C3 convertase → C3 cleaved into C3a + C3b → C3b joins C3 convertase to make C5 convertase

what are the 3 major biological activities of compliment

activation of WBCs - C5a + C3a (less potently)

opsonization (inc. binding + phagocytosis) - C3b

cell lysis - membrane attack complex (C5-9)

how does C9 attack the membrane of a bacteria

hollow cylinder shape that forms pores in membrane

which types of bacteria are not susceptible to the membrane attack complex

gram +ve

what is an opsonin

EC proteins that induce phagocytosis when bound to a cell

which classes of antibodies can act as opsonins

IgG + IgA

how do antibodies induce phagocytosis

antibodies coat bacterium + Fc receptors of phagocyte bind to antibodies → pseudopods extend + fuse to form a phagosome → lysosomes fuse with the phagosome to form a phagolysosome

how is bacteria killed in a phagolysosome

enzymes (lysozymes)

competitors (lactoferrin)

reactive oxygen species (H₂O₂)

what occurs when antibodies bind to Fc receptors on NK cells

IgG mediates antibody dependent cell-mediated cytotoxicity (ADCC)

secretions (e.g. perforin) cause target cell to undergo apoptosis

what occurs when antibodies bind to Fc receptors on mast cells

IgE mediates allergy or defence against large parasites

IgE binds to specific Fc receptors on sensitised mast cells → allergen bound to IgE activates mast cell + causes degranulation → releases inflammatory mediators (e.g. histamines) causing local inflammation

what is antisera

serum with antibodies

what is the polyclonal b cell response

the activation of multiple different b cell clones specific to different epitopes on the same antigen

define epitope

‘shape’ an antibody binds to

what are the issues with the polyclonal b cell response

may lack fine specificity + difficult to standardise

also differences between animals or even different bleeds from the same animal

what are monoclonal antibodies

identical antibodies derived from a single B lymphocyte

how are monoclonal antibodies produced

B cells taken from an animal immunised with a specific antigen + fused with a tumour cell line → results in hybrid cells that make a specific antibody + divides indefinitely

state the 4 functions of antibodies in research, diagnostics, + therapy

1. ID + label molecules in complex mixtures

2. ID pathogens

3. characterise cell surface proteins + ID cell types

4. humanised antibodies used in therapy