CD4 and HIV-1 infection: Considering that CD8+ T cells play a critical role in the immune response against HIV-1 infection during chronic infection (Gulzar and Copeland, 2004; Mudd and Lederman, 2014), we further attempted to identify specific ligand–receptor pairs between CD4+ T cells and cytotoxic T lymphocytes to characterize the immune response induced by HIV-1-infected cells (Gulzar and Copeland, 2004).