CXCL4 belongs to a family of molecules called chemokines that help regulate the movement of immune cells around the body. In the mid-1990s, four chemokines—three discovered by Dr. Lusso, Robert Gallo, M.D., and their colleagues—were found in laboratory experiments to function as HIV inhibitors. These chemokines as well as CXCL4 may regulate the level of virus replication in infected individuals and thus the pace at which HIV disease progresses.
CXCL4 differs from the other four major HIV-suppressive chemokines in several respects. The other four chemokines inhibit HIV infection by binding to either one of two cell receptors—called CCR5 and CXCR4—used by the virus to attach to and enter immune cells, whereas CXCL4 binds directly to the outer surface of the virus. While the other chemokines bind to forms of HIV that use either the CCR5 or the CXCR4 receptor, CXCL4 can bind to and block infection by a wide variety of HIV strains, no matter what their receptor specificity. Finally, while the other chemokines are made primarily by immune cells, CXCL4 is made by platelets, the blood cells involved in clotting.