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.