In vivo and in vitro administration of interleukin 2-containing preparation reverses T-cell unresponsiveness in Mycobacterium bovis BCG-infected mice.

Mice infected with high doses of Mycobacterium bovis BCG (3 X 10(7)) showed a marked impairment of delayed-type hypersensitivity to PPD in vivo, and their splenic T cells failed to proliferate when cultured in vitro with concanavalin A or PPD. However, this state of unresponsiveness could be reversed both in vitro and in vivo by the administration of an interleukin 2 (IL-2)-containing preparation. IL-2 produced spontaneously by the gibbon lymphosarcoma T-cell line MLA-144 and T-cell-conditioned medium from a mixed lymphocyte reaction were able to increase DNA synthesis of splenic T lymphocytes from BCG-immunosuppressed mice cultured with concanavalin A or PPD. Furthermore, BCG-infected mice treated in vivo with at least 100 U of IL-2 showed a positive skin reaction to PPD, and their spleen cells were fully responsive in vitro. The reversal of BCG-induced immunosuppression was not observed when infected mice were injected with IL-2 preparations previously incubated with blast cells, a procedure known to remove IL-2 activity. These results indicate that the basis of BCG-induced unresponsiveness is a deficiency in the production of IL-2 rather than a lack of reactive T cells.