UL33 and UL78 interact with and modulate the surface expressions of CCR5 and CXCR4 in THP-1 cells. (A-D) Detection of heteromers in THP-1 cells by co-IP. THP-1 cells were transfected with (A) Flag-UL33, (B) Flag-UL78-YFP, (C) HA-CCR5 with or without Flag-UL33, or (D) HA-CCR5 with or without Flag-UL78-YFP. Lysates were immunoprecipitated with mouse anti-CXCR4 or rat anti-HA, resolved by SDS-PAGE and immunoblotted with the indicated antibodies. (E-H) Flow cytometry analysis of cell-surface (E-G) and total (F-H) CCR5 (E-F) or CXCR4 (G-H) expression using 1/85a Alexa Fluor 647–conjugated anti–human CCR5 (E-F) or PE-conjugated anti–human CXCR4 (G-H) in mock, Flag-UL33-YFP or Flag-UL78-YFP expressing THP-1 cells. The proportion of surface versus total receptors was calculated by comparing signals from nonpermeabilized and permeabilized cells in 3 independent experiments. Mock = pcDNA3 expression vector. Statistical differences compared with mock nucleofected cells were assessed using the Student t test (*P < .05; **P < .01; ***P < .001).