RANTES is a 7.8 kD member of the CC family of chemokines, also known as CCL5, which is expressed in T cells and monocytes/macrophages. RANTES is strongly chemotactic for monocytes/macrophages, memory T cells, eosinophils, and induces histamine release from basophils. In solution, RANTES can form high molecular weight aggregates that exhibit dissimilar biological activities to the dimeric form. Aggregates cause T cell and neutrophil activation while promoting HIV infection, whereas, the dimeric form exhibits RANTES-induced chemotaxis and inhibits HIV infection. Interestingly, as T cells become activated RANTES secretion appears to decrease.