SUMMARYThe 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.
Human cytomegalovirus-infected cell polypeptides were immunoreacted by sera of renal transplant recipients and compared with those reactive with sera of healthy adult donors by means of the Western immunoblotting technique. At least 15 polypeptides with molecular weights of 155K, 123K, 102K, 89K, 79K, 71K, 65K, 60K, 55K, 50K, 46K, 42K, 38K, 33K, and 28K were immunoreacted. Sera obtained serially from renal transplant recipients reacted with most of these polypeptides and reacted more frequently and intensely with the smaller polypeptide species such as 38K, 33K, and 28K, compared with sera of healthy seropositive adults. The implications of these findings are discussed.
Immunofluorescence assay using monospecific and monoclonal antibodies to the 65 K major protein of human cytomegalovirus (HCMV) was carried out to monitor the expression of this protein in infected cells. Regardless of differences in the reactivity of the monoclonal antibodies, as determined by immunoblotting and immunofluorescent staining, all stained cytoplasmic inclusion bodies localized to the site of the HCMV-induced receptor for the Fc portion of IgG, suggesting that most of the 65 K major protein of HCMV colocalizes with the HCMV-induced FcR.
The presence of HCMV-infected cells inhibits the killing of mouse tumor cells by adherent PEC in an antibody-dependent cell-mediated cytotoxicity (ADCC) test system. The effect of HCMV-infected cells on ADCC is mediated by the binding of IgG to the Fc receptors of infected cells.
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