Cartoon depicting the fluorescence intensity fluctuation traces coming from two different channels (CD4 and co-receptors), that is, homotypic interactions. The amplitude of the fluorescence fluctuation is related to the oligomeric state of the proteins under study. The cross-variance analysis renders information about heterotypic interactions. If heterotypic interactions are detected, colocalization analysis between these regions and HIV-1 virions is performed. Subsequently, the oligomeric state for these regions is extracted, obtaining the time-resolved oligomeric state of the interaction upon addition of the HIV-1 virions on the surface of live cells.