Studies on the cellular requirements for the in vitro generation of a cell-mediated immune response to syngeneic ultraviolet light-induced tumors.

Syngeneic ultraviolet (UV) light induced tumors express antigens on their surface that cans evoke strong immune responses both in vivo and in vitro. The in vitro immune response is characterized by the generation of cytotoxic T lymphocytes (CTL) which, when mixed with tumor cells, are capable of effecting cell lysis. When the cellular requirements for the primary in vitro generation of tumor specific CTL were investigated, it was found that a macrophage-like accessory cell was extremely important in the generation of an optimal response. Significant numbers of macrophages were found to be present in UV induced tumors and, when separated from tumor cell in vitro were shown to be more effective as stimulating the in vitro generation of CTL than purified tumor cells. The in vitro generation of CTL in response to cultured (macrophage free) tumor cells was also greatly enhanced by the addition of normal peritoneal macrophages to the sensitization culture. High levels of CTL activity were also generated by the in vitro culturing of draining lymph node (DLN) cells from tumor-immunized mice for 4-days in the apparent absence of tumor antigen. This in vitro differentiation of CTL activity by DLN cells was a very radiosensitive process and involved high levels of proliferation. Both proliferation and differentiation of CTL activity in vitro was dependent upon the presence of an accessory cell in the DLN cell population. The accessory cell was shown to be resistant to gamma irradiation, adherent to nylon and glass wool columns, sensitive to treatment with anti-Ia antisera plus complement (C) and resistant to treatment with anti-Thy 1 antisera plus C. Antigen presentation did not appear to be required for effective cooperation between DLN lymphocytes and accessory cells from normal mice, although antigen presentation did occur when lymphocytes from normal mice were mixed with DLN accessory cells. The accessory cell Ia antigens were further evaluated by both absorbtion of anti-IaK antisera and the use of I-sub-region specific plus C. Absorbtion experiments demonstrated that removal of both I-A and I-E sub-region coded specificities from anti-IaK antisera was necessary to deplete the antisera of cytotoxic activity against DLN accessory cells. Antisera specific for the A, B, and J sub-regions were also effective at removing accessory cell activity from DLN cells. One of these antisera possessed activity against only specificity Ia.7 of the Ek haplotype, suggesting the expression of Ia.7 on the accessory cell. Antigens coding in the I-J sub-region could not be detected when using an antiserum with known anti-suppressor cell activity. These results suggest the expression of I-A and I-E sub-region coded antigens on the accessory cell and data is presented indicating that both antigens are expressed on the same cell. A discussion is presented dealing with potential mechanisms of accessory cell-lymphocyte interactions and the accessory cell Ia antigens in the generation of a tumor immune response.