HIV can infect a variety of cells such as CD4+ helper T-cells and macrophages that express the CD4 molecule on their surface.
[2] The normal ligands for this receptor—RANTES, macrophage inflammatory protein (MIP)-1β and MIP-1α—are able to suppress HIV-1 infection in vitro.
T-tropic isolates, or syncitia-inducing (SI) strains replicate in primary CD4+ T-cells as well as in macrophages and use the alpha-chemokine receptor, CXCR4, for entry.
[1] The Trofile assay is a blood test that identifies the tropism of a patient's HIV.
The assay's purpose is to identify the tropism of an individual patient's HIV strain – R5, X4, or a combination of these known as dual/mixed (D/M).