Proliferative activity of autoimmune MRL mouse serum IgG to interleukin 3-dependent cell line through autocrine...

Serum of an autoimmune MRL/Mp-lpr/lpr (MRL/l) mouse supported the proliferation of interleukin 3 (IL-3)-dependent cell line, FDC-P2. This IL-3-like activity initially appeared at 1 month of age and increased with age. Females showed higher titers than did males. MRL/Mp-+/+ mouse sera also exhibited such activity, though somewhat later in life only in female. Other autoimmune mice, NZB, NZB/NZW F1, and BXSB, demonstrated no such activity in either males or females, young and old. The active component of MRL/l sera was shown to be IgG. F(ab')2 or Fc fragments of MRL/l-IgG lost such activity. Not all IL-3-dependent cell lines, however, responded to MRL/l-IgG. We subcloned MRL-IgG responding and nonresponding clones from FDC-P2 cells and both were still dependent to IL-3. Such nonresponding IL-3-dependent cell lines, however, could be stimulated by the culture supernatant of the responding cell line, FDC-P2/185-4, after being stimulated with MRL/l-IgG. In this culture supernatant, IL-3 was found, thus the existence of an autocrine system was suggested in the IL-3-dependent MRL/l-IgG responding cell line.