HLA and autoimmunity in scleroderma (systemic sclerosis)

Scleroderma or systemic sclerosis (SSc) has been associated with certain class II antigens of the major histocompatibility complex (MHC), including HLA-DR1, DR2, DR3, DR5, and DR52. In general, these earlier HLA correlations were weak and varied considerably among reporting centers and different ethnic populations. More recently, a variety of disease-specific autoantibodies have been discovered including anti-centromere, antitopoisomerase I, and a variety of anti-nucleolar antibodies. These specificities show little overlap among one another, and each are markers for certain clinical features of SSc. At the same time, molecular studies of the MHC have provided more accurate methods for defining specific HLA alleles. Now it is becoming clear that certain HLA class II alleles, especially HLA-DQ, are more strongly associated with autoantibody subsets of SSc than with the disease itself. For example, anticentromere antibodies are strongly associated with HLA-DQB1*0501 (DQ5), DQB1*0301 (DQ7) and other DQB1 alleles possessing a glycine or tyrosine residue in position 26 of the outermost domain. Anti-topoisomerase I antibodies occur in SSc patients with HLA-DQB1*0301 (DQ7), DQB1*0302 (DQ8), DQB1*0601 (DQ6 in Japanese), and other DQB1 alleles possessing a tyrosine residue in position 30. HLA-DQ alleles associated with these autoantibodies tend to be in linkage disequilibrium with the HLA-DR specificities previously associated weakly with SSc itself. Rare multiplex families with SSc also show these same HLA haplotypes co-segregating with autoantibody profiles in affected members. Thus, it appears that MHC alleles play a role in affecting the serological expression of SSc, and the implications of these recent findings are discussed.