Differential Functional Responses of Neutrophil Subsets in Severe COVID-19 Patients

Abstract

Neutrophils play a significant role in determining disease severity following SARS-CoV-2 infection. Gene and protein expression defines several neutrophil clusters in COVID-19, including the emergence of low density neutrophils (LDN) that are associated with severe disease. The functional capabilities of these neutrophil clusters and correlation with gene and protein expression are unknown. To define host defense and immunosuppressive functions of normal density neutrophils (NDN) and LDN from COVID-19 patients, we recruited 64 patients with severe COVID-19 and 26 healthy donors (HD). Phagocytosis, respiratory burst activity, degranulation, neutrophil extracellular trap (NET) formation, and T-cell suppression in those neutrophil subsets were measured. NDN from severe/critical COVID-19 patients showed evidence of priming with enhanced phagocytosis, respiratory burst activity, and degranulation of secretory vesicles and gelatinase and specific granules, while NET formation was similar to HD NDN. COVID LDN response was impaired except for enhanced NET formation. A subset of COVID LDN with intermediate CD16 expression (CD16Int LDN) promoted T cell proliferation to a level similar to HD NDN, while COVID NDN and the CD16Hi LDN failed to stimulate T-cell activation. All 3 COVID-19 neutrophil populations suppressed stimulation of IFN-γ production, compared to HD NDN. We conclude that NDN and LDN from COVID-19 patients possess complementary functional capabilities that may act cooperatively to determine disease severity. We predict that global neutrophil responses that induce COVID-19 ARDS will vary depending on the proportion of neutrophil subsets.

Obesity is associated with a distinct innate immune phenotype in severe COVID-19 patients

“…Moreover, the frequency of CD16+CD182+TREM-1+ HD neutrophils may also be affecting HLA-DR expression in monocytes of the obese group. Taken together, these outcomes suggest a strong association among peripheral innate cells and an alteration towards a sustained in ammatory response in patients with obesity, not seen in the non-obese group, which was already reported in previous studies during COVID-19 treatment 13,25,28,35 . Therefore, patients with obesity need careful monitoring during SARS-CoV-2 treatment.…”

“…Finally, red blood cell parameters were strongly associated with both LD and HD neutrophils expressing PD-L1 in patients with obesity. Consistently, there is a higher risk for endothelial damage and related complications in this population 37 , and neutrophils are suggested to be involved in coagulation and phagocytosis of red blood cells in COVID-19 35,38 . As we were not able to analyze endothelial functions, LD and HD neutrophils should be further explored in future studies, especially in populations with higher cardiovascular risk than individuals with obesity.…”

“…Neutrophil activity may also coordinate in ammatory signaling in patients with obesity as observed by the association between CD16 (FcγRIII) of mature HD neutrophils and IL-6 levels and a hyperactivated phenotype (CD16+CD182+TREM-1+) highly frequent among total leukocytes. One previous study including patients with obesity has shown that HD neutrophils became hyperactivated with enhanced phagocytosis, respiratory oxidative burst, degranulation, and neutrophil extracellular (NET) formation in COVID-19 severe patients 35 . TREM-1 is a triggering receptor expressed on myeloid cell type 1 able to amplify in ammatory responses and its soluble form (sTREM-1) is a biomarker of severity and mortality in COVID-19 36 .…”

“…Moreover, this increase of NK cells in our population with obesity was strongly and positively associated with the N/L ratio. An increase in this severity biomarker indicates a higher in ammatory response and it is implicated not only in infection diseases 35 , but obesity-associated features may also affect the N/L ratio 21 . In COVID-19, NK cells function, measured by the expression of granzymes and perforins was in uenced by higher levels of IL-6 33,34 .…”

Locally organised and activated Fth1hi neutrophils aggravate inflammation of acute lung injury in an IL-10-dependent manner

“…During the global pandemic of coronavirus disease 2019 (COVID- 19), researchers identified the emergence of a low-density neutrophil population expressing intermediate levels of CD16 from the peripheral blood and bronchial lavage fluid (BALF) of COVID-19-associated ARDS patients 8,9 . Such type of neutrophils demonstrated enhanced phagocytosis, neutrophil extracellular trap (NET) formation, platelet activation, cytokine production, T-cell activation, and impaired degranulation 10,11 , thus were considered as a predictor of risk for worse outcomes for COVID-19 patients. Furthermore, alveolar and circulating neutrophils in ARDS patients show delayed apoptosis as well as dramatic transcriptional profile alterations that confer resistance to phosphoinositide 3-kinase inhibition 12 .…”