It should also be noted that the heterogeneity of the SFs from the “other disease” group was intended to show that the Id1 levels in OA SFs and SFs from a diverse patient population can be used together to verify that Id1 is uniquely elevated in RA SF, and can be correlated to RA SF CXCL16 expression. The gene discussed is CXCL16; the disease is rheumatoid arthritis.