Regulation of natural killer cell activity by anti-I-region monoclonal antibodies

The effects of a monoclonal antibody directed against immune response gene products on mouse NK activity were examined. In vivo administration of an anti-I-A k antibody to C3H/He (H-2 k ) mice modulated their peritoneal cell (PC) and spleen cell (SC) natural killer (NK) activity against YAC-1 lymphoma target cells in vitro. No such effect was observed when BALB/c (H-2 d ) mice were treated with this antibody. Administration of anti-I-A k antibody to mice before and after infection with Toxoplasma or treatment with poly(I:C) leads to suppression of NK activity in comparison to NK activity of mice infected with Toxoplasma or injected with poly(I:C) alone. A similar treatment regimen with M5/114 antibody which reacts with I-A b , I-A d , I-E d , and I-E k molecules resulted in decreased NK activity in B10.D2 (H-2 d ) but not in B10.BR (H-2 k ) mice. Serum and cell culture supernatant interferon (IFN) concentrations were not altered as a result of anti-I-A k treatment. Removal of adherent cells did not restore NK activity of anti-I-A k -treated Toxoplasma -infected mice to levels obtained with mice infected with Toxoplasma. In contrast, depletion of Ly 2.1 + cells from nylon-wool nonadherent SC of mice treated with anti-I-A k antibody, before and after infection with Toxoplasma , resulted in restoration of NK activity to the same level as that observed in Toxoptasma -infected mice.