[Molecular cloning of cDNAs encoding B-cell growth factors]

The proliferation and maturation of antigen-stimulated B cells are regulated by several soluble factors derived from macrophages and T cells. These soluble factors have been functionally divided into two groups; B-cell growth factor (BCGF) and B-cell differentiation factor (BCDF). However, this distinct classification and identification of B-cell factors should be reexamined after the recent cloning of cDNA encoding IgG1 induction factor (IL-4) from a 2.19 T-cell line. This factor induces not only an elevated IgG1 response in B cells activated by lipopolysaccharides but also hyper-Ia expression in B cells. IL-4 is identical to B-cell stimulating factor-1 (BSF-1) which induces DNA synthesis when given together with anti-IgM antibodies. Furthermore, this lymphokine has growth factor activities for both T and mast cells. Another well characterized B-cell factor is T-cell replacing factor (TRF). Although TRF was previously classified as a BCDF, a partially purified preparation of TRF was suggested to have BCGF II activity. The identity of TRF with BCGF II was proved by its cDNA cloning and the name IL-5 was proposed for this lymphokine.