In vivo depletion of natural killer cell activity leads to enhanced multiplication of Mycobacterium avium complex in mice.

Earlier investigations have shown that murine natural killer (NK) cells inhibit the growth of fungal and bacterial pathogens in vivo and in vitro. In order to define the role of NK cells in Mycobacterium avium complex infection, in vivo depletion of NK cells by using anti-NK1.1 monoclonal antibody and conventional anti-asialo-GM1 antibody has been attempted. Repeated injection of 200 micrograms of anti-NK1.1 or 50 micrograms of anti-asialo-GM1 antibody effectively depleted NK activity in the spleens of C57BL/6 mice. The growth kinetics of M. avium complex over a period of 4 weeks showed that the colony counts in the spleens of the antibody-treated group were significantly (P less than 0.01) higher than those of the control group and compared well with those of the genetically NK cell-deficient C57BL/6 bg/bg mutant. The alternate strategy of in vivo stimulation of NK activity by poly(I:C) administration did not show a similar reduction in CFU in the spleen compared with the untreated control. The in vivo antibody depletion of NK activity provides direct evidence on the role of NK cells in the control of intracellular mycobacterial pathogens such as M. avium complex.