Antineutrophil cytoplasmic autoantibodies (ANCA) recognizing a recombinant myeloperoxidase subunit

Sera from 76 patients with diverse vasculitis, systemic lupus erythematosus (SLE) and hydralazine-induced lupus (HiL) were analysed by ELISA for their reactivity with native, reduced or urea-denatured MPO, respectively, as well as with bacterially expressed heavy and light subunits of MPO. All sera (n = 20) recognizing native MPO showed a positive reaction with reduced MPO, while 12 recognized the denatured protein. Most of the linear epitopes are located in the light subunit, since 9 MPO-positive sera recognized significantly the bacterially expressed, denatured light subunit, while only one serum recognized the bacterially expressed heavy subunit purified under denaturing conditions.