MCL1 and infection: Further characterization of proteins involved in the intrinsic apoptotic pathway showed no differences in the levels of pro-apoptotic BID or anti-apoptotic MCL-1 between WT and C8/R3-/- animals upon infection but did reveal increased levels of anti-apoptotic BCL-XL in mock control C8/R3-/- mice, and this was slightly diminished upon infection with SARS-CoV-2 (Fig. S3c).