B cell tolerance and autoimmunity.

Self-tolerance is induced in B cells at various maturational stages by diverse self-antigens B cell tolerance involves multiple mechanisms, ie. clonal deletion, clonal anergy, receptor editing and maturation arrest. The mechanism utilized for self-tolerance depends on both the maturational stage of B cells and the molecular nature of the self-antigens. B cell tolerance is abrogated by various mechanisms such as defects in inhibitory co-receptors, overexpression of CD19, T cell help and defects in the death receptor Fas (CD95). Since all of these molecules regulate B cell apoptosis mediated by either the antigen receptor or Fas, B cell apoptosis may play a role in the induction and maintenance of B cell tolerance. Moreover, environmental factors such as intestinal lipopolysaccharide also play a role in the breakdown of B cell tolerance.