Antibody-dependent killing of virus-infected targets by NK-like cells in bovine blood.

Natural killer (NK) cell lysis of target cells by an Fc receptor-mediated mechanism has not been conclusively demonstrated in cattle (Campos and Rossi, Vet. Immunol. Immunopathol. 8, 351-362, 1985), although it is well recognized in other species (Sulica et al., Nat. Immun. 14, 123-133, 1995). To resolve this problem, bovine peripheral blood mononuclear cells were completely depleted of adherent monocyte/macrophage type cells. The resulting enriched population of lymphocytes, was totally devoid of adherent monocytes, but contained up to 2% NK-like cells. On their own, this population had very low background levels of cytotoxicity for virus-infected target cells in 51chromium release assays, but following the addition of virus-specific antibodies, high levels of lysis were observed. This enhanced level of antibody-dependent cytotoxicity demonstrated that bovine NK-like cells can mediate killing of targets by an Fc receptor-mediated mechanism as has been demonstrated for NK cells from other species.