<prompt> The receptor through which M - tropic HIV strains bind?CCR5CXR4CXCR5Any of the above  <response>: Ans. is a i.e., CCR5Ref: Chemokines in Disease, 4the, p. 136 Macrophage M - tropic strains of HIV - 1, or non - synctia 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. The normal ligands for this receptor, RANTES, macrophage inflammatory protein MIP - l - beta and MIP-1- alpha, are able to suppress HIV - 1 infection in vitro. This CCR5 coreceptor is used by almost all primary HIV - 1 isolates of viral genetic subtype. T - tropic isolates or synctia inducing SI strains replicate in primary CD4 T cells as well as in macrophages and use the alpha - chemokine receptor, CXCR4, for entry. 