PRIMING INDUCES FUNCTIONAL COUPLING OF N-FORMYL-METHIONYL-LEUCYL-PHENYLALANINE RECEPTORS IN EQUINE NEUTROPHILS

The synthetic formylpeptide fMLP is widely used as a model chemoattrac tant and secretagogue for mammalian neutrophils. Despite possessing fM LP receptors, equine neutrophils do not produce superoxide anions in r esponse to fMLP and there is no inflammatory reaction in the horse whe n fMLP is injected intradermally. The functional capability of these r eceptors was investigated after pretreatment with recognized priming a gents, Purified neutrophils were pretreated with lipopolysaccharide (L PS), platelet-activating factor (PAF), or tumor necrosis factor alpha (TNF-alpha) and superoxide anion generation and shape clange quantifie d by lucigenin-dependent chemiluminescence (LDCL) and flow cytometry, respectively. LPS, TNF-alpha, and PAF pretreatment induced significant LDCL in response to fMLP; similarly LPS pretreatment was a prerequisi te for fMLP-stimulated neutrophil polarization in response to fMLP. Ho wever, LPS failed to induce fMLP-mediated chemotaxis of equine neutrop hils. These data indicate that equine neutrophil fMLP receptors are no t vestigial as previously thought but can trigger both respiratory bur st activity and cell polarization responses after priming.