The CCL2/CCR2 axis in the pathogenesis of HIV-1 infection: a new cellular target for therapy?

The identification of chemokine receptors as necessary co-receptors for HIV entry into target cells represented a breakthrough in the understanding of the pathogenesis of this viral infection. Since this initial discovery, it was unraveled that chemokines, in addition to their role in blocking viral entry by binding to co-receptors, have other functions in HIV pathogenesis. Indeed, chemokines can either inhibit or enhance HIV replication, and these effects may involve both entry and post-entry events of the viral life cycle. Depending on the balance of their negative versus positive effects on HIV replication and spreading, chemokines contribute to different outcomes of HIV pathogenesis. CCL2 is unique among the chemokines in that mostly enhancing effects on viral replication and pathogenesis have been reported. Either HIV infection itself or exposure to viral products can induce the expression of this chemokine and of its receptor CCR2, and high levels of CCL2/CCR2 are indeed found in HIV-infected subjects. The CCL2/CCR2 axis is tightly linked to the high level of immune activation and inflammation that is the hallmark of HIV infection even in patients undergoing antiretroviral therapy. In addition, more direct effects of CCL2 on HIV replication are becoming apparent. Thus, modulation of CCL2/CCR2-driven effects may have significant impact on HIV disease progression. In this review, we will discuss the complex interaction between CCL2/CCR2 and HIV and the emerging therapeutic approaches based on the inhibition of this axis.