Extended Data Figure 4: Induction of type-I interferon is not required to trigger a death response in HIV-infected lymphoid CD4 T cells.

HIV-1 infections induce type-I interferon in vitro and in vivo⁶¹. To test the involvement of this antiviral response in modulating CD4 T-cell death, isolated CD4 T cells were infected with HIV-1 in the presence of neutralizing antibodies against the human interferon alpha receptor (IFNAR2), which blocks biological action of type I interferons. To determine the state of interferon signalling, cells were analysed in parallel for the presence of tyrosine-phosphorylated STAT1, which plays a central role in mediating type-I IFN-dependent biological responses, including induction of an antiviral state⁶². Phosphorylated STAT1 readily appeared in HIV-infected CD4 T cells, but not in HIV-infected cells treated with efavirenz (100 nM), AMD3100 (250 nM) or anti-IFNAR2 neutralizing antibodies (1–5 μg ml⁻¹). Notably, blocking interferon signalling with anti-IFNAR2 neutralizing antibodies did not prevent the death of CD4 T cells by HIV-1, although tyrosine phosphorylation of STAT1 was inhibited indicating effectiveness of the antibody blockade. The data suggest that this antiviral IFN induction is not critical to the onset of the innate immune death response leading to caspase 1 activation and pyroptosis. Error bars represent s.e.m. from three independent experiments using tonsil cells from three different donors.