Correlation of antibodies against bovine type II collagen (CII) and human CII. Scatter plot of the levels of IgG antibodies against human CII and bovine CII in sera of patients with rheumatoid arthritis (RA; n = 94), psoriatic arthritis (PsA; n = 33), osteoarthritis (OA; n = 31), and normal human serum (NHS; n = 93). There is a highly significant correlation between the levels of antibodies against human CII and bovine CII (R = 0.777, P < 0.001). The points represent for individual sera the number of standard deviations above the mean of normal sera for which the mean is 0. A serum is regarded as positive if it is more than three standard deviations above the mean (dashed lines).