CD1 is a novel class of molecules which present non-protein antigens to T cells. The objective of this study was to evaluate the expression of CD1 in the skin and synovium of patients with psoriatic arthritis (PsA) in comparison with rheumatoid arthritis (RA) and osteoarthritis (OA).
Paired lesional skin (SK) and synovial membrane (SM) from four PsA patients, paired SK and SM from four RA patients, SM from eight RA and eight OA patients, and normal SK from four volunteers were studied using standard immunohistochemistry.
In all PsA and RA skin samples CD1-positive cells were abundantly detected both in the dermis and in the epidermis. However, in the 24 SM examined CD1-positive cells were rarely found. In one patient only with RA, a few CD1a-positive cells were found in the SM. CD1b was scarcely expressed in the lining layer (LL) of five SM and in very few cells in the sublining layer (SL) of 11 SM. CD1c was rarely expressed in the LL of six SM and in very few cells in the SL of 13 SM.
The paucity of CD1 in the PsA and RA synovium suggests that different subsets of antigen-presenting cells are involved in the pathogenesis of dermatitis and synovitis, respectively.