Cell-mediated immune response to Shope fibroma virus-induced tumors in adult rabbits.

The parameters of cell-mediated immune responses of adult rabbits infected with Shope fibroma virus (SFV) were characterized by measurement of the size of local draining nodes, number of cells per lymph node, mitogen responses of lymphocytes, and kinetics of virus-specific cell-mediated lymphocytotoxicity (CML). In addition, the cytolytic effector population was characterized. After intradermal injections, tumors appeared within 3-4 days, reached maximum size in 10-12 days, and then regressed completely with 24 days. The size of local popliteal lymph nodes, in particular the diffuse cortex (paracortex), and the number of cells per node increased during tumor growth but then declined as the tumor regressed. Maximum specific CML to SFV-infected kidney cell monolayers (RK-13) occurred 10 days after inoculation of SFV and correlated with the initiation of tumor regression. Adult cytotoxic lymphocytes passed through nylon wool, and most of their activity was removed by treatment with antithymocyte globulin plus complement. Cytotoxic T-cells from SFV tumor-bearing rabbits killed only targets infected with SFV and not targets uninfected or infected with vaccinia virus. Therefore, T-cell-mediated virus-specific CML appeared as a major immune effector mechanism that correlated with tumor regression. However, antibody-dependent cell-mediated and NK cytotoxicity were also demonstrable. The presence of different cell-mediated cytotoxic mechanisms suggested a heterogeneity of effector mechanism.