Effect of UL33 and UL78 expression on CCR5 and CXCR4 ligand binding properties. Saturation isotherms of fluorescence labeled CCL3 (A) and CXCL12 (C) binding in HEK293 cells expressing Halo-Myc-CXCR4 (C, closed squares) or Halo-Myc-CCR5 (A, closed squares) receptors alone or with Flag-UL33-YFP (closed circles) or Flag-UL78-YFP (closed triangles). Specific binding is shown; nonspecific binding was determined in the presence of 1μM CXCL12 for CXCR4 and 10μM of Maraviroc for CCR5. (B-D) Flag-UL33-YFP or Flag-UL78-YFP expression was assessed using Lumi4-Tb labeled anti-Flag antibodies. Data shown are representative of 3 experiments. Statistical differences compared with mock nucleofected cells were assessed using the Student t test (*P < .05; ***P < .001).