12 - B Cell Mediated Immunity (in depth first half) Flashcards
What two forms to antibodies exist in
Membrane bound and secreted antibodies
Membrane bound antibodies
On the surface of B lymphocytes function as antigen receptor
Secreted antibodies
Neutralise toxins, prevent the entry and spread of pathogens, and eliminate microbes.
Antigen binding site
The V region of one heavy chain (VH) and the adjoining V region of one light chain (VL) form an antigen-binding site
Antigen binding surface
Three hypervariable regions of a VL domain and the three hypervariable regions of a VH domain are brought together to create an antigen-binding surface
Alternative name for the three hypervariable regions
Complementarity determining regions (CDRs): CDR1, CD2, and CDR3
Which of the three CDRs is the most variable
CDR3, which has the most extensive contact with the antigen
Affinity
- The strength of the binding between a single combining site of an antibody and an epitope of an antigen
- Represented by a dissociation
constant (Kd)
Dissociation constant
- Smaller Kd indicates a stronger or higher affinity interaction because a lower concentration of antigen and of antibody is required for complex formation
- USually varies from 10^-7M to 10^-11M
Avidity
Overall strength of attachment that takes into account binding of all the sites to available epitope
Where are class-switched, high affinity antibody secreting plasma cells produced
Germinal centres
Functions of antibodies
- Neutralisation of microbes and toxins
- Opsonisation and phagocytosis of microbes
- ADCC
- Phagocytosis of microbes opsonised with complement fragments (e.g. C3b)
- Inflammation
- Lysis of microbes
Recognition of antigen by antibody
Involves non covalent, reversible binding
Opsonised antigens
Enter lymph nodes from afferent lymphatics and bind to complement receptors on the surface of macrophages present in subcapsular sinus
Subcapsular macrophages
Capture and preserve opsonised antigens to allow B cells to encounter them
