BCG-activated NK cells regulate the antibody response to SRBC and restore immune reactivity to PPD in BCG-infected mice

C57B1/6 mice show a significant increase in the number of natural killer (NK) cells in the peritoneal cavity, four days after intraperitoneal infection with Mycobacterium bovis strain BCG. Cell transfer experiments demonstrated that BCG-induced NK cells are able to depress the induction of antibody response to an unrelated antigen (i.e., sheep red blood cells) in recipient mice. The involvement of macrophages, B and T cells in the phenomenon was ruled out by using different purification steps. In addition, BCG-induced NK cells were shown to be able of partially restoring the DTH response to PPD in recipient mice that were anergic to the latter antigen as a consequence of intravenous infection with large doses of BCG.