Figure 1.

Inhibition of MLR proliferation but not of cytotoxic activity against mouse fibroblasts by MV infection. For primary stimulation, cotton rats were injected i.p. with mouse spleen cells (C3H strain), and 4 weeks later their spleen cells were stimulated in vitro by cocultivation with mitomycin C-treated mouse spleen cells (MLR). The number of living cells was determined by trypan blue exclusion on day 5 of culture. From 3 × 10⁷ spleen cells per original culture in controls, 2.7 ± 0.8 × 10⁷ cells were recovered; in animals infected with MV before the primary stimulation, 1.4 ± 0.1 × 10⁷ cells were recovered; and from animals infected before the secondary stimulation, 1.3 ± 0.2 × 10⁷ cells were recovered (average of five animals per group ± SD). In addition, [³H]thymidine incorporation was measured in cpm ± SD (A, representative of four experiments) and the lytic activity of T cells in was measured in percentage of lysis ± SD (B). Cytotoxic T cells from noninfected animals (squares) and animals infected before the primary (circles) or secondary (triangles) stimulation were tested against mouse (L929 cells, open symbols) and cotton rat fibroblasts (solid symbols). YAC 1 cells that were lysed by cotton rat natural killer cells (data not shown) were never lysed above background. No consistent difference between cultures from infected and noninfected animals was detected in five separate experiments.