Tumour necrosis factor-α potentiates CR3-induced respiratory burst by activating p38 MAP kinase in human neutrophils

CR3 and Fc gamma Rs are the main receptors involved in the phagocytic process leading to engulfment and killing of microbes by production of reactive oxygen intermediates (ROI) and degranulation. Various inflammatory mediators, such as tumour necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS), are known to prime neutrophils leading to increased bactericidal responses, but the underlying mechanism of priming has only been partially elucidated. The purpose of this study was to investigate how TNF-alpha primes neutrophils for subsequent stimuli via either CR3 or Fc gammaR. The receptors were specifically activated with pansorbins (protein-A-positive Staphylococcus aureus) coated with anti-CR3, anti-Fc gamma RIIa, or anti-Fc gamma RIIIb monoclonal antibody. Activation of neutrophils with these particles resulted in ROI production as measured by chemiluminescence. Anti-CR3 pansorbins induced the most prominent ROI production in neutrophils. TNF-alpha potentiated the CR3-mediated respiratory burst but had little effect on that mediated by Fc gamma Rs. The priming effect of TNF-alpha on CR3-mediated ROI production is associated with an increased activation of p38 MAPK as well as tyrosine phosphorylation of p72(syk). Pretreatment of neutrophils with the inhibitors for p38 MAPK and p72(syk) markedly suppressed the respiratory burst induced by CR3. Furthermore, TNF-alpha induced about a three-fold increase in the expression of CR3 in neutrophils, an effect which is blocked by the p38 MAPK inhibitor. Taken together, these results showed that TNF-alpha potentiates the CR3-mediated respiratory burst in neutrophils not only by triggering a p38 MAPK-dependent up-regulation of CD11b/CD18 but also by modulating the signalling pathways.