B-Cell Activation

**Semantic type:** Cell Function

**Definition:** A set of events occurring in B lymphocytes following stimulation with cognate antigen. Crosslinking the B cell antigen receptor (surface immunoglobulin) leads to increased expression of MHC class II molecules, exit from the resting state (G0) into the G1 phase of the cell cycle, and in the case of a strong antigenic stimulus, proliferation.