Investigating neutrophil heterogeneity in infectious and inflammatory disease

Abstract

Neutrophils are the most abundant leukocyte in peripheral blood and there is growing interest in their roles in infectious and inflammatory disease. Recent studies have revealed that neutrophils may exhibit considerable emergent heterogeneity in response to diverse environmental cues, which may help to explain their differential functions in homeostasis and tissue inflammation. The first aim of this study was to assess changes in the production and phenotype of neutrophils in response to inflammatory challenge in mouse models. Next, we set out to extend these findings by performing an investigation of heterogeneity in human neutrophils from patients with two distinct inflammatory diseases, systemic lupus erythematosus (SLE) and coronavirus disease 2019 (COVID-19). Finally, an examination was carried out to determine the extent to which changes in neutrophil phenotype persisted during COVID-19 convalescence. Mice treated with a TRL3 ligand underwent haematopoietic remodelling that appeared to favour granulopoiesis, as well as a marked expansion of phenotypically immature neutrophils (based on low CD101 expression) in the bone marrow and circulation with enhanced capacity for production of the pro-inflammatory cytokine, TNF. Similar phenotypic changes were observed in lupus-prone mice. A comparison of the phenotype and function of peripheral blood neutrophils from patients and healthy controls revealed that neutrophils from SLE and COVID-19 patients displayed similar phenotypic alterations, such as increased expression of surface markers associated with activation (CD66b, CD64), reduced expression of maturity markers (CD10, CD101), as well as reduced expression of Fc and adhesion receptors (CD16 and CD62L). Furthermore, an expanded population of low-density neutrophils was found in both diseases. However, neutrophils from SLE patients displayed several alterations with potential immunomodulatory function, such as enhanced PD-L1 expression and increased capacity for production of B cell activating factor. In contrast, neutrophils from COVID-19 patients displayed a more activated phenotype that was severity dependent. Of particular significance was the observation that a number of neutrophil alterations, including impaired bacterial killing, persisted in convalescent COVID-19 patients for more than six months after initial hospitalisation with COVID-19. Taken together, these findings indicate that inflammatory challenge results in profound changes in neutrophil phenotype, some of which are disease specific. Our findings also indicate that COVID-19 can have a long-lasting impact on neutrophil phenotype that persists beyond the initial infection and which may have important functional consequences in some convalescent individuals.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ian Bruce (Supervisor), John Reynolds (Supervisor) & John Grainger (Supervisor)