Triggering mechanism of B lymphocytes. II. Induction of ornithine decarboxylase in B cells by anti-immunoglobulin and enhancing soluble factor.

In vitro stimulation of rabbit lymphocytes with anti-immunoglobulin antibody (anti-Ig) induced ornithine decarboxylase (ODC) (EC4.1.1.17) in the cells. The enzyme activity reached the maximum at 8 hr after stimulation of the cell with antibody and returned to the unstimulated level after 20 hr. The optimum concentration of antibody to produce the maximum activity of ODC was 25 mug/ml, which was in the same range that required for the maximum production of IgG and the highest rate of DNA synthesis. ODC was again induced with soluble factor (SF) in the cells that had been previously treated with anti-Ig antibody for 24 hr. The treatment of the cells with anti-thymocyte serum and complement did not affect the activity of the enzyme induced by anti-Ig or by SF, indicating that enzyme induction was an event occurring in B cells and not in T cells. The addition of mitotic inhibitors, such as hydroxy-urea (HU) or cytosine arabinoside (Ara-C), to the culture with anti-Ig did not inhibit the production of ODC. The presence of cytochalasin-B with anti-Ig did not inhibit, but rather enhanced, the synthesis of ODC. On the other hand, the presence of HU or cytochalasin-B with soluble factor completely suppressed the induction ODC. These results suggested that intracellular events that trigger the induction of ODC by the interaction of Ig receptor with anti-Ig may be different from the events that induce the same enzyme triggered by SF.