Fc gamma RII restriction fragment length polymorphism (RFLP): analysis in systemic lupus erythematosus and scleroderma and evidence of an alpha gene duplication.

The characteristic finding of high levels of circulating immune complexes in patients with the autoimmune connective tissue diseases systemic lupus erythematosus (SLE) or scleroderma has raised the possibility that these patients may have a primary defect in immune complex clearance. The Fc receptor for IgG (Fc gamma R) plays a central role in the phagocytosis of antibody complexes. We have analysed Fc gamma R (type II) RFLPs identified in TaqI- and MspI-restricted genomic DNA and found that their distribution in SLE and scleroderma did not differ significantly from controls. Hybridization with specific regions of the Fc gamma RII cDNA clone indicate that part of the Fc gamma RII alpha locus is duplicated in some individuals. A further Fc gamma RII gene has recently been identified (Fc gamma RII alpha'). This gene shows greater than 95% homology with Fc gamma RII alpha and may thus be the candidate gene for the apparent alpha duplication seen in some individuals. It is possible that an individual may possess one, two, three or four TaqI Fc gamma RII alpha/alpha' alleles, correlating with incidence and numerical heterogeneity in Fc gamma RII alpha and alpha'. The physiological effects of this numerical heterogeneity remain to be investigated.