CCR5 and infection: While RANTES has been shown to act as a costimulator of T cells [47], [48], CCR5−/− T cells responded similarly to WT CD8 T cells in a competitive environment suggesting that the importance of RANTES during LCMV clone 13 infection was not due to direct costimulation of CD8 T cells, though other receptors capable of binding RANTES could have a role.