B lymphocyte ontogeny and immunoglobulin production.

In this paper we review different aspects of B cell development on the path from the proB cell to the memory B cell and the plasmocyte. Emphasis is given to the positive and negative selection effects mediated by the changing forms of the surface immunoglobulin (Ig) receptor under successive microenvironments. Positive selection is linked to lambda chain expression at the pro- and preB cell stage in fetal liver and bone marrow. Negative selection takes place when surface (s)IgM is being cross-linked by autoantigens before the immature B cell can leave, or after it has left, the bone marrow. After somatic mutation, major expansion becomes possible for B cells with high-affinity sIg receptors. This takes place in the germinal centres of the secondary lymphoid organs in the context of major histocompatibility complex (MHC) restriction and provided the necessary T cell help is given. Kinetic data on B cell replenishment in the rodent models are used to draw a schematic view of an established B cell repertoire.