Identification and Expression of Human Cytomegalovirus Transcription Units Coding for Two Distinct Fcγ Receptor Homologs

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Abstract
Cellular receptors for the Fc domain of immunoglobulin G (IgG) (FcγRs) comprise a family of surface receptors on immune cells connecting humoral and cellular immune responses. Several herpesviruses induce FcγR activities in infected cells. Here we identify two distinct human cytomegalovirus (HCMV)-encoded vFcγR glycoproteins of 34 and 68 kDa. A panel of HCMV strains exhibited a slight molecular microheterogeneity between Fcγ-binding proteins, suggesting their viral origin. To locate the responsible genes within the HCMV genome, a large set of targeted HCMV deletion mutants was constructed. The mutant analysis allowed the identification of a splicedUL119-UL118mRNA to encode vFcγR gp68 andTRL11/IRL11to encode vFcγR gp34. Both vFcγRs are surface resident type I transmembrane glycoproteins. Significant relatedness of sequences in the extracellular chain of gpUL119-118 and gpTRL11 with particular immunoglobulin supergene family domains present in FcγR I and FcγRs II/III, respectively, indicates a different ancestry and function of gpUL119-118 and gpTRL11. The HCMV-encoded vFcγRs highlight an impressive diversification and redundancy of FcγR structures.