Immune Memory

When a pathogen enters the body, a rare naive B cell with matching surface immunoglobulin binds antigen, then receives T helper co-stimulation. In germinal centers, the selected clone undergoes somatic hypermutation (AID enzyme mutates V regions at ~10⁻³ per base per division — 10⁶× normal) and iterative selection for higher affinity. The result: exponentially tighter antibodies and long-lived memory B cells that respond to re-exposure within hours instead of weeks.