Morphologic and phenotypic analysis of canine natural killer cells: evidence for T-cell lineage.

Canine natural killer (NK) activity and antibody-dependent cell-mediated cytotoxicity were studied utilizing a canine thyroid adenocarcinoma cell line and a lymphoblastoid cell line (CT-45S), respectively, as cell targets. Fractionation of peripheral blood mononuclear cells by Percoll discontinuous-gradient centrifugation resulted in a six- to sevenfold enrichment in large granular lymphocytes (LGL) in parallel with a twofold increase in NK activity (%specific lysis) in low-density fractions. Further enrichment in LGL (78 +/- 6%) and NK activity (threefold increase) was obtained by lytic treatment of low-density fractions 2 and 3 with monoclonal antibody WIG4. By means of cytolytic treatment with additional monoclonal antibodies the phenotype of canine NK cells was determined as Dly-1+, Dly-6+, 1A1+, E-11+, DT-2-, WIG4-. Some NK cells were also Ia+. NK activity was relatively radioresistant with 40% specific lysis even after irradiation with 40 Gy. Among the populations examined, the highest NK activity was found in peripheral blood mononuclear cells, followed by splenic mononuclear cells and bone marrow mononuclear cells. These results indicate that canine NK cells have the morphology of LGL, are relatively radioresistant, and express cell surface antigens suggesting a T-cell lineage.