Expression of myeloid related proteins (MRP) 8 and 14 and the MRP8/14 heterodimer in rheumatoid arthritis synovial membrane

Objective. Myeloid related proteins (MRP) 8 and 14 and the heterodimer MRP8 /14 are myeloid differentiation markers present on infiltratings tissue mac rophages in inflammation but not on resident tissue macrophages. We determi ned the pattern of expression of MRP8, MRP14, and the MRP8/14 heterodimer ( 27E10 antigen) in rheumatoid arthritis (RA) synovial membrane (SM). Methods. SM samples were obtained from patients with RA at joint replacemen t surgery or at arthroscopy and patients without joint disease (healthy sub jects) and immunostained for MRP8, MRP14, 27E10 antigen (MRP8/14 heterodime r), and CD68. Positive cell staining was measured by quantitative analysis. Results. SM from 8 patients with RA, including 7 who had paired samples fro m both adjacent to the cartilage-pannus junction (CPJ) and an area remote f rom the CPJ, and 2 healthy controls were analyzed. In RA, CD68+ cells accum ulated in greater numbers adjacent to the CPJ than remote from the CPJ [mea n +/- standard error of the mean (SEM) 488 +/- 103 and 256 +/- 76 cells/mm( 2), respectively; p = 0.01]. SM lining layer (LL) MRP8, MRP14, and 27E10 st aining was observed predominantly adjacent to the CPJ and only in patients with active disease. Minimal or absent LL MRP staining was observed in non- CPJ sections. Synovial sublining layer (SL) MRP8, MRP14, and 27E10 staining was also observed only in patients with active disease, but in contrast to the LL, SL staining was observed predominantly in sections remote from the CPJ. Conclusion. MRP antigens, representing activation markers on SM macrophages , were observed pre dominantly in the LL of sections adjacent to the CPJ sa mples. These original observations suggest altered activation and different iation of lining layer macrophages at the site of maximal cartilage destruc tion in RA.