Induction of cytotoxic lymphocyte responses by antigen-specific helper factors.

Antigen-specific helper factors (ASHF) were purified by antigen-affinity chromatography from supernatants of long-term helper T lymphocyte (TH) lines. We have modified an established helper-dependent assay system to demonstrate the antigen specificity and H-2 restriction properties of ASHF in the induction of cytotoxic T lymphocyte precursors (CTLp). Antigen specificity is demonstrated by the binding of ASHF molecules only to nominal antigen, both during purification and in tests of functional activity. Our ASHF preparations do not contain any interleukin 2 (IL 2) activity. The ASHF, purified by antigen-affinity chromatography in the presence of Ca++, is defined as Ca++-sufficient ASHF, whereas ASHF purified on antigen-affinity columns in the absence of Ca++ is defined to be Ca++ deficient. Ca++-sufficient ASHF is not H-2 restricted (as defined by the phenotype of the ASHF-producing cells) in the recognition of nominal antigen or in its interactions with CTLp or adherent stimulator cells. In contrast, when the "complete" (Ca++-sufficient) ASHF is functionally dissociated into subunits by removal of Ca++, the "incomplete" antigen-specific subunit of ASHF (Ca++-deficient ASHF) is still H-2-unrestricted in its ability to bind nominal antigen, but requires products from syngeneic adherent cells to trigger CTLp. When adherent cells that are H-2 identical to the ASHF are provided in culture, the "incomplete" ASHF is able to trigger either syngeneic or allogeneic CTLp in an antigen-specific manner. We interpret the results of our experiments to suggest that an H-2-restricted molecular interaction occurs in CTLp induction by ASHF. An antigen-specific, TH-derived receptor appears to require association with Ca++ and self major histocompatibility complex (MHC)-encoded molecules to form a "complete" ASHF that is able to trigger CTLp in an apparently H-2-unrestricted manner.