B cell dependence on and response to accessory signals in murine lupus strains.

Abstract

B cell hyperactivity, a feature common to all lupus-prone murine strains, may be caused by hyperresponsiveness to, overproduction of, or bypassing of certain signals required for B cell activation, proliferation and differentiation. The responses of B cells from 3 lupus-prone strains of mice (BXSB males, MRL and NZB/W females) and normal strains were compared in a number of assays for which 2 or more signals are required to obtain a response. In medium to low density cultures of B cells from BXSB and NZB/W but not MRL/l lupus mice, the cells'' proliferation induced by bacterial lipopolysaccharide (LPS) or anti-.mu. antibody was much higher than that of B cells from normal controls. At low B cell density, polyclonal activation by these substances and subsequent Ig secretion were dependent on accessory signals present in supernatants of concanavalin A-treated normal lymphocytes (CAS) or on the MRL/l proliferating T cell-derived B cell differentiation factor (L-BCDF) in both lupus-prone and immunologically normal mice. The responses of B cells from BXSB and NZB/W, but not MRL/l, mice to these accessory signals were higher than those of normal mice. Ig synthesis by fresh B cells of BXSB and NZB/W mice cultured in the absence of mitogens but in the presence of CAS or L-BCDF was higher than by similar cells from other strains, suggesting an increased frequency of B cells activated in vivo in these 2 autoimmune strains of mice. The patterns of IgG subclass secretion in response to LPS (without added CAS or L-BCDF) were abnormal in all lupus strains, with a predominance of IgG2b and/or IgG2a,and low levels of IgG3, contrary to normal B cells for which IgG3 synthesis predominated. IgG1 synthesis in vitro by autoimmune and normal B cells alike was highly dependent on T cell-derived soluble mediators. Antigen-specific responses to SRBC [sheep red blood cell] in vitro of B cells from all lupus strains, like those of B cells from normal strains, required a minimum of 3 signals (antigen, LPS, T cell-derived antigen nonspecific helper factors). Once triggered, B cells of BXSB and NZB/W mice gave higher responses than those of the other strains. B cells of lupus mice have signal requirements similar to those of normal mice. B cells of BXSB and NZB/W, but not MRL/l, lupus mice hyperrespond or process some accessory signals abnormally.