PrCBL-23 but not CBL-23 is restricted for infection on HeLa/CD4 cells, HOS/CD4/CXCR4 cells and primary macrophages. (A) The infectious titer of prCBL-23 (solid bars) compared to TCLA CBL-23 (shaded bars) is shown for HeLa/CD4, HOS/CD4/CXCR4, and U87/CD4/CXCR4 cells. Virus-infected cells were fixed, and stained, and foci of infection were counted and calculated. CBL-23 can efficiently infect all three cell lines tested, whereas infection of HeLa/CD4 and HOS/CD4/CXCR4 cells is restricted for prCBL-23, even though it can efficiently infect U87/CD4/CXCR4 cells. (B) Comparative time course of infection by prCBL-23 (dotted line) and CBL-23 (solid line) on the T-cell line C8166, primary PBMCs, and primary macrophages. Equal quantities of infectious units (100 FFU, estimated on U87/CD4/CXCR4 cells) of both viruses were inoculated into cells, and the release of infectious virus was measured by RT activity and expressed as picograms per milliliter. The kinetics of infection shows that prCBL-23 can efficiently infect both C8166 cells and PBMCs but not macrophages. The kinetics of infection on PBMCs is, however, delayed (2 to 3 days) for prCBL-23 compared to CBL-23.