Significant enrichment of total IgM and IgG in rheumatoid arthritis (RA) synovia. Serum-normalized levels of (a) total IgM and (b) total IgG in extracts from osteoarthritis (OA) (n = 6) and RA (n = 11) synovial tissue obtained by arthroplasty or arthroscopic shaver biopsy and measured by enzyme-linked immunosorbent assay for antibodies of interest and albumin. GAPDH-normalized message for IgM (c) and IgG1 (d) heavy constant region as determined by quantitative real-time polymerase chain reaction in the same synovia as in (a) and (b). See Figure 1 legend for box plot definitions. Indicated P values were determined by Wilcoxon rank sum test. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; REU, relative expression units; SSI, synovial/serum index.