Localization of surfactant protein-D in the rheumatoid synovial membrane

Surfactant protein-D (SP-D) is a collectin, which plays an important role in airway protection and inflammation. The molecule has both pro- and anti-inflammatory capacities depending on its molecular size. Its involvement in joint diseases is largely unknown and the aim of this investigation was to study SP-D occurrence and distribution in the synovial membrane of patients with long-standing rheumatoid arthritis (RA) and osteoarthritis (OA). Six RA patients and six OA patients, who underwent total hip arthroplasty, were included in the study. Synovial tissue biopsies were obtained during surgery and subsequently prepared for immunohistochemistry. In this first, small-scale comparative study on the occurrence of SP-D in the synovial membrane of RA and OA, we report that SP-D was only present in the microvascular endothelium in subsynovial and pannus tissue and that the immunostaining was much stronger than in OA. This distribution pattern suggests that SP-D modulates RA inflammatory activities.