ACTIVATED EOSINOPHILS ELICIT SUBSTANCE-P RELEASE FROM CULTURED DORSAL-ROOT GANGLION NEURONS

This study was performed to test the hypothesis that activated eosinop hils or their secretory products can directly stimulate sensory neuron s to release their neuropeptides. Neurons derived from neonatal rat do rsal root ganglia (DRG), which synthesize and store sensory neuropepti des, were placed in primary cell culture and were exposed to eosinophi ls or their bioactive mediators. The resultant release of substance P (SP was measured by enzyme-linked immunosorbent assay and was expresse d as a percent (mean +/- SE) of total neuronal SP content. Eosinophils were isolated from human volunteers with a history of allergic rhinit is and/or mild asthma and were activated by incubation with cytochalas in B (5 mu g/ml) and N-formylmethionyl-leucyl-phenylalanine (FMLP, 1 m u M). Activated eosinophils [6 x 10(6)/ml, suspended in Hanks' buffere d salt solution (HBSS)] applied to cultured DRG neurons for 30 min inc reased basal SP release 2.4-fold compared with HBSS-exposed neurons (a ctivated eosinophils 11.10 +/- 2.48% vs. HBSS 4.59 +/- 0.99%; P = 0.00 2), whereas neither nonactivated eosinophils nor cytochalasin B and FM LP in HBSS influenced SP release. Additional cultured DRG neurons were exposed to soluble products made by eosinophils. Compared with SP rel ease under control conditions (2.37 +/- 0.34%), major basic protein (M BP) increased release in a concentration-related fashion (e.g., 3 mu M MBP: 6.23 +/- 0.67%, P = 0.006 vs. control), whereas neither eosinoph il cationic protein (3 mu M), eosinophil-derived neurotoxin (3 mu M), leukotriene Dq (500 nM), platelet-activating factor (100 nM), nor H2O2 (100 mu M) affected SP release. These studies demonstrate that activa ted eosinophils can stimulate cultured DRG neurons directly and sugges t that MBP may be the responsible mediator.