B-cells & Antibodies Flashcards
Primary immune response
Occurs upon first exposure to antigen
IgM is initially detected in the serum and levels then rapidly decrease as the switched antibody response takes over
The switched antibody response occurs after 4-7 days, during which, illness will be apparent
Secondary immune response
Occurs upon subsequent exposure to the same antigen
The IgM response occurs as usual, but the switched antibody response takes over much more rapidly and reaches a higher titre
During this response, illness is not apparent
Functions of antibody
- Neutralisation of toxins
- Opsonisation of pathogens
- Activation of complement
- Agglutination
- Mediation of antibody-dependent cell-mediated cytotoxicity
Class switching
The process by which the antibody class changes
Determined by the cytokine environment and mediated by T-helper cells
Changes occur in the Fc region only; so antibody specificity is unchanged
T-dependent B-cell activation
T-dependent antigens require help from T-cells to complete activation
The antigen binds to the BCR and this complex is recognised and internalised and degraded
The peptide antigen is then presented on MHC class II molecules to recruit T-helper cells
Type I T-independent B-cell activation
Type I T-independent antigens generate a polyclonal response without needing reference to a specific receptor
Examples include TLRs
Type II T-independent B-cell activation
Type II T-independent antigens are large with repeating structures
These antigens bind multiple receptors on the same cell and receptor cross-linking leads to activation of the cell
Memory B-cells are not formed from this type of activation
Lymphocyte diversity
The genes encoding the BCR are rearranged during development
This is carried out by recombination activating genes (RAG)
