Deep penetration of antibodies into the articular cartilage of patients with rheumatoid arthritis.

This study was conducted to determine the presence of immunoglobulin G (IgG) and albumin in deep layers of articular cartilage from patients with rheumatoid arthritis or osteoarthritis and from normal organ donors. Cartilage plugs were cut into 20-microns slices with a microtome and ten consecutive slices were pooled, dividing the specimen into 200 microns sections starting from the articular surface. Each pool was extracted overnight thrice with neutral buffer, thrice with 6 M guanidine hydrochloride, and then degraded with bacterial collagenase. IgG and albumin were quantified in each extract. From the surface and deep layers significantly more IgG and albumin were extracted from rheumatoid than from normal specimens, both with neutral buffer and with guanidine. In neutral buffer extracts the molar ratios of IgG to albumin were comparable from normal and rheumatoid specimens, with a molar excess of albumin. In contrast, the molar ratios of IgG to albumin in guanidine extracts from rheumatoid cartilages were significantly higher than in normal cartilages, and the IgG was in molar excess of albumin only in rheumatoid extracts. These results show for the first time that IgG has penetrated deep into the cartilage in rheumatoid arthritis and may contribute to the degradation of cartilage by inflammation.