Expression of major histocompatibility class II antigens on polymorphonuclear neutrophils in patients with Wegener's granulomatosis

Background. Wegener's granulomatosis is a systemic inflammatory disease of unknown etiology. Many studies suggest that autoimmune reactions are involv ed, and there is good evidence for the participation of immunocompetent cel ls. In that context, we examined the activation of polymorphonuclear neutro phils (PMNs) of patients with Wegener's granulomatosis. Methods. In a prospective study, the expression on the surface of PMNs of C D64 and of the major histocompatibility class II (MHC II) antigen was measu red by cytofluorometry in whole blood. The expression of those antigens was correlated to disease activity. Results. Up to 15% of the peripheral PMNs of patients with active disease e xpressed MHC II. Follow-up studies showed that expression correlated closel y with disease activity and that it decreased rapidly under immunosuppressi ve therapy. Expression of CD64 was seen in approximately 50% of the patient s, regardless of disease activity. Conclusion. MHC II expression on PMNs might serve as a novel diagnostic mar ker for active disease and appears to be suitable for monitoring immunother apy. Moreover, our data provide evidence that PMNs, which are normally MHC II negative, acquire MHC II antigens in the course of disease and may be an unrecognized function within the afferent limb of the immune response.