Different effect of LPS-induced macrophage factor on antibody responses to TI-1 and TI-2 antigens.

Effect of macrophage culture fluid (MF) on thymic independent (TI) antibody responses was examined. MF potentiated antibody responses of spleen cells to dinitrophenyl (DNP)-Ficoll and DNP-liposome, TI-2 antigens, but not to trinitrophenyl (TNP)-BA and TNP-LPS, TI-1 antigens. The enhancing effect of MF on the anti-DNP-Ficoll response was dose-dependent. Neither T cells nor macrophages were required for MF to exert the effect, suggesting that MF works on B cells directly. B cells modulated by MF in their antibody responses were indicated to be in mature B-cell subset for the following reasons: (i) the cells were in (CBA/N x BALB/c) F1 female but not in F1 male mice; (ii) the cells bore the receptors for C3 on their surface. MF was indicated to exert the enhancing effect on the antibody response by modulating the proliferation and/or early events in differentiation of B cells and not by promoting antibody secretion. The active component of the MF was indicated to be Interleukin 1.