Airway epithelial cells and macrophages trigger IL-6-CD95/CD95L axis and mediate initial immunopathology of COVID-19
Airway epithelial cells (AEC) are the first in contact with SARS-CoV-2 and drive the interface with macrophage to generate inflammation. To elucidate how those initial events contribute to the immunopathology or to dysregulate the immune response observed in severe and critical COVID-19, we determined the direct and indirect interactions of these cells. AEC lineage (Calu-3) infected with SARS-CoV-2 and epithelial cells (CD45-EpCAM+) from intubated COVID-19 patients showed high expression of CD95L. Infected-Calu-3 cells secreted IL-6, and expressed annexin V and caspase-3, apoptosis markers. The direct interaction of macrophages with sorted apoptotic Calu-3 cells, driven by SARS-CoV-2 infection, resulted in macrophage death and increased expression of CD95, CD95L and CD163. Macrophages exposed to tracheal aspirate supernatants from intubated COVID-19 patients or to recombinant human IL-6 exhibited decreased HLA-DR and increased CD95 and CD163 expression. IL-6 effects on macrophages were prevented by tocilizumab (anti-IL-6 receptor mAb) and Kp7-6 (CD95/CD95L antagonist). Similarly, lung inflammation and death of AEC were decreased in CD95 and IL-6 knockout mice infected with SARS-CoV-2. Our results show that the AEC-macrophage interaction via CD95/CD95L signaling is an initial key step of immunopathology of severe COVID-19 and should be considered as a therapeutic target. O_FIG O_LINKSMALLFIG WIDTH=181 HEIGHT=200 SRC="FIGDIR/small/504760v1_ufig1.gif" ALT="Figure 1"> View larger version (88K): org.highwire.dtl.DTLVardef@aadef5org.highwire.dtl.DTLVardef@13d033org.highwire.dtl.DTLVardef@c9c555org.highwire.dtl.DTLVardef@ba821e_HPS_FORMAT_FIGEXP M_FIG C_FIG Highlights- SARS-CoV-2-infected airway epithelial cells (AEC) secrete IL-6, express Fas/FasL and undergo apoptosis; - SARS-CoV-2-infected apoptotic AEC induces Fas/FasL expression and death in macrophages; - IL-6 induces IL-1{beta} secretion, reduction of HLA-DR and increase of Fas and CD163 expression in macrophages; - Blockade of IL-6 signaling and Fas/FasL restores the expression of HLA-DR and reduces the expression of Fas and CD163, and secretion of IL-1{beta} on isolated macrophages; in vivo, the deficiency of Fas and IL-6 decreases acute pulmonary inflammation in SARS-CoV-2-infected mice.