Immunological characterization of heterochromatin protein p25beta autoantibodies and relationship with centromere autoantibodies and pulmonary fibrosis in systemic scleroderma.

Anticentromere antibodies (ACA) are immunological markers for the subset of systemic scleroderma with the symptoms calcinosis cutis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia (CREST). In Western blotting, some ACA-positive sera also recognize a doublet of 23 kDa (p23) and 25 kDa (p25) in addition to centromere protein antigens A (17 kDa), B (80 kDa), and C (140 kDa). Two forms of p25 have been shown to be human homologues of Drosophila heterochromatin-associated protein HP1. One form of p25 (p25beta) which was recently cloned in this laboratory was used to evaluate anti-p25beta antibody response in scleroderma sera. Of 318 scleroderma sera 42 had ACA (13.2%), and 16 of the 42 sera (38%) had anti-p25beta antibodies. On the other hand, 5 of 276 ACA-negative sera (1.8%) showed anti-p25beta antibody response, demonstrating that anti-p25beta antibody is significantly associated with the ACA response (P < 10[-8]). Clinically the anti-p25beta response was significantly associated with the CREST syndrome. Fourteen (36.8%) of 38 CREST patients compared to seven (2.5%) of 280 patients with other forms of scleroderma were anti-p25beta antibody positive (P < 10[-8]). The 14 CREST patients with anti-p25beta antibodies had significantly more interstitial lung disease than those without anti-p25beta antibodies (P < 0.003). There was also a tendency to increased liver involvement. Two dominant autoepitopes in p25beta were determined by Western blotting using p25beta recombinant fragments. In immunofluorescence C-terminal specific antibodies showed staining of heterochromatin, but N-terminal specific antibodies showed no staining. Interestingly, the majority of sera reacted preferentially with one or the other of the two dominant autoepitopes.