Ex vivo IL-1β, IL-6, TNF-α, and IL-8 responses 2 years after critical COVID-19 are associated with age and innate immune activation

Abstract A cytokine storm drives critical COVID-19, yet the determinants and long-term consequences of this exaggerated inflammatory response remain unclear. We investigated whether cytokine responsiveness remains altered 2 years after recovery from critical disease. In a cohort of 117 individuals with mild, severe, or critical COVID-19, acute-phase clinical and laboratory parameters were analyzed in moderate–severe and critical cases. Long-term immune function was assessed by ex vivo stimulation of whole blood with PMA/ionomycin, lipopolysaccharide (LPS), and phytohemagglutinin (PHA), followed by cytokine quantification and correlation with clinical parameters. A biobank of 76 patient-derived lymphoblastoid cell lines (LCL cells) was established to evaluate the stability of cytokine responses. During acute illness, critically ill patients exhibited marked inflammatory dysregulation, including lymphopenia (72%), neutrophilia (51%), elevated neutrophil-to-lymphocyte ratios, and increased C-reactive protein (median 91 mg/L) and ferritin (median 1,153 μg/L), consistent with a hyperinflammatory–hypercoagulable phenotype. Two years post-infection, individuals with prior critical disease showed more than threefold higher secretion of IL-1β, IL-6, TNF-α, and IL-8 following PMA/ionomycin (p < 0.0001) and LPS stimulation (p < 0.05) compared with younger mild cases, whereas PHA-induced responses remained comparable. PBMC counts were also higher in the moderate–severe and critical groups 2 years post-infection (p < 0.001), highlighting differences in cellular composition. LCL cells from critically ill donors secreted 79% more IL-8 and TNF-α than those from mild cases (p < 0.05). Collectively, these findings indicate differences in cytokine responsiveness 2 years after COVID-19 which correspond to prior disease severity and are associated particularly with age and innate immune activation.