Effects of IL-7 and IL-2 on highly enriched CD56+ natural killer cells. A comparative study

IL-7 has been shown to induce low levels of lymphokine-activated killer cell (LAK) activity in bulk PBMC populations. We report here that immunomagnetically purified CD56+ cells from peripheral blood generated high LAK activity in response to IL-7. The LAK activity induced by IL-7 was comparable to, or slightly lower than, the LAK activity induced by IL-2. When analyzing cells from the same donor, no detectable LAK-generating effect of IL-7 was registered in the PBMC population, in contrast to a substantial effect in the CD56+ population. IL-2 induced 8- to 15-fold higher proliferative activity in CD56+ cells, relative to IL-7. At suboptimal concentrations of IL-2, IL-7 had a synergistic effect on the proliferation. IL-2-neutralizing antibodies did not abrogate the IL-7-induced proliferation or LAK generation. Both IL-7 and IL-2 induced comparable levels of 75-kDa TNFR expression, whereas IL-2R alpha expression was higher in IL-7-stimulated CD56+ cells. Low levels of TNF were produced in response to IL-7 at day 5, as opposed to a 50-fold higher TNF production in response to IL-2. No IL-2 or IL-6 production was detected. Our data indicate that IL-7 has profound and direct effects on CD56+ cells.