Polymorphonuclear neutrophils in Wegener's granulomatosis acquire characteristics of antigen presenting cells

Background. Constitutive expression of major histocompatibility complex (MHC) class II antigens and of the co-stimulatory receptors CD80 and CD86 is restricted to professional antigen presenting cells. Polymorphonuclear neutrophils (PMN) of healthy donors are negative for those antigens. Our recent study, however, found that PMN of patients with active Wegener's granulomatosis acquired MHC class II antigens. Methods. To continue and extend the previous study results, PMN and monocytes of 60 patients with Wegener's granulomatosis, 24 patients with microscopic polyangiitis (MPA), 20 patients with acute bacterial infection, and 53 healthy donors were analyzed for the expression of MHC class II antigens as well as of CD80 and CD86. Moreover, induction on PMN of MHC class II expression was studied, as was antigen presentation as a possible functional consequence. Results. PMN of patients with acute, active Wegener's granulomatosis expressed MHC class II antigens, CD80 and CD86; on monocytes up-regulation of MHC class II was seen. In contrast, PMN of patients with inactive disease, or with relapse, patients with microscopic polyangiitis or with bacterial infections expressed neither MHC class Il, nor CD80 or CD86. PMN of healthy donors acquired these antigens when cultured in the presence of T cells or T cell-derived cytokines. The PMN were then able to present to T cell antigens in a MHC-class II restricted manner. Conclusion. During active disease, the PMN of patients with Wegener's granulomatosis acquire characteristics of antigen presenting cells, whereas the PMN of patients with MPA or bacterial infection do not. The finding reflects differences in the pattern of the respective inflammatory response and suggests new effector functions of PMN. Moreover, MHC class II expression on PMN could serve as a novel marker for active Wegener's granulomatosis.