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Proliferation and maturation of antigen-stimulated B cells are regulated by several soluble factors derived from macrophages and T cells. These soluble factors are functionally divided into two groups: B-cell growth factor (BCGF), thought to be involved in B-cell proliferation; and B-cell differentiation factor (BCDF), responsible for maturation of activated B cells into immunoglobulin-secreting cells. This classification needs to be re-examined in the light of the recent cloning of complementary DNA encoding IgG1 induction factor (interleukin-4, IL-4) from the 2.19 mouse T-cell line. Recombinant IL-4 has BCGF and BCDF activities and affects B cells, T cells and mast cells (refs 7, 8; our unpublished data). Another well-characterized B-cell factor is T-cell replacing factor (TRF), which, when secreted by the murine T-cell hybridoma B151K12, is defined by two activities: induction of IgM secretion by BCL1 leukaemic B-cell line; and induction of secondary anti-dinitrophenol (DNP) immunoglobulin G (IgG) synthesis in vitro by DNP-prime B cells. Although TRF from B151K12 was classified as BCDF, purified TRF has BCGF-II activity. To elucidate the molecular properties of TRF we isolated cDNA encoding TRF from the 2.19 T-cell line and report here the structure and multiple activities of this lymphokine.

An actinomycete strain No. Q996-17 produced a novel compound, epoxomicin, which exhibited in vivo antitumor activity against B16melanoma. Structural studies indicated that it is a newmember of the epoxy-jS-aminoketonegroup, and is closely related to eponemycin.In our continuous search for antitumor agents showing specific activity against B16 murine melanoma, an unidentified actinomycete strain No. Q996-17 was found to produce a new compound epoxomicin. It wasextracted by rc-butanol from the fermentation broth and purified by various chromatographies. Structural studies revealed that epoxomicin has an epoxy-^-aminoketone moiety in the structure and is a newmemberof the eponemycin^group. Epoxomicin exhibited strong in vitro cytotoxicities against various tumor cell lines, whereas it did not exhibit anti-bacterial and anti-fungal activities. It showed strong in vivo inhibitory activity against B16 melanoma but moderate activity against P388 mouse leukemia.

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