Specific modulation of antibody production in vitro by soluble mediators.

The 19S-PFC response to SRBC reaches a peak at 4 days. After this time, the number of 19S-PFC gradually decreases with a half-life of approximately 20 hours. The factors which influence this rate of decline of 19S-PFC after 4 days have been investigated. The decline is not the result of non-specific inhibitors in the tissue medium: medium harvested from cultures at the time of the peak PFC response can support another PFC response by fresh spleen cells. The survival of 19S-PFC in culture is a sensitive function of the number of specific T cells in the culture, since removal of T cells enhances the decline of PFC. Evidence is presented that a θ-negative cell with surface receptors for SRBC can specifically enhance the rate of decay of SRBC-specific 19S-PFC . This decay is mediated by an antigen-specific soluble mediator which cannot be absorbed by specific antigens. This factor is unlikely to be specific hyperimmune mouse IgG since addition of anti-SRBC IgG at 4 days has no affect on the rate of decay of PFC. Although the properties of the supernatant activity have not been characterized, it might be either an anti-receptor antibody or an antigen—antibody complex.