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At least three biochemically distinct Fcγ receptor classes have been described on human cells. These receptors have been designated FcγRI, FcγRII and FcγRIII. They are membrane glycoproteins with extracellular domains that contain immunoglobulin-like regions. Therefore, they are members of the immunoglobulin gene superfamily. They appear to be located on human chromosome 1 and may have arisen from gene duplication. All three Fcγ receptors are present on the surface of human macrophages.

Abnormalities of the thymus have long been noted in patients with myasthenia gravis (MG).1,2,3 Morphologically, the presence of germinal centers in the medulla of the MG thymus was described by Castleman in 1949.1 Functionally, the MG thymus cells have altered immunologic activity.2,3 Recently the development of monoclonal antibodies to T cell subsets allows for the furthur investigation of the MG thymus.4 We have used such monoclonal antibodies to investigate the MG thymus in tissue sections. We have compared these results to findings obtained in studies of suspended cells from the same thymus specimens.