M-Tropic Virus, Macrophage-Tropic Virus
A strain of HIV that enters and infects a host CD4 cell by attaching to the CCR5 coreceptor on the CD4 cell. To enter a CD4 cell, HIV must first attach to a CD4 receptor, then attach to either the CCR5 or CXCR4 coreceptor, and finally fuse its membrane with the CD4 cell membrane. HIV is usually R5-tropic (uses CCR5) during the early stages of infection, but the virus may later switch to using either only CXCR4 (X4-tropic) or both CCR5 and CXCR4 (dual-tropic). An HIV drug called a CCR5 inhibitor blocks HIV from attaching to the CCR5 coreceptor, which prevents HIV entry into the CD4 cell.