Absence of immunoglobulins in rheumatoid cartilage-pannus junctions

Immune complexes (IC) present in the superficial region of rheumatoid articular cartilage may be an important factor in the invasion of the cartilage by pannus. The presence of such IC at the cartilage-pannus junction in rheumatoid articular cartilage invaded by pannus was investigated by using immunoelectron microscopy with horseradish peroxidase anti-human immunoglobulin (Ig). It was observed that, although the pannus-free surface of the cartilage contained easily detectable deposits of Ig, the areas covered by pannus failed to show any Ig in the 5 5 patients studied. This was true even in areas immediately adjacent to the advancing edge of the pannus which presumably had only recently been invaded by the granulation tissue. These results were confirmed by fluorescent antibody ultraviolet microscopy. It was concluded that rheumatoid pannus invasion of the free cartilage surface containing trapped IC results in the disappearance of such complexes.