Activation of polyclonal antibody responses by a synthetic serum thymic factor (FTS) in CBA/N mice.

A synthetic serum thymic factor (FTS) augmented the lipopolysaccharide (LPS)-induced polyclonal B-cell responses in vitro of CBA/N mice and their F1 hybrids having an X-linked B-cell defect. For this augmentation, FTS should be injected in vivo. Splenic B cells derived from FTS-treated mice with the CBA/N defect were receptive to T-cell help from normal or immunodeficient mouse T cells. Thus, the inability of B cells from mice with the CBA/N defect to accept T -cell help may not be caused by an intrinsic T-cell defect, but by a functional B-cell defect that can be corrected by treatment with FTS in vivo. Spleen cells from ATXBM CBA/N mice treated with FTS 3 weeks after cell transfer did not increase the B-cell response. B cells from FTS-treated male F1 mice with the CBA/N defect still have characteristics of neonatal mouse B cells as revealed by inhibition with antimouse Ig and anti-Ia sera. These findings suggest that FTS may act on generation of a B-cell acceptor for T -cell help, rather than on the maturation of a B-cell subset.