A mononuclear phagocyte subset associated with cell necrosis in rheumatoid nodules: identification with monoclonal antibody 5.5.

A subset of mononuclear phagocytes identified by mAb 5.5 has been found within rheumatoid subcutaneous nodules. These cells appear to be derived directly from blood-borne monocytes. They form a variable proportion of the mononuclear phagocyte population within the nodule and are intimately associated with the tissue necrosis which characterizes these lesions. Necrosis appears within small aggregates of mAb 5.5-positive cells. Similar cells are also associated with localized extensions of necrosis through the palisade zone. Centrifugal extension of the necrotic centers through incorporation of the inner cells of the palisade layer appears to be an independent phenomenon.