Cytomegalovirus in Urine Specimens Has Host beta2 Microglobulin Bound to the Viral Envelope: A Mechanism of Evading the Host Immune Response?

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Abstract
Summary We have previously reported that human cytomegalovirus (CMV) from urine specimens cannot be captured onto a solid phase by CMV-specific monoclonal antibodies that can capture CMV grown in vitro. We report here that CMV exists in vivo in body fluids such as urine as β2 microglobulin (β2m)-coated particles. We have demonstrated the presence of β2m on CMV purified directly from urine by Western blotting and have shown that the β2m was associated with the viral envelope. Urinary CMV could be specifically bound by an affinity column comprising a monoclonal antibody specific for β2m bound to Sepharose. The β2m-coated urinary CMV could not be neutralized by hyperimmune globulin, human immune sera or murine monoclonal antibodies that could neutralize CMV grown in cell culture. We conclude that the binding of β2m by CMV masks the important antigenic sites necessary for neutralization which are recognized by man's immune response. We propose that CMV has evolved this mechanism of coating itself in a host protein as a mechanism of evading the host immune response and facilitating transmission between individuals.