Human granulocyte-macrophage colony-stimulating factor is a neutrophil activator.

The polymorphonuclear leukocyte (PMN), or neutrophil, is the major host defence cell protecting the body against invasion by bacteria and fungi. Products of oxidative metabolism mediate PMN microbicidal and tumoricidal activity but the mechanisms by which these pathways become activated are not well understood. We have previously described a human granulocyte-macrophage colony-stimulating factor (GM-CSF) of relative molecular mass (Mr) 22,000 that also inhibits neutrophil motility (NIF-T activity). Because of its direct action on granulocytes, this lymphokine is a candidate for a neutrophil-activating factor. We have studied the effect of GM-CSF/NIF-T on superoxide anion generation in response to the bacterial chemo-attractant N-formylmethionyl-leucylphenylalanine (f-MLP), and report here that PMNs preincubated with either purified natural GM-CSF or biosynthetic (recombinant) GM-CSF showed increased (as much as fourfold) superoxide anion production in response to f-MLP. These results indicate that human GM-CSF is a neutrophil-activating factor.