Antibodies to interleukin-6 inhibit Schwann cell proliferation induced by unfractionated cytokines.

We have previously demonstrated that unfractionated cytokines induce proliferation of neonatal rat Schwann cells in vitro. Incubation of Schwann cells with natural or recombinant human interleukin-1 (IL-1) does not induce Schwann cell proliferation, but antibodies to IL-1 inhibit Schwann cell proliferation induced by unfractionated cytokines of human origin. In this study we investigated the effect of interleukin-6 (IL-6), another monokine, on proliferation of rat Schwann cells. Incubation of Schwann cells with recombinant (r) mouse IL-6 and two types of human rIL-6 did not induce proliferation of Schwann cells or of endoneurial fibroblasts. However, antibodies to rhIL-6 inhibited Schwann cell proliferation induced by unfractionated cytokines but had no effect on fibroblast proliferation. Addition of excess rhIL-6 to a mixture of unfractionated cytokines plus anti-rhIL-6 abrogated the inhibitory effect of the anti-rhIL-6. Therefore, IL-6 is a co-mitogen for neonatal Schwann cells in vitro.