Induction of helper T cells by antigen specific factor from macrophages

An immunostimulatory antigen specific factor (ASF) was found to be secreted by antigen-pulsed macrophages. Macrophages obtained from peritoneal exudate of C57BL/6 mice were pulsed with horse spleen ferritin (HSF). The PM10 ultrafiltration membrane-retained supernatant from the cultures of these macrophages was able to generate helper T cells when introduced into cultures of nylon wool purified T lymphocytes from spleens of C57BL/6 mice. The generation of helper T cells was measured by the cooperation between ASF-induced T cells and splenic B cells in the presence of trinitrophenyl (TNP)-HSF, and subsequently by the anti-TNP plaque forming cell (PFC) assay using TNP-coated sheep red blood cells. The number of PFC obtained from these cultures was significantly higher than the control (T cell cultures without ASF). Background levels of PFC were obtained when the T-B cooperation cultures were challenged with other haptenated antigens (e.g. TNP-BSA) instead of TNP-HSF. In addition, ASF from allogeneic macrophages was unable to facilitate helper cell induction. These results indicated that helper T cell induction by ASF is antigen specific as well as genetically restricted. When small amounts of ASF were injected into syngeneic mice without any adjuvant, specific helper T cells could be obtained from the spleens of these animals which showed that ASF is also active in vivo.