Fc receptor(s) induced by human cytomegalovirus bind differentially with human immunoglobulin G subclasses.

The IgG subclass specificity of Fc receptor(s) induced on cells by infection with human cytomegalovirus (HCMV) was studied in a binding assay by using infected cells and purified iodinated IgG of various subclasses from HCMV seronegative healthy adult donors. All four human IgG subclasses bound to HCMV-infected cells, with the following relative magnitudes: IgG1 greater than or equal to IgG4 greater than IgG2 greater than IgG3. The IgG subclass specificity of the Fc receptor was further analysed in an inhibition assay by using fragments prepared from purified human IgG by papain digestion, and using unlabelled subclass proteins. Fc but not Fab fragments inhibited the binding of 125I-labelled human IgG to HCMV-infected cells. The biological role of the Fc receptor in HCMV infection is discussed.