Electron microscopic morphology of immunoglobulin aggregates and their interactions in rheumatoid articular collagenous tissues.

Immunoelectron microscopy for IgG and IgA was combined with plain electron microscopy and light microscopy to study a variety of articular collagenous tissues from 14 cases of classic rheumatoid arthritis. Numerous extensive aggregates of IgG and IgA positive material were found widely spread in locations that coincided with immunofluorescent staining for these immunoglobulins and B1c. This Ig positive material is thought to represent deposits of immune complexes. As great and greater amounts were seen in fibrocartilage menisci as in hyaline cartilage. A single specimen of disease tendon was also positive. Severe pathologic changes of the matrix characterized by loss of normal morphology, alterations in collagen, and overall reduced density were observed in regions of aggregate deposition with a consistent replacement and disappearance of collagen in the locale of the aggregates themselves. Polymorphonuclear cells in regions of degraded hyaline and tendon matrix were seen to have phagocytosed aggregates. These data give some credence to a direct role of immune aggregates in rheumatoid arthritis articular collagenous tissues in disease pathogenesis.