In vitro modulation of canine polymorphonuclear leukocyte function by granulocyte-macrophage colony stimulating factor

Granulocyte-macrophage colony stimulating factor (GMCSF) promotes the growth of granulocytes and macrophages from undifferentiated bone marrow cells and modulates the oxidative responses of polymorphonuclear leukocytes (PMN) to endogenous chemoattractants. We found that, in vitro, naturally occurring glycolsylated human GMCSF does not disturb the resting canine PMN membrane potential, may attentuate PMN oxidative responses to PMA, and is, to a small degree, chemotaxigenic. GMCSF, however, inhibits PMN chemotaxis to zymosan-activated plasma (ZAP). Compared to temperature controls, GMCSF (1-100 U/ml) produced up to 1.5-fold increases in H2O2 production after 15 minutes, while phorbol myristate acetate (PMA) treated cells increased H2O2 production 8-12-fold after 15 minutes. Preincubation of cells with GMCSF (1-100 U/ml) prior to PMA stimulation significantly reduced the H2O2 levels induced by PMA. H2O2 production was inhibited up to 15% after 15 minutes of GMCSF preincubation and up to 40% after 60 minutes of preincubation. As a chemotaxigenic agent, GMCSF (10-1000 U/ml) was able to elicit 49%-102% increases in quantitative cellular migration, compared to random migration. Total cellular chemotaxis to GMCSF was less than 30% of the response to ZAP. Preincubation of PMNs with GMCSF for 15 minutes significantly inhibited ZAP-induced cellular migration. Human GMCSF does not appear to activate canine PMN in vitro and may actually down-regulate PMN inflammatory responses.