Resistance to Mycoplasma pulmonis mediated by activated natural killer cells

Infection of C57BLl6J mice with Mycoplasma pulmonis (MP) enhanced NK cell function 3-7 days later, as detected by in vitro and in vivo assays. Moreover, spleen and lung cells of acutely infected C57BL/6J mice inhibited MP growth in vitro. The effectors were eliminated by treatment with anti-NK antibody in vivo and anti-asialo GMt serum or anti-3A4 antibody plus complement in vitro. Clearance of viable and radiolabeled MP from the lungs was also enhanced in acutely infected mice. Acutely infected mice with severe combined immunodeficiency (SCID) eliminated viable MP faster than did uninfected mice. Antibodies to interferon- (IFN-) impaired clearance of MP from the lungs of SCID mice and decreased their survival times. Activated NK cells can function in resistance to early stages of infection with MP. NK cells directly inhibit MP with secrete IFN-, which may activate macrophages or inhibit the growth of MP or both.