Differential activation of signal transduction pathways mediating oxidative burst by chicken heterophils in response to stimulation with lipopolysaccharide and lipoteichoic acid

Toll-like receptors (TLRs) have been previously shown to mediate oxidative burst in chicken heterophils. This study was conducted to begin to map the molecular pathways that regulate TLR-mediated oxidative burst. Peripheral blood heterophils from neonatal chicks were isolated and exposed to known inhibitors of signal transduction pathways for either 20 min ( genistein, verapamil, or chelerythrine) or 120 min ( pertussis toxin) at 39 degreesC. The cells were then stimulated for 30 min at 39 degreesC with Salmonella enteritidis lipopolysaccharide (LPS) or Staphylococcus aureus lipoteichoic acid (LTA). The heterophil oxidative burst was then quantitated by luminol-dependent chemiluminescence (LDCL). Genistein ( a tyrosine kinase inhibitor), verapamil ( a calcium channel blocker), chelerythrine ( a protein kinase C inhibitor), and pertussis toxin ( a G-protein inhibitor) significantly reduced LPS-stimulated oxidative burst in chicken heterophils by 34, 50, 63, and 51%, respectively. Although genistein had a statistically significant effect on reducing LPS-stimulated LDCL biologically it seems to play only a minor role within the oxidative burst pathway. Heterophils stimulated with the gram-positive TLR agonist, LTA, activated a different signal transduction pathway since chelerythrine was the only inhibitor that significantly reduced (72%) LTA-stimulated oxidative burst. These findings demonstrate that distinct signal transduction pathways differentially regulate the stimulation of oxidative burst in avian heterophils. Pertussis toxin-sensitive, protein kinase C-dependent, Ca++-dependent G proteins appear to regulate oxidative burst of avian heterophils stimulated with gram-negative agonist LPS; whereas, a protein kinase C-dependent signal transduction pathway plays the major role activating the oxidative burst of avian heterophils stimulated with gram-positive agonists. The distinct differences in the response of heterophils to these two agonists illustrate the specificity of TLRs to pathogen-associated molecular patterns (PAMP)s.