Race differences in immunogenetic features and photosensitivity of cutaneous lupus erythematosus from the aspect of Japanese studies.

Skin lesions of collagen diseases are influenced by environmental triggers, such as UV light, and are variable in cutaneous lupus erythematosus (LE), such as systemic LE (SLE), chronic discoid LE (CDLE), subacute cutaneous LE (SCLE), and LE tumidus (LET). Although there are a few conflicting reports on photosensitivity in collagen diseases, many Japanese dermatologists feel there are photosensitivity differences in LE between Asians and Caucasians with SCLE and LET. To address this issue, we have carried out genetic studies of Japanese SLE and CDLE patients and reviewed the race differences in photosensitivity of cutaneous LE from Japanese studies. Human leukocyte antigen (HLA) studies in Japanese patients revealed that HLA-DRB1*1501 association was with CDLE and SLE. The association between HLA-Cw6 and CDLE was first reported in a Japanese population, and a HLA-A33-B44-DRB1*1302 haplotype showed a positive association in CDLE. However, these results are not compatible with those from Caucasian subjects. There are no significant associations among HLA studies, photosensitivity, and anti-Ro/SS-A antibodies in Japanese CLE patients. Photosensitivity will be a key factor to dissolve multifactorial complexes of LE etiopathogenesis. An axis of photosensitivity, anti-Ro/SS-A antibodies, and apoptosis via tumor necrosis factor-alpha is the best marker to verify the contribution of genetics in CLE patients. The incidence and degree of photosensitivity of SCLE and LET are much lower in Japanese than in Caucasians. This discrepancy may lead to investigations of CLE pathogenesis through global collaborations.