Properties of antigen-specific suppressive T cell factor in the regulation of antibody response of the mouse. II. In vitro activity and evidence for the I region gene product.

An antigen-specific suppressive T cell factor, which was extracted from carrier-primed T cells, was further characterized in an in vitro secondary antibody response. The factor was capable of suppressing secondary IgG antibody response of primed spleen cells when it was added to the culture together with relevant antigen. The suppressive T cell factor was not released from primed T cells by a short-term culture with antigen, but was kept bound to the membrane of the residual cultured cells, only the physical disruption of which can release the T cell factor. The target of the suppressive T cell factor was determined as being the helper T cell, since the factor did not exert any effect in the absence of the helper T cell with identical specificity to that of the factor. The suppressive activity was completely absorbed with alloantisera specific for products of the I region of H-2 complex, although various anti-immunoglobulin antisera failed to do so. Close analysis of the specificity of alloantisera capable of absorbing the suppressor molecule indicated that the suppressive T cell factor may, in fact, be an I region gene product probably coded for by genes in I-A and/or I-B (including I-E) subregions.