Dysregulated Neutrophil Phenotype and Function in Hospitalised Non-ICU COVID-19 Pneumonia

Abstract

Rationale: Infection with the SARS-CoV2 virus is associated with elevated neutrophil counts. Evidence of neutrophil dysfunction in COVID-19 is based on transcriptomics or single functional assays. Cell functions are interwoven pathways, and understanding the effect across the spectrum of neutrophil function may identify therapeutic targets. Objectives: Examine neutrophil phenotype and function in 41 hospitalised, non-ICU COVID-19 patients versus 23 age-matched controls (AMC) and 26 community acquired pneumonia patients (CAP). Methods: Isolated neutrophils underwent ex vivo analyses for migration, bacterial phagocytosis, ROS generation, NETosis and receptor expression. Circulating DNAse 1 activity, levels of cfDNA, MPO, VEGF, IL-6 and sTNFRI were measured and correlated to clinical outcome. Serial sampling on day three to five post hospitalization were also measured. The effect of ex vivo PI3K inhibition was measured in a further cohort of 18 COVID-19 patients. Results: Compared to AMC and CAP, COVID-19 neutrophils demonstrated elevated transmigration (p = 0.0397) and NETosis (p = 0.0332), and impaired phagocytosis (p = 0.0036) associated with impaired ROS generation (p < 0.0001). The percentage of CD54+ neutrophils (p < 0.001) was significantly increased, while surface expression of CD11b (p = 0.0014) and PD-L1 (p = 0.006) were significantly decreased in COVID-19. COVID-19 and CAP patients showed increased systemic markers of NETosis including increased cfDNA (p = 0.0396) and impaired DNAse activity (p < 0.0.001). The ex vivo inhibition of PI3K γ and δ reduced NET release by COVID-19 neutrophils (p = 0.0129). Conclusions: COVID-19 is associated with neutrophil dysfunction across all main effector functions, with altered phenotype, elevated migration and NETosis, and impaired antimicrobial responses. These changes highlight that targeting neutrophil function may help modulate COVID-19 severity.

Neutrophils are gatekeepers of mucosal immunity

“…However, some groups have disagreed with this view, demonstrating enhanced activation of immature neutrophils. One group has noted that immature neutrophils produced increased level of extracellular reactive oxygen species in vitro 97 and a separate in vitro human study has demonstrated increased immature neutrophil migration through CXCL8 signaling, with a higher predisposition toward NETosis correlating with severe COVID‐19 disease 98 . Thus, the exact functional role of these immature neutrophils is yet to be clarified.…”

Hyperactive immature state and differential CXCR2 expression of neutrophils in severe COVID-19

“…Neutrophil-soluble mediators, such as elastase and calprotectin, accumulate in plasma of patients with severe disease ( 29 , 30 ). Furthermore, NETs are elevated in the plasma of severe patients and correlate with lung failure and immunothrombosis ( 25 , 31 , 32 , 33 Preprint ), whereas isolated neutrophils from COVID-19 patients display elevated rates of both ROS production ( 34 ) and NETosis ( 35 , 36 ). Several studies have also reported expansion of low-density ( 37 ) and immature (CD10 low ) neutrophils ( 30 , 38 , 39 Preprint , 40 ), whose role in disease remains unclear.…”

The development of anticyclic citrullinated peptide (anti‐CCP) antibody following severe COVID‐19

“…The development of AAVs following COVID‐19 infection has been documented in the previous investigation 28 . Dysregulated neutrophil activation in hospitalized COVID‐19 patients may underpin the pathological processes involved in antineutrophil antibody development in COVID‐19 patients 29 …”

“…28 Dysregulated neutrophil activation in hospitalized COVID-19 patients may underpin the pathological processes involved in antineutrophil antibody development in COVID-19 patients. 29 In the study conducted by Zuo et al, it was found that higher titers of aPL antibodies are associated with neutrophil hyperactivity, comprising the release of neutrophil extracellular traps (NETs), higher platelet counts, more severe respiratory illness, and lower clinical estimated glomerular filtration rate. In contrast to this study that reported a significant occurrence of aPL antibodies in critically ill patients with COVID-19, 11 we have just detected IgG aPL autoantibodies in two critically infected COVID-19 patients.…”