AUTOANTIBODIES TO LACTOFERRIN AND HISTONE IN SYSTEMIC VASCULITIS IDENTIFIED BY ANTIMYELOPEROXIDASE SOLID-PHASE ASSAYS

We aimed at confirming the antigen specificity recognized by anti-neut rophil cytoplasm antibodies (ANCA) in patients presenting systemic vas culitis with anti-myeloperoxidase (MPO) activity on ELISA. Thirty-five consecutive patients with reactivity in anti-MPO ELISA and systemic m icroscopic vasculitides were tested in slot and Western blot analyses. Eleven of 35 sera exhibited binding in Western blot studies with the MPO preparation used in the ELISA: five sera bound at the size of MPO, but five sera reacted with a 78 kD species (p78) co-purifying with MP O, and one serum blotted both MPO and p78. Sequence analysis and antig en-specific assays including Western blot studies showed that p78 is l actoferrin. All anti-lactoferrin positive sera, but no anti-MPO positi ve sera, also exhibited anti-nuclear binding on HEp2 cells with specif icity for histone. We concluded that: (a) a subgroup of patients prese nting systemic vasculitis with false anti-MPO reactivity on ELISA had anti-lactoferrin antibodies; (b) anti-lactoferrin was associated with anti-nuclear activity with specificity for histone; (c) these patients had systemic vasculitis without histological evidence of immune compl ex deposition.