- B cells
- Humoral immunity (against extracellular pathogens).
- Recognize antigen—undergo somatic hypermutation to optimize antigen specificity.
- Produce antibody—differentiate into plasma cells to secrete specific immunoglobulins.
- Maintain immunologic memory—memory B cells persist and accelerate future response to antigen.
- T cells
- Cell-mediated immunity (against intracellular pathogens).
- CD4+/helper T cells help B cells make antibodies and produce cytokines to recruit phagocytes and activate other leukocytes – T helper cells call for help!
- CD8+/cytotoxic T cells directly kill virus-infected cells.
- Delayed cell-mediated hypersensitivity (type IV).
- Acute and chronic cellular organ rejection.
- Rule of 8: MHC II × CD4 = 8; MHC I × CD8 = 8.