Affiliations: Viral Evolution and Transmission Unit, Division of
Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific
Institute, Milan, Italy
Note: [] Corresponding author: Mariangela Cavarelli, PhD, Viral Evolution
and Transmission, San Raffaele Scientific Institute, Via Olgettina 58, 20132
Milano, Italy. Tel.: +39 022643 4907; Fax: +39 022643 4905; E-mail:
cavarelli.mariangela@hsr.it
Abstract: Human immunodeficiency virus type I (HIV-1) infects target cells
through interaction with the CD4 molecule and chemokine receptors, mainly CCR5
and CXCR4. Viral isolates can be phenotypically classified based on the
co-receptor they utilize to infect target cells. Thus, R5 and X4 virus use
respectively CCR5 and CXCR4, whereas R5X4 virus can use either CCR5 or CXCR4.
This review describes the central role played by co-receptor expression and
usage for HIV-1 cell tropism, transmission and pathogenesis. We discuss various
hypotheses proposed to explain the preferential transmission of R5 viruses and
the mechanisms driving the change of HIV-1 co-receptor usage in the course of
infection. Recent insights in the intrinsic variability of R5 viruses and their
role in influencing disease progression in both adults and children are also
discussed.
