Characteristics of lymphoblasts appearing in efferent lymph in response to immunization with vaccinia virus

Efferent lymphocytes collected from a cannulated lymphatic draining a single lymph node were studied for their cytotoxic activity following the injection of live vaccinia virus s.c. into the drainage site of the lymph node. Three days after the injection of virus, there was a 40-fold increase in the output of lymphoblasts from the regional lymph node. However, antigen-reactive cells, presumable T-helper cells, cytotoxic T lymphocytes (CTLs) and CTL precursors, were first detectable in efferent lymph during the fifth day after injection of virus. After a secondary challenge with virus, both lymphoblasts and antigen-reactive lymphocytes appeared earlier in efferent lymph, but lymphoblasts were still found well before the antigen-reactive cells. Efferent lymph cells were fractionated into a blast-enriched and a blast-depleted population of cells. Antigen-proliferating cells, CTLs and CTL precursors were each found to coenrich with the lymphoblast population. These findings indicate that much of the initial lymphoblast migration from the regional lymph node into efferent lymph after immunization consists of cells that do not specifically react to the injected antigen in vitro. Previous studies using allogeneic lymphocytes as the antigen have attributed both antigen-proliferating cell and CTL activity to the small lymphocyte population. In contrast, our studies on antigen-proliferating cells, CTLs and CTL precursors, after immunization with virus, suggest that, during the first 10-12 days following immunization, these cells are large lymphoblasts rather than small lymphocytes.