Inhibition of microglial egress in excised ganglia by human interleukin 10: Implications for its activity in invertebrates

We studied the effects of recombinant human interleukin-10 (IL-10) on inver tebrate immunocytes and microglia. The present report demonstrates that the spontaneous activation of invertebrate immunocytes can be specifically inh ibited by recombinant human IL-10. Induced immunocyte activation by fMLP ca n also be significantly diminished by IL-10. This inhibition becomes appare nt over hours and causes ameboid cells to become round and nonmobile. Furth ermore, Mytilus edulis pedal ganglia maintained in culture, over the course of 24 hours, emit microglia. IL-10 significantly reduces this microglial e gress, an action that can be diminished by concomitant exposure of the exci sed ganglia to an antibody specific to IL-10 as well as IL-10. The anti-IL- 10 alone is without effect. Active-ameboid microglia that egress become rou nd and inactive following IL-10 exposure, an action prevented by anti-IL-10 . Lastly, a substance immunoreactively similar to human IL-10 can be detect ed in pedal ganglia homogenates. Taken together, and since the immunocytes and microglia are responding to IL-10, it implies that an IL-10-like substa nce could be present in invertebrates. In conclusion, the study demonstrate s that both invertebrate immunocytes and microglia respond to IL-10, sugges ting an early evolution of this generally inhibitory cytokine.