A viral CD200 homologue (vCD200) encoded by open reading frame R15 of rhesus rhadinovirus (RRV), a gammaherpesvirus closely related to human herpesvirus 8 (HHV-8), is described here. RRV vCD200 shares 30% and 28% amino acid identity with human CD200 (huCD200) and HHV-8 vCD200, respectively. In vitro analysis indicated that an Fc fusion (vCD200-Fc) is expressed as a glycoprotein with a core molecular mass of 53 kDa. Utilizing monoclonal antibodies raised against vCD200-Fc, vCD200 expression was detected on the surfaces of and within supernatants from infected fibroblasts. Furthermore, in vitro assays demonstrated that vCD200-Fc treatment of monocyte-derived macrophages reduces tumor necrosis factor transcript and protein levels, implying that RRV encodes a functional vCD200.