Thoracic duct cells and spleen cells were tested for their ability to restore the primary antibody response of X-irradiated rats to bovine serum albumin (BSA), sheep red blood cells (SRBC), horse spleen femtin (HSF), and Salmonella typhi flagella. Spleen cells were at least as efficient as thoracic duct cells in restoring the response to BSA, HSF, and Salmonella typhi flagella.

In further experiments thoracic duct cells lacking large dividing lymphocytes were tested for their ability to restore the primary response. Large lymphocytes were eliminated by the in vitro incubation of thoracic duct cells for 24 hr at 37°C or by treatment of thoracic duct cell donors with the mitotic inhibitor vinblastine sulfate 24 hr prior to cannulation of the thoracic duct.

Experiments with SRBC show that incubated cells and cells from vinblastine-treated donors are as efficient as normal cells in restoring the primary antibody response. On the other hand, experiments with HSF and Salmonella typhi flagella show that incubated cells and cells from vinblastine-treated donors are about five times less efficient than normal cells in restoring the response. Normal thoracic duct cells were more efficient than incubated cells but less efficient than cells from vinblastine-treated donors in restoring the early response to BSA.

The experimental findings indicate that the classes of thoracic duct lymphocytes which initiate the primary antibody response to SRBC differ from the classes which initiate the response to HSF and Salmonella typhi flagella, or BSA.

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