GM-CSF enhances LTB₄ release by monocytes stimulated with type III group B streptococcus (GBS)

LTB₄ and IL-8 are the predominant chemoattractants released by monocytes in response to GBS, with LTB₄ predominant early (4h) and IL-8 predominant later (24h). Granulocyte-macrophage colony stimulating factor (GM-CSF) has been shown to decrease mortality in a neonatal rat model of GBS sepsis. We hypothesized that GM-CSF would enhance chemoattractant release by monocytes exposed to GBS. Adult peripheral blood monocytes were allowed to adhere in 24 well plates, 106 cells/well. Type in GBS were added (inactivated, 10⁸ CFU/well) with or without GM-CSF. Supernatants were harvested at 4 and 24h and assayed for LTB₄ by RIA and IL-8 by ELISA. IL-8 values were equivalent with or without addition of GM-CSF. LTB₄ results at 4h, in pg/ml, (mean±SEM, n=4-5)are: GM-CSF, U/ml no GBS +GBS 0 124±78 423±67 25 261±78 631±47*250 262±71 656±51*2500 189±64 855±82*significant by ANOVA at 95% vs. GBS w/o GM-CSF GM-CSF significantly enhanced LTB₄ release by monocytes stimulated with GBS but IL-8 release was unaffected. This suggests that LTB₄ and IL-8 release are differentially regulated. We speculate that GM-CSF may be beneficial in GBS sepsis, enhancing early recruitment of neutrophils.