Detection of anti‐myeloperoxidase and anti‐elastase antibodies in vasculitides and infections

SUMMARY Autoantibodies that produce a perinuclear pattern on indirect immunofluorescent examination of ethanol‐fixed neutrophils (pANCA) are found in about half of all cases of microscopic polyarteritis. These antibodies are often directed against myeloperoxidase or elastase and we have developed sensitive reproducible ELISAs for their detection and study. Seven sera from 19 patients with microscopic polyarteritis or segmental necrotizing glomerulonephritis contained anti‐myeloperoxidase or anti‐elastase antibodies or both. In contrast, only one of 18 sera from patients with Wegener's granulomatosis, where the pattern of immunofluorescence is predominantly cytoplasmic, had anti‐myeloperoxidase antibodies and no anti‐elastase antibodies were detected. Using sera from patients with microscopic polyarteritis, both anti‐myeloperoxidase and anti‐elastase antibodies were demonstrated to be of high affinity. There was no immunoglobulin class, subclass or light chain restriction noted. Anti‐myeloperoxidase and anti‐elastase antibodies were also found occasionally in anti‐glomerular basement membrane disease, mixed connective tissue disease, systemic lupus erythematosus, post‐streptococcal glomerulonephritis and atypical pneumonia. In further studies these antibodies were not associated with other lung infections, although anti‐elastase antibodies were noted in one of 14 sera positive for ASOT that were tested. Anti‐myeloperoxidase antibodies were found more frequently than anti‐elastase antibodies and these antibodies were occasionally present together. In addition some sera with pANCA had neither anti‐myeloperoxidase nor anti‐elastase antibodies. The target molecules in these cases remain unclear.