Human peripheral blood monocytes are susceptible to interferon-activated natural killer cells

Monocytes and lymphocytes from peripheral blood were tested for their susceptibility to the natural killer (NK) cell activity of allogeneic and autologous lymphocytes. Peripheral blood monocytes, but not lymphocytes, were sensitive to the cytotoxic activity of interferon (IFN) activated NK cells. Allogeneic as well as autologous monocytes were sensitive to NK activity, although the killing seemed to be more pronounced in allogeneic combinations. The cells expressing cytotoxic activity for blood monocytes were found to conform to the characteristics of NK cells in the sense that they were activated by IFN, as well as in the sense that they were contained in the same cell fraction as large granular lymphocytes.