Cell-mediated immunity involves T cells that recognize and eliminate intracellular pathogens. MHC class I presents endogenous antigens to activate CD8+ cytotoxic T cells to kill virally infected cells, while MHC class II presents exogenous antigens to CD4+ helper T cells to upregulate immune functions against bacteria. Humoral immunity involves B cells maturing into plasma cells upon antigen recognition, secreting antibodies, and leaving memory B cells to facilitate a faster response upon reexposure.

1. Prithvi
M.Sc. Bioinformatics - II
Cell Mediated & Humoral
Immunity

2. Cell – Mediated Immunity
 Unlike humoral immunity, which is designed to react against
extracellular antigens, cell-mediated immunity is much better at
recognizing and eliminating microbes that are within cells.
Major key players :
 MHC I & MHC II
 CD4 & CD8 proteins
 Helper & Cytotoxic T cells
 Antigen Presenting Cells ( APC )
 T – Cell Receptors ( TCR )

4. Type of T cell activated
 MHC class I activates CD8 +T cytotoxic cells
 Present endogenous (eg viral) antigens
 Target cell is killed by CD8 cell
 Any cell can become virally infected
 Therefore: MHC class I is on all nucleated cells

6. Type of T cell activated
 MHC class II activates CD4 +T helper cells
 Present exogenous (eg bacterial) antigens
 CD4 T cells upregulate all immune functions
 MHC class II found only on cells that sample the
extracellular environment

9. Humoral Immunity
 The humoral immune response begins with the recognition of
antigens by naïve B cells.
 These cells then undergo a process of clonal expansion and
differentiation. Through this process, the B cell matures into
antibody secreting plasma cells, which secrete antibodies.
 Finally, as this response declines, a pool of memory cells remains
behind. If the body is re-exposed to the antigen, these memory
cells will recognize the antigen and respond much more quickly
and effectively.