CHARACTERIZATION OF NATURAL-KILLER CYTOTOXIC FACTOR (NKCF) FROM CANINE NK CELLS

We investigated the presence of canine natural killer cytotoxic factor (NKCF). Canine natural killer (NK) cell-mediated cytotoxicity measure d by (51)chromium (Cr-51) release assay was found to be highest in the T-cell population, which was fractionated into the 35-40% Percoll fra ction by discontinuous gradient centrifugation. The cytotoxicity of NK CF in the culture supernatant showed a similar tendency to NK activity . Release of NKCF was rapid after contact with target cells, and reach ed a plateau in 60 min. The cytotoxicity of NKCF could be detected wit hin at least 15 min in coculture with CL-1 target cells, reaching a pl ateau in 60 min. We also characterized canine NKCF and found it to be a protein, which was stable against both heat and cold treatment. Thes e findings suggest that canine NK cells release NKCF immediately after recognition and binding to the target cell, and that NKCF plays an im portant role in canine NK-mediated cytotoxicity.