CD4 and infection: The SERINC5 down-regulation activity of 106 Nef clones, isolated from patients in early infection and for which CD4 and HLA-I down-regulation activities [15] as well as alteration of TCR signalling activity [16] had previously been measured, was evaluated in a CEM-derived CD4 + T cell line using a flow cytometry-based assay and then related to subsequent rate of CD4 + T cell decline and viral load set point.