Immunohistology studies of synovial tissue have demonstrated conflicting results, with some studies showing an increase in synovial B cell lymphoid aggregates, and T cell subsets in ACPA+ RA associated with development of more erosive disease, while other studies showed no differences in immune cell infiltrates, but did demonstrate increased synovial cytokine responses [11,12,13,14]. This evidence concerns the gene PRTN3 and rheumatoid arthritis.