Enhancement of T. lymphocyte functions by Fc fragments of immunoglobulin. II. Augmentation of the cell-mediated lympholysis response occurs through an Lyt-1+2- helper T cell.

Fc fragments derived from papain digestion of human IgG have the capacity to augment specific T cell-mediated cytolytic responses. The addition of Fc fragments to cultures containing nylon wool-purified effector and irradiated stimulator cells results in a significant enhancement of the cytotoxic response. Fc fragment-mediated enhancement is restricted to those responses in which the allogeneic differences between effector and stimulator populations encompass the H-2 I region. Significant enhancement of the CML response occurs when differences at H-2 K + I + D (B10 alpha B10.BR) and H-2 I (A.TH alpha A.TL) regions are employed. In contrast strain combinations in which only the H-2 D region (B10.A alpha B10.A(2R)) difference occurs no enhancement is seen. The cellular site of Fc adjuvant action in the CML response is the Lyt-1+2- helper T cell. This was concluded from the finding that Lyt-1+2- helper cells had to be present to obtain Fc-augmented CML responses. The substitution of Interleukin 2 for Lyt-1+2- helper T cells maintained the cytotoxic response, but these responses were not susceptible to the enhancing properties of Fc fragments. Moreover, to achieve enhanced cytotoxic response Fc had to interact only with the cell population.