Targeted modulation of neutrophil activity: impact on intestinal immunopathology

The intestinal immune system encounters the challenge of remaining unresponsive to the commensal microflora and food antigens whilst being able to mount a rapid immune response upon facing pathogens. Four major components contribute to gut homeostasis, including the epithelium, immune cells, intestinal microbes, and dietary metabolites. The importance of a tight control of immune response is emphasized in the context of chronic auto-inflammatory bowel diseases (IBD), such as Crohn's disease (CD) and Ulcerative Colitis (UC), where an immune response against commensals becomes dis-regulated.

While much of investigation into IBD has been focused on the peak of immunopathology driven by specific innate immune cells, called monocytes, and adaptive immune cells, called T helper (Th) cells, the first defining events in initiation of intestinal inflammation received less attention. Particularly, the specific role of another type of innate immune cells, called neutrophils, during colitis has not been clearly delineated. Neutrophils rapidly traverse the vascular endothelium to reach the intestinal lamina propria. Their presence in human colonic biopsies is considered to be a sign of active disease and is increasingly used as a secondary endpoint in clinical trials in UC. In both peripheral blood and mucosal tissue of IBD patients, they display altered phenotype and effector functions. Neutrophil activation was also reported to affect T cell populations, specifically influencing pathogenic Th cells. However, the extent of neutrophil contributions into the initiation and propagation of pathological intestinal inflammation, their interactions with other immune cells and immune-imprinting left on the tissue, remain largely unexplored.

Our recent findings demonstrate that, despite limited residence times in tissues, neutrophils can tailor their properties to mount specific and intrinsically regulated inflammatory response. Moreover, we have identified key molecular regulators specifically controlling neutrophil maturation or effector functions. This project will examine the functional impact of controlled modulation of neutrophil activity on the immunopathology of intestinal inflammation using the recently generated unique tools, such as genetically modified in vitro and in vivo models, newly discovered chemical inhibitors etc, and cutting-edge imaging and single cell genomic approaches. This may lead to the development of a new class of therapeutic strategies, based on selective modulation of neutrophil biology, to combat pathological inflammation and associated inflammatory disorders, such as IBD.

Neutrophils have been long considered as transcriptionally inactive cells, rapidly mobilised and degranulating in response to microbial insults. Our recent findings, and the developments in the field, have firmly established neutrophils as transcriptionally active cells that can tailor their properties to mount tissue specific and transcriptionally regulated inflammatory response and to support organ homeostasis. However, their molecular contribution in individual immunopathology, e.g. in ulcerative colitis (UC) where they are considered to be a sign of an active disease, has not been clearly delineated.

Our pilot data indicate that neutrophils are preferentially recruited to the mid and distal colon at the onset of Helicobacter hepaticus (+anti-IL-10R antibodies) driven mouse model of colitis, which are characterised by the elevated inflammation score. They also show that a neutrophil-specific knock-out of IRF5, one of the regulators of neutrophil effector functions identified by us, reduces immunopathology in this model. Building on these observations, we will first use cutting-edge single cell genomic approaches and advanced imaging to examine whether the site-specific neutrophil infiltration controls pathogenic monocyte recruitment and uncover neutrophil mediators involved. Next, we will investigate the mechanisms behind the reduced intestinal immunopathology observed under modulation of neutrophil activation, i.e. by neutrophil-specific ablation of IRF5. Finally, we will assess the therapeutic potential of a chemical inhibitor defactinib, shown by us to target the IRF5 signalling pathway, to block IRF5 activation in neutrophils, using both mouse colitis models and human pinch biopsies from the colonic mucosa of UC patients.

Overall, the proposed project will extend our understanding of the fundamental role neutrophils play at the onset of intestinal immunopathology, identify the regulators involved and map putative therapeutic strategies.