Increasing viral doses of H101 resulted in decreasing lymphocyte proliferation to Con A. B6 mice were infected with decreasing viral doses (1 × 101, 1 × 102, 1 × 103, 1 × 104, 1 × 105 pfu) of H101 by i.p. inoculation. Spleens were harvested on day 7 p.i., lymphocytes were isolated and stimulated in vitro with increasing concentrations of Con A (0.1, 1, 3, 10 µg/ml). The proliferative response was measured by 3H-thymidine incorporation for the last 16–18 hours of a 72 hour assay. The stimulation index (SI) was used for proliferation analysis, in which the mean of the experimental data was divided by the mean of the background for each culture condition. Mouse spleen cells were pooled for proliferation assays, therefore statistics were not performed.