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 involved, and there is good evidence for the participation of immunocompetent cells. In that context, we examined the activation of polymorphonuclear neutrophils (PMNs) of patients with Wegener's granulomatosis. Methods. In a prospective study, the expression on the surface of PMNs of CD64 and of the major histocompatibility class II (MHC II) antigen was measured 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 expressed MHC II. Follow-up studies showed that expression correlated closely with disease activity and that it decreased rapidly under immunosuppressive therapy. Expression of CD64 was seen in approximately 50% of the patients, regardless of disease activity. Conclusion. MHC II expression on PMNs might serve as a novel diagnostic marker for active disease and appears to be suitable for monitoring immunotherapy. 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.