B-lymphocyte regulation of the immune system. III. Preparation and characterization of rabbit antibodies that inhibit the biological activity of the lymphokine, B-cell-derived enhancing factor (BEF).

Antibodies that inhibit the biological activity of B-cell-derived enhancing factor (BEF) were produced in a rabbit immunized with BEF obtained from a non-immunoglobulin-producing B-cell line. Immunoglobulin G (IgG) fractions purified from the preimmune or the immune rabbit serum were compared by testing for their capacity to inhibit regulatory activities of BEF. It was found that the enhancing activity exerted by BEF on the in vitro antibody response to sheep red blood cells was inhibited when anti-BEF IgG was incorporated in the cultures. Moreover, anti-BEF IgG abolished the inhibitory activity exerted by BEF on the expression of Fc receptor by lymphoid cells. Comparable concentrations of preimmune IgG were ineffective in inhibiting BEF activity. The passage of supernatant fluid containing BEF activity through an anti-BEF IgG-coupled Sepharose column yielded an 84-fold purified product that exhibit BEF immunoregulatory properties. These results will accelerate further studies aimed at better characterization of the BEF molecule(s).