Cytomegalovirus Strain AD169 Binds beta2 Microglobulin in Vitro after Release from Cells

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Abstract
Summary We previously reported that a host protein, β2 microglobulin (β2m) inhibited the detection of human cytomegalovirus (CMV) in urine specimens by enzyme immunoassay and postulated that β2m bound to the virus particle and masked the viral antigenic determinants. We report here that CMV strain AD169 grown in cell culture bound human β2m when this protein was added to cell culture fluids or when the virus was added to urine. Such binding was not seen with herpes simplex virus. CMV could also bind bovine β2m from foetal calf serum in cell culture fluids. The use of radiolabelled β2m in other experiments showed that CMV bound β2m after release from cells and that the bound β2m did not represent acquisition of class I HLA molecules during budding from host cell membranes. Immunoprecipitation studies showed that β2m was bound by two viral envelope proteins β2m BP1 (β2m-binding protein 1) and β2m BP2 of molecular masses 36000 and 65000 daltons respectively. β2m could not bind to separated viral proteins under reducing or non-reducing conditions. We propose that interaction of these two proteins on the viral surface is required to enable CMV to bind β2m.

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