Age-dependent change in a soluble factor responsible for Th-2 type of help in the indirect plaque-forming antibody response.

A carrier-independent type of helper activity for the indirect plaque-forming response was detected in the supernatant of spleen cell suspensions from primed mice. The potency of the factor increased during the adult life of the spleen cell donor. The factor(s) acted antigen nonspecifically and across the major histocompatibility complex. The ability of spleen cells to generate this activity was lost after treatment of primed cells with anti-Thy 1.2, anti-Lyt 1.2, or anti-Ly 7.2, in the presence of complement. The capacity to generate the activity depended on the presence of cells which adhered specifically to surfaces coated with the sensitizing antigen. The production of factor(s) involved cooperation of nonadherent T cells from primed old animals and adherent cells from unprimed donors; the age-dependent change in factor-production did not depend on the age of the donor of adherent cells.