Development of T and B cells and their functional interactions.

The development of IgM-, IgG- and then IgA-bearing B lymphocytes is an orderly process occurring independently of antigens and T cells. T cells enhance antigen-induced B lymphocyte to plasma cell differentiation according to the hierarchy: IgA greater than IgG greater than IgM. T cells also exhibit antigenindependent and dependent stages of differentiation and a functional diversity, perhaps attributable to different classes of T cells. New evidence indicates the presence of a receptor on T cells for IgM antibody produced by B cells.