INDUCTION MECHANISM OF HUMAN BLOOD CD8-CELL PROLIFERATION AND CYTOTOXICITY BY NATURAL-KILLER-CELL STIMULATORY FACTOR (INTERLEUKIN-12)( T)

Natural killer cell stimulatory factor (NKSF/IL-12) has been found to induce cytotoxic activity of human blood T cells. In the present study , the effect of NKSF on induction of cytotoxic CD8(+) T cells in the p resence or absence of monocytes was examined. Highly purified lymphocy tes (>99%) and monocytes (>90%) were isolated by centrifugal elutriati on from peripheral blood of normal donors. Then, CD8(+) cells were iso lated with antibody-bound magnetic beads from purified lymphocytes. Th e cytotoxicity of CD8(+) cells was measured by Cr-51 release assay for 4 h. NKSF enhanced the proliferative response of CD8(+) cells stimula ted with suboptimal concentrations of interleukin-2 (IL-2), but rather inhibited their proliferative and cytotoxic responses on stimulation with an optimal concentration of IL-2. NKSF stimulated CD8(+) cells to produce interferon gamma (IFN gamma) irrespective of the presence of added IL-2, and this effect was augmented by co-cultivation with monoc ytes. Blood monocytes upregulated induction of cytotoxic CD8(+) cells stimulated with NKSF alone, and this effect was abolished by addition of antibody against IFN gamma, but not of antibody against tumor necro sis factor alpha. Induction of NKSF-inducible cytotoxic CD8(+) cells w as inhibited by addition of transforming growth factor beta, but not o f IL-4. These observations suggest that in situ induction of NKSF-stim ulated cytotoxic CD8(+) cells may be regulated by complex cytokine net works, depending on the participation of monocytes.