A group from Max Planck Institute of Immunobiology and Epigenetics, etc. has found that IL-33 expression in COVID-19 covalescent individuals correlates with seropositivity of SARS-CoV-2 specific IgG.
https://www.nature.com/articles/s41467-021-22449-w
Authors purified PBMCs from COVID-19 covalescent 20 individuals and examined their composition using conventional CD markers, and monitored cytokine production with activation following SARS-CoV-2 Spike stimulation. It was found that IL-33 was most strongly correlated with CD4+CD69+ T-cells among cytokines investigated here, IL-33, IL-6, IFN-ɑ2, and IL-23. IL-33 has a high homology amino acid sequence with IL-1β and IL-18 and belongs to the IL-1 family, but its detailed characteristics are still unknow. Authors have investigated the source of IL-33 in PBMCs by staining for intracellular IL-33 in conjunction with cell-specific markers, and found that it was most highly expressed in CD14+ monocytes. However, there were no differences in the frequency of IL-33+ cells in PBMC from seropositive vs. seronegative individuals, suggesting that the emergence of COVID-19-specific T cells that are capable of eliciting the release of bioactive IL-33 from other cells that constitutively produce this cytokine. These results suggest that IL-33 might be deeply linked to COVID-19 pathogenesis and immunity.
