The receptor through which M-tropic HIV strains bind -

HIV-1 most commonly uses the chemokine receptors CCR5 and/or CXCR4 as co-receptors to enter target immunological cells. Option 1: Macrophage (M-tropic) strains of HIV-1, or non-syncitia-inducing strains (NSI) use the beta-chemokine receptor CCR5 for entry and are thus able to replicate in macrophages and CD4+ T-cells. These strains are now called R5 viruses. Option 2: T-cell line (T-tropic) isolates or syncytium-inducing (SI) strains replicate in primary CD4+ T-cells as well as in macrophages and use the alpha-chemokine receptor, CXCR4, for entry. Option 3: CXCR5 in B-cell and tumor cell responses: expressed in Burkitt Lymphoma and Intraocular Lymphoma.