The presence of lymphoid aggregates in rheumatoid arthritis (RA) synovia is associated with elevated synovial autoantibody levels. Serum-normalized levels of (a) RF-IgM and (b) anti-CCP IgG in extracts from RA synovia with (Aggr, n = 8) or without (No aggr, n = 17) lymphoid aggregates. Tissues were obtained by arthroplasty or arthroscopic shaver biopsy, and extracts were analyzed by enzyme-linked immunosorbent assay for antibodies of interest and albumin. See Figure 1 legend for box plot definitions. Indicated P values were determined by Wilcoxon rank sum test. anti-CCP, anti-cyclic citrullinated peptide; RF-IgM, rheumatoid factor of the IgM subtype.