HIV-1 infection and chemokine receptor modulation.

In addition to the CD4 molecule that binds to the human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein gp120, productive HIV-1 infection requires interaction with cellular receptors for alpha- or beta- chemokines (CXCR4 and CCR5 respectively). Isolates of HIV-1 exhibit different tropism depending on the chemokine receptor type that they use to infect their cellular targets. HIV-1 strains that use preferentially CCR5 are known as R5 strains. They are more frequently found in asymptomatic individuals during the initial stages of the disease and are involved in the transmision of infection from mother to child. HIV-1 species using CXCR4 (X4 strains) are observed mainly in patients with advanced disease. While X4 isolates are associated with syncitium formation, in general R5 strains are not. Interaction of X4 and R5 with their specific receptors is necessary to establish productive HIV-1 infection and trigger a series of intracellular signals. Modulation of CXCR4 and CCR5 expression after HIV-1 infection is one of the results of such interaction and may have important consequences on the course of the infection. Down regulation of CCR5 and CXCR4 after HIV-1 infection could be the result of indirect events linked to HIV-1 infection, such as the induction of alpha- or beta-chemokines competing with the virions for receptor binding. They could also reflect direct effects of HIV-1 on chemokine-receptor turnover. In this review, the mechanisms of modulation of CXCR4 and CCR5 expression after HIV-1 infection will be discussed.