Caspase-1 up-regulation is not limited to the acute stage of COVID-19 disease
Up to 87% of inpatients and 35% of outpatients who recover from COVID-19 report persistence of at least 1 symptom, particularly fatigue and dyspnea (32, 33). Although preliminary reports describe this new feature as “post-COVID-19 syndrome”, its mechanisms and natural history remains unknown. We assayed caspase-1 activity in CD4+ T cells of health care workers (HCWs) with persistent respiratory and/or neurological (fatigue) symptoms at least 90 days post-SARS-CoV-2 infection (Table 2 ). There was statistically significant up-regulation of baseline as well as nigericin stimulated T-helper cell caspase-1 levels only in symptomatic “post-COVID-19” HCWs, also known as long haulers (Figure 3 ). An asymptomatic group of patients with history of PCR+ virus infection no flu like illness preceding the PCR test and absent seroconversion showed elevated T-helper cell caspase-1 expression. Interestingly, PCR-negative symptomatic HCWs with history of flu-like illness in early 2020 as well as those with positive IgG to SARS-CoV-2 also had increase caspase-1 expression. The level of expression of nigericin stimulated caspase-1 was comparable to those with active infection as seen in Figure 2, although the baseline caspase-1 levels are lower in long haulers. Non-exposed control subjects showed no T cell caspase-1 overexpression. The non-exposed subjects were identified from a different geographical area (Fairfax, Virginia, USA), at a time when the pandemic was at its lowest numbers (August-September 2020). These subjects were also exercising strict self-isolation.
Pan-caspase inhibitor suppresses elevated caspase-1 activity in CD4 + T cells derived from moderate-severe COVID-19 patients
To assess whether CD4+ T cell caspase-1 activity can be suppressed by small molecule caspase inhibitors, we incubated whole blood samples with either the oral pan-caspase inhibitor emricasan (EMR) (34) or the selective orally active ICE/caspase-1 inhibitor VX765 (35), followed 24hrs later with or without nigericin stimulation. We found that EMR suppressed CD4+ T cell caspase-1 activity in COVID-19 samples or prevented its upregulation in healthy subjects (Figure 4 ), while VX765 showed only minimal suppressive effect.