Inhibition of receptor-dependent and receptor-independent generation of the respiratory burst in human neutrophils and monocytes by human serum IgA.

An important feature of the role of IgA in protection against infection and disease at the level of the mucosal surfaces might be the elimination of pathogens without induction of a strong inflammatory reaction. In the present study we addressed the question whether IgA has a regulatory effect on the generation of reactive oxygen intermediates in human neutrophils and monocytes (i.e. the respiratory burst). Cells were stimulated with heat-inactivated Haemophilus influenzae type b or phorbol myristate acetate, stimuli known to use different recognition structures or signal transduction pathways. Concentrations of IgA as low as 10 mg/L significantly inhibited the receptor-dependent Haemophilus influenzae-induced respiratory burst in granulocytes, as assessed by measuring luminol-enhanced chemiluminescence. Furthermore, IgA had a dose-dependent inhibitory effect on the receptor-independent induction of the respiratory burst, as examined by flow cytometry in monocytes and granulocytes activated with phorbol myristate acetate. Our results therefore indicate that inhibition of receptor-ligand interaction is not a sufficient explanation for the IgA-mediated modulation of the respiratory burst in human phagocytic cells. In addition, IgA might directly regulate the activation of the respiratory burst at the level or downstream of protein kinase C activation. By modulating the release of mediators of inflammation such as reactive oxygen intermediates, the inflammatory response could be down-regulated at the level of the mucosal surfaces, thereby preventing the development of sequelae of an exaggerated inflammatory response potentially leading to local or systemic pathology.