UNIDIRECTIONAL BUDDING OF HIV-1 AT THE SITE OF CELL-TO-CELL CONTACT IS ASSOCIATED WITH CO-POLARIZATION OF INTERCELLULAR-ADHESION MOLECULES AND HIV-1 VIRAL MATRIX PROTEIN

Objectives: To explore the possibility that HIV-1 budding and cellular adhesion molecules co-polarize at cell-to-cell contact sites. To inve stigate the incorporation of host-cell-derived adhesion molecules into HIV-1. Methods: The cellular sites involved in HIV-1 budding were exa mined by transmission electron microscopy. Single and double immunocyt ochemistry staining was used to evaluate the cellular distribution of the viral matrix protein and adhesion molecules. Quantitative flow cyt ometry was used to measure the cellular expression of adhesion molecul es. An immunocapture technique was used to measure the presence of cel l-derived proteins on HIV-1. The captured virus was measured by a p24 antigen assay. The infectivity of virus captured by monoclonal antibod ies was tested by measuring the virus antigen yield in supernatants af ter the addition of sensitive cells. Results: Released and budding HIV -1 was mainly localized at the cell-to-cell contact regions. This feat ure was consistent with a polarized staining for the virus matrix prot ein p18 at cell-to-cell contact regions. Intercellular adhesion molecu les (ICAM)-1 in HIV-1-infected cells were polarized on both isolated c ells and syncytia, co-localizing with HIV-1 matrix protein. HIV-1 inco rporated all the adhesion molecules expressed by the host cells, altho ugh without quantitative correlation with their cellular expression. C onclusions: HIV-1 is released at cell-to-cell membrane contact sites. Both ICAM-1 and virus matrix protein co-polarized on isolated cells an d syncytia at the sites involved in the recruitment of uninfected cell s. The impressive concentration of ICAM at cell sites where most virio ns are released may account for the acquisition of these membrane prot eins by the HIV-1 progeny, and may be important for the cell-mediated spread.