Expression and utilization of co-receptors in HIV and simian immunodeficiency virus infection of megakaryocytes

Objective: To analyse the expression and specificity of co-receptors for the entry of HIV and simian immunodeficiency virus (SIV) into megakaryocytes. Design and methods: The expression of co-receptors was determined by flow cytometric analysis in combination with reverse transcription-polymerase chain (RT-PCR) reaction. The specificity of co-receptors in virus entry was determined by the infection of HIV-1 pseudotyped with X4- (HXB2), R5- (YU2), or R5X4-tropic (89.6) envelope proteins of HIV-1 or with envelope proteins of SIVpbj1.9. Results: The model human erythroleukemia (HEL) cell line, exhibiting megakaryocytic-like properties, expressed CCR5, CCR3, CXCR4, and GPR15/BOB, and all viruses except YU2 (R5) efficiently entered the cells. The blocking of virus entry with specific chemokines showed that the entry of HXB2 (X4) was impaired by SDF-1β but not by other chemokines, indicating that CXCR4 was a major co-receptor for the entry of HXB2. Primary human bone marrow megakaryocytes displayed a different repertoire of co-receptor expression from that of HEL cells, as all viruses except YU2 efficiently entered these cells. However, chemokine blocking experiments showed that the entry of HXB2 into primary bone marrow megakaryocytes was insufficiently blocked by SDF-1β compared with the entry into HEL cells, suggesting that alternative co-receptors could be employed for the entry of X4 virus into bone marrow cells. Conclusion: These data suggest that cells of megakaryocytic lineage are susceptible to infection by X4 viruses, with less marked susceptibility to R5 isolates, and that SDF-1β efficiently blocks the infection of HEL cells but not of primary bone marrow megakaryocytes. Our data reveal that novel co-receptors are probably utilized for the entry of X4 virus into megakaryocytes.