Plaque-forming cells in rabbits immunized with BCG bacilli.

Plaque-forming cells (PFC) in the regional lymph node, its efferent lymph, and the spleen of rabbits immunized with BCG were enumerated by localized hemolysis in gel, using sheep red blood cells coated with tuberculin protein. In the primary response, the maximal level of PFC production was reached at 5 days in the regional lymph node, and at 7 days in the spleen, whereas efferent lymphatic cells showed only a small number of PFC. Sharp peaks of PFC levels at 3 days were seen in the regional lymph node, spleen, and the efferent lymphatic cells in the secondary response. Blast cell outflow from the regional lymph node was maximal at 3 days in the secondary response as well as in the primary response. The relation between blast cell outflow and PFC production was discussed.