Enhanced eosinophil-mediated inflammation associated with antibody and complement-dependent pneumonic insults in critical COVID-19

Abstract

Despite the worldwide effect of the Coronavirus disease 2019 (COVID-19) pandemic, the underlying mechanisms of fatal viral pneumonia remain elusive. Here, we show that critical COVID-19 is associated with enhanced eosinophil-mediated inflammation when compared to non-critical cases. In addition, we confirm increased Th2-biased adaptive immune responses, accompanying overt complement activation, in the critical group. Moreover, enhanced antibody responses and complement activation is associated with disease pathogenesis as evidenced by formation of immune complexes and membrane attack complexes in airways and vasculature of lung biopsies from six fatal cases, as well as by enhanced hallmark gene set signatures of FcγR signaling and complement activation in myeloid cells of respiratory specimens from critical COVID-19 patients. These results suggest that SARS-CoV-2 infection may drive specific innate immune responses, including eosinophil-mediated inflammation, and subsequent pulmonary pathogenesis via enhanced Th2-biased immune responses, which might be crucial drivers of critical disease in COVID-19 patients.

A humanized ACE2 mouse model recapitulating age‐ and sex‐dependent immunopathogenesis of COVID‐19

“…There were marginal changes in the proportion of dendritic cells (DCs) in the lungs of infected mice, even though these innate immune cells slightly decreased in both of the infected mice groups. These observations are consistent with the altered pulmonary myeloid cell profiles seen in COVID‐19 patients, which differ according to the severity of the disease 9,22,23 …”

“…In this context, we were able to specifically demonstrate that eosinophil‐mediated inflammation may play a critical role in severe disease progression and increased mortality, depending on infection conditions and host gender. This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil‐mediated inflammation in severe COVID‐19 progression still needs to be defined 9 . Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long‐COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research 33…”

“…Furthermore, nine factors (CXCL10, CCL11, C5a, IFNA, ECP, EDN, CCL12, GCSF, and GDF15) were significantly more elevated in middle‐aged mice than in young mice. The enhanced expression of these factors was also reproducibly observed in COVID‐19 patients depending on the severity of their disease, 9,20 suggesting that our mouse model may effectively mimic the immunological pathogenesis of COVID‐19 in humans.…”

“…This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil-mediated inflammation in severe COVID-19 progression still needs to be defined. 9 Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long-COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research. 33 SARS-CoV-2 variants have multiple spike protein mutations that affect infectivity, transmissibility, and immune escape.…”

A humanized ACE2 mouse model recapitulating age‐ and sex‐dependent immunopathogenesis of COVID‐19

“…There were marginal changes in the proportion of dendritic cells (DCs) in the lungs of infected mice, even though these innate immune cells slightly decreased in both of the infected mice groups. These observations are consistent with the altered pulmonary myeloid cell profiles seen in COVID‐19 patients, which differ according to the severity of the disease 9,22,23 …”

“…In this context, we were able to specifically demonstrate that eosinophil‐mediated inflammation may play a critical role in severe disease progression and increased mortality, depending on infection conditions and host gender. This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil‐mediated inflammation in severe COVID‐19 progression still needs to be defined 9 . Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long‐COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research 33…”

“…Furthermore, nine factors (CXCL10, CCL11, C5a, IFNA, ECP, EDN, CCL12, GCSF, and GDF15) were significantly more elevated in middle‐aged mice than in young mice. The enhanced expression of these factors was also reproducibly observed in COVID‐19 patients depending on the severity of their disease, 9,20 suggesting that our mouse model may effectively mimic the immunological pathogenesis of COVID‐19 in humans.…”

“…This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil-mediated inflammation in severe COVID-19 progression still needs to be defined. 9 Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long-COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research. 33 SARS-CoV-2 variants have multiple spike protein mutations that affect infectivity, transmissibility, and immune escape.…”

Both COVID-19 infection and vaccination induce high-affinity cross-clade responses to SARS-CoV-2 variants

“…Our observation was corroborated by repeating the measurements using the same IgG4-specific secondary antibody as well as by using the same clone from an alternative source (including differences in concentrations and storage buffers), which makes us confident that the results presented are valid. Moreover, we presented one of the most comprehensive cross-validations to date of all secondary antibodies -widely used in research on SARS-CoV-2 (Crowley et al, 2021;Fraley et al, 2021;Kim et al, 2021;Lee et al, 2021;Newell et al, 2021;Phelan et al, 2021;Pullen et al, 2021;Yates et al, 2021) and in other fields (Minassian et al, 2021;Sanchez Vargas et al, 2021;Tschismarov et al, 2021;Jennewein et al, 2022;Toney et al, 2022) -employed in this study and have confirmed their specificity to their target. We have noted that the sensitivity of the anti-human IgG1 antibody used can benefit from a higher concentration; however, it would come at a cost of compromising its specificity as the antibody shows cross-reactivity to other IgG subtypes at slightly increased concentrations, therefore, presenting a less favorable sensitivity-to-specificity profile than the other secondary antibodies.…”

A humanized ACE2 mouse model recapitulating age‐ and sex‐dependent immunopathogenesis of COVID‐19

“…There were marginal changes in the proportion of dendritic cells (DCs) in the lungs of infected mice, even though these innate immune cells slightly decreased in both of the infected mice groups. These observations are consistent with the altered pulmonary myeloid cell profiles seen in COVID‐19 patients, which differ according to the severity of the disease 9,22,23 …”

“…In this context, we were able to specifically demonstrate that eosinophil‐mediated inflammation may play a critical role in severe disease progression and increased mortality, depending on infection conditions and host gender. This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil‐mediated inflammation in severe COVID‐19 progression still needs to be defined 9 . Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long‐COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research 33…”

“…Furthermore, nine factors (CXCL10, CCL11, C5a, IFNA, ECP, EDN, CCL12, GCSF, and GDF15) were significantly more elevated in middle‐aged mice than in young mice. The enhanced expression of these factors was also reproducibly observed in COVID‐19 patients depending on the severity of their disease, 9,20 suggesting that our mouse model may effectively mimic the immunological pathogenesis of COVID‐19 in humans.…”

“…This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil-mediated inflammation in severe COVID-19 progression still needs to be defined. 9 Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long-COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research. 33 SARS-CoV-2 variants have multiple spike protein mutations that affect infectivity, transmissibility, and immune escape.…”

Both COVID-19 infection and vaccination induce high-affinity cross-clade responses to SARS-CoV-2 variants

“…Our observation was corroborated by repeating the measurements using the same IgG4-specific secondary antibody as well as by using the same clone from an alternative source (including differences in concentrations and storage buffers), which makes us confident that the results presented are valid. Moreover, we presented one of the most comprehensive cross-validations to date of all secondary antibodies -widely used in research on SARS-CoV-2 (Crowley et al, 2021;Fraley et al, 2021;Kim et al, 2021;Lee et al, 2021;Newell et al, 2021;Phelan et al, 2021;Pullen et al, 2021;Yates et al, 2021) and in other fields (Minassian et al, 2021;Sanchez Vargas et al, 2021;Tschismarov et al, 2021;Jennewein et al, 2022;Toney et al, 2022) -employed in this study and have confirmed their specificity to their target. We have noted that the sensitivity of the anti-human IgG1 antibody used can benefit from a higher concentration; however, it would come at a cost of compromising its specificity as the antibody shows cross-reactivity to other IgG subtypes at slightly increased concentrations, therefore, presenting a less favorable sensitivity-to-specificity profile than the other secondary antibodies.…”

A humanized ACE2 mouse model recapitulating age‐ and sex‐dependent immunopathogenesis of COVID‐19

“…There were marginal changes in the proportion of dendritic cells (DCs) in the lungs of infected mice, even though these innate immune cells slightly decreased in both of the infected mice groups. These observations are consistent with the altered pulmonary myeloid cell profiles seen in COVID‐19 patients, which differ according to the severity of the disease 9,22,23 …”

“…In this context, we were able to specifically demonstrate that eosinophil‐mediated inflammation may play a critical role in severe disease progression and increased mortality, depending on infection conditions and host gender. This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil‐mediated inflammation in severe COVID‐19 progression still needs to be defined 9 . Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long‐COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research 33…”

“…Furthermore, nine factors (CXCL10, CCL11, C5a, IFNA, ECP, EDN, CCL12, GCSF, and GDF15) were significantly more elevated in middle‐aged mice than in young mice. The enhanced expression of these factors was also reproducibly observed in COVID‐19 patients depending on the severity of their disease, 9,20 suggesting that our mouse model may effectively mimic the immunological pathogenesis of COVID‐19 in humans.…”

“…This was confirmed by depleting the innate immune cell population but not by neutrophil depletion (Figure 6), even though a more detailed mechanism regarding the immunopathogenic role of eosinophil-mediated inflammation in severe COVID-19 progression still needs to be defined. 9 Furthermore, the genetic and functional stability of ACE2 in our model could guarantee the advancement of long-COVID phenotype modeling, showcasing various inflammatory sequelae in numerous organs related to the disease in subsequent research. 33 SARS-CoV-2 variants have multiple spike protein mutations that affect infectivity, transmissibility, and immune escape.…”

Both COVID-19 infection and vaccination induce high-affinity cross-clade responses to SARS-CoV-2 variants

“…Our observation was corroborated by repeating the measurements using the same IgG4-specific secondary antibody as well as by using the same clone from an alternative source (including differences in concentrations and storage buffers), which makes us confident that the results presented are valid. Moreover, we presented one of the most comprehensive cross-validations to date of all secondary antibodies -widely used in research on SARS-CoV-2 (Crowley et al, 2021;Fraley et al, 2021;Kim et al, 2021;Lee et al, 2021;Newell et al, 2021;Phelan et al, 2021;Pullen et al, 2021;Yates et al, 2021) and in other fields (Minassian et al, 2021;Sanchez Vargas et al, 2021;Tschismarov et al, 2021;Jennewein et al, 2022;Toney et al, 2022) -employed in this study and have confirmed their specificity to their target. We have noted that the sensitivity of the anti-human IgG1 antibody used can benefit from a higher concentration; however, it would come at a cost of compromising its specificity as the antibody shows cross-reactivity to other IgG subtypes at slightly increased concentrations, therefore, presenting a less favorable sensitivity-to-specificity profile than the other secondary antibodies.…”