CD4 and infection: We demonstrate that unlike CD4+ T cells, which are rapidly depleted by HIV-1 infection and do not release IL-1β or IL-18 (Linder et al., 2020), primary macrophages release pro-inflammatory cytokines in response to HIVPR during cell-to-cell infection from infected primary CD4+ T cells and T cell lines (Figures 3 and 4), thus representing a potential source of sustained IL-1β and subsequent chronic immune activation.