Human B-cell growth and differentiation factors, and their effects on leukemic B-cells.

A wealth of data on B-cell growth and differentiation factors has been published recently, and so many different factors have been shown to act on B cells [1] that it is difficult to determine which, if any, of these factors are physiologically relevant. Initial models assumed that B-cell activation leads to an ordered expression of receptors for specific growth and then differentiation factors, but these now appear to be incorrect. Firstly, most of the factors with functional effects on B cells are not specific for cells of that lineage. IL2, ILl and IFNy have all been shown to have effects on B cells [1, 2]. Secondly, BSF-2 (B-cell differentiation factor BCDFy), which has recently been cloned [3], has been shown to activate mast cells and basophils, and to cause T-cell proliferation [4], while BCGF II acts as a differentiation factor for eosinophils [5]. The same lymphokine may also have different effects at different stages of B-cell differentiation. BSF-l acts on resting B cells to induce expression of class II antigens and prime cells for subsequent activation by anti-,u, but also acts on Staphylococcus A Cowan activated B cells to promote switching to production of the IgGl subclass [3]. Since BSF-l acts on resting B cells, it also appears that the assumption that antigenspecific activation is required before B cells