ANTIBODY FUNCTION

what are the biological roles of antibodies

complement activation

antibody dependent cell mediated cytotoxicity

passive immunity

neutralisation

opsonisation

agglutination

define complement

series of plasma proteins that are part of the innate immune system

what are the functions of the complement system

induce cell lysis

promote inflammation

promote phagocytosis

remove immune complexes

with the example of a microbe explain C3b opsonisation and phagocytosis

1. chemotaxis

2. recognition and attachment → complement receptors on phagocytes recognise the C3b coated target molecule

3. engulfment

4. phagosome maturation and phagolysosome formation

5. destruction and digestion

6. exocytosis

what are the 3 complement activation pathways

classical → antibody mediated

alternative

lectin

explain the antibody activation of complement

It is overall cell lysis via a classical pathway

a cascade of reactions leads to formation of MAC

this is initiated by the binding of antibodies-antigen, IgM and IgG

what is MAC

the membrane attack complex

many many holes in the target cell

explain antibody dependent cell mediated cytotoxicity

NK cells detect antibody coated cells via exposed Fc receptors

they release toxic granules to kill the target cells

only IgG is involved

describe briefly the missing self hypothesis

when NK cells target a cell by recognising absence of surface MHC 1 molecules

explain the relationship between IgE and parasites

IgE will bind to the surface of parasites

Then Fc receptors on eosinophils and mast cells bind to the IgE Fc portion

eosinophils degranulate and release peroxidase, lysosomal enzyme etc

what can an allergic reaction be denoted as

an inappropriate immune response

what is involved in the primary immune response to an allergen

IgE bound basophils/mast cells

what is involved in the secondary immune response to an allergen

degranulation/release of histamine

what is maternal Ig transfer

when immunoglobulins from the mother pass to the foetus via the placenta

what immunoglobulins are transferred during gestation

IgG_1,3,4

when do foetal IgG levels rise in gestation

3-4 months

when does foetus make own IgG

3-4/4-8 months post partum

when does foetus make own IgM

1-3 months prior to birth

what is a downside of maternal transfer

haemolytic disease of newborn may occur

this is when the antibodies from mum react with the foetal red blood cells

explain what happens in the first exposure of Mums immune system for haemolytic disease

Mum has Rh (-) rbc (D)

the first baby is Rh(+) (D)

the foetal rbc leak into maternal blood in birth

mum B cells primed to make anti-D antibodies

explain what happens in second exposure of Mum’s immune system in haemolytic disease

Haemolytic disease will occur if mum still has or makes anti-Rh D IgG antibodies

maternal antibodies cross the embryonic chorion and bind to the D antigen on the baby rbc

this can threaten infant life

how do we get antivenom

by milking venom, and injecting another animal with it

the injected animal will produce antibodies against the venom which we then harvest

what is the function of neutralisation

prevents the binding and entry of toxins to a target cell

explain how neutralisation works

antibodies bind to the toxin or virus

this means toxins and viruses cannot bind to cells

the antibody antigen complex will be removed by phagocytosis or complement

what substances can be neutralised

toxins and viruses

which cells are involved in phagocytosis without antibodies

neutrophils, monocytes, dendritic cells and eosinophils

explain the steps in antibody free phagocytosis

1. microbe adheres to phagocyte

2. phagocyte forms pseudopods and engulfs the particle

3. phagolysosome forms

4. microbe is killed and digested by enzymes, leaving a residual body

5. indigestible and residual material is removed by exocytosis

define opsonisation

the process of antibodies binding to an epitope on an antigen molecule on the target particle, effectively coating the particle and marking it for phagocytosis

what is an opsonin

a target particle coated in antibodies

which antibody is involved in opsonisation

IgG only

how does agglutination enhance phagocytosis

by reducing the # of infectious units to deal with

which antibodies are involved in agglutination

IgM,A,G

where is IgD present

on mature B cells with IgM

what is the function of IgD

to act as specific B cell receptor for B cell activation

what can secrete IgD

small amounts can be secreted by mature memory B cells which have been activated upon secondary exposure

what part of the body is IgD seemingly important in

the upper respiratory tract