MCL1 and viral infectious disease: Myeloid Cell Leukemia-1 (MCL-1), a key regulator of mitochondrial apoptosis, is expressed as one anti-apoptotic isoform (MCL-1 L) and two pro-apoptotic isoforms (MCL-1 S and MCL-1ES), but their regulation in pediatric viral infections remains unclear.<h4>Methods and results</h4>We assessed MCL-1 isoform expression by RT-qPCR and circulating protein levels by ELISA in 324 unvaccinated children (179 SARS-CoV-2-positive and 145 SARS-CoV-2-negative), most with chronic conditions.