Figure 2.

Coreceptor usage determines viral entry into different cell types and uncovered the mystery of cellular tropism. Macrophages and primary T lymphocytes express CCR5 and CXCR4 where T cell lines express only CXCR4. Macrophage (M)-tropic HIV-1 strains infect macrophages and lymphocyte using CCR5, while T-cell line (T)-tropic strains infect lymphocytes and T cell lines (but not macrophages) by using CXCR4. All three cell types are infectable by the dual-tropic strains by using either coreceptors for entry. T lymphocytes are infectable by all strains of HIV.