Regulation of the immune response. II. Characterization of the cell population(s) involved in the Fc fragment-induced adjuvant effect.

Fc fragments derived from human and murine Ig have been shown to possess adjuvant properties. The spleen cell population(s) affected by the Fc fragments is the T lymphocyte. That Fc fragments do not act directly on the B lymphocyte was shown by the fact that in a system where T cell help was substituted for by TRF and using TI antigens, no adjuvant effect was observed. The adjuvant signal provided by the Fc fragments is needed early in the culture period, because it was reduced by approximately 50% when delayed by 24 hr. When the addition of Fc was delayed by 72 hr, the antibody response was not significantly increased over the culture that received antigen only.