Partial characterization of a T cell-derived factor that suppresses the initiation of the humoral immune response in vitro.

Specific anamnestic stimulation of spleen cells from mice immunized 7 days earlier with horse erythrocytes (HRBC) generated the release of a soluble factor that was capable of suppressing the initiation of the in vitro primary gammaM immune response to sheep red blood cells (SRBC), as well as to the immunogen that elicited its formation. Moreover, the suppressive macromolecule (mol. wt yields to 34,000), derived from antigen-activated, HRBC-primed T lymphocytes (but not B cells), inhibited the secondary gammaM and gammaG anti-SRBC plaque-forming cell responses of SRBC-primed spleen cells. The active material was resistant to treatment with DNase and RNase, but was inactivated by protease (10 microgram/ml, 30 min) or exposure to mild heat (56 degrees, 30 min). The antibody initiation suppressor factor (AISF) was concentrated and partially purified by gel filtration, followed by poly-acrylamide gel electrophoresis.