Down-regulation of basophil function by human CD200 and human herpesvirus-8 CD200

Human and rodent CD200 are recognized by the inhibitory CD200R, and these molecules play an important role in the regulation of the immune system. Several viruses, such as human herpesvirus-6 (HHV-6), HHV-7, and HHV-8, possess a CD200 homologue, suggesting that these viruses regulate the immune response via CD200R. In this study, we analyzed the effect of human CD200 and the viral CD200 homologues on human CD200R-expressing cells. We found that human CD200R is predominantly expressed on basophils in amounts higher than on other human peripheral blood leukocytes. Furthermore, the viral CD200 homologues as well as human CD200 were recognized by human CD200R, and the activation of basophils was down-regulated by these CD200 proteins. These results suggested that CD200R is an important regulatory molecule of basophil activation. In addition, the presence of CD200 homologues on several viruses suggests a potentially unique relationship between basophil function and viral infection.