In vitro Ig heavy chain isotype suppression of spleen cells from immunized rabbits.

We tested whether purified antibodies (Ab) to immunoglobulin (Ig) heavy chain isotoypes could suppress immune Ig-secreting lymphocytes in vitro. Rabbit immune spleen cells (SpC) were treated with purified goat Ab to IgM (anti-μ Ab) or to IgG (anti-γ Ab) in vitro for 24 hr (Day 1). After this treatment, the SpC were washed and recultured to Day 5. The cells were again washed and then tested for Ig-bearing cells by a rosette forming cell assay and tested for Ab-secreting cells by the conventional plaque forming cell assay. In addition, the supernatant fluids were quantitated for secreted Ig by a radial immune hemolysis in gel assay. The number of Ig-bearing cells, the number of Ab-secreting cells and the amount of secreted b4 Ig decreased when “primary immune” SpC were pretreated with anti-μ but not when the SpC were pretreated with anti-γ Ab. Thus, SpC from rabbits injected once with SE were suppressed by anti-μ but not by anti-γ Ab. In contrast, SpC from rabbits injected several times with SE (hyperimmunized) were not suppressed by either anti-μ or by anti-γ Ab. This susceptibility of primary immune (IgM-secreting) SpC and resistance of hyperimmune (IgG-secreting) SpC to suppression may depend on the stage of B lymphocyte differentiation. That is, more differentiated cells such as IgG-secreting cells are insensitive to anti-μ and anti-γ Ab presumably due to lack of surface Ig molecules or for other reasons.