SUMMARY

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 t> IgG4> IgG2> 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. Infection with human cytomegalovirus (HCMV) induces th formation of Fc receptors for IgG in the host cell cytoplasm and cell surface (Frey & Einsfelder, 1984; Furukawa et al., 1975; Keller et al., 1976; Rahman et al., 1976; Westmoreland et al., 1976). Infection with herpes simplex virus (HSV) also induces Fc receptors on the infected cell surface (Watkins, 1964; Westmoreland & Watkins, 1974; Yasuda & Milgram, 1968), and their chemical nature