Background. Antigen presenting cells (APCs) are key regulators of immune responses in the gut. The aim of this project is to identify and investigate mechanisms by which these cells are able to keep peace in the intestine. Understanding of how gut APCs regulate immunity may be exploited to identify new targets for treatment of intestinal diseases and improve oral vaccine design for infections.
To maintain homeostasis in the gut, the local immune system must rapidly eliminate infectious pathogens to avoid life-threatening infections – and at the same time tolerate the normal microbiota and food antigens to avoid chronic inflammatory disorders. To accomplish this task, the innate part of the gut immune system is organized with a strategically positioned layer of APCs, including macrophages and dendritic cells (DCs), in close proximity to the surface epithelium.
APCs have several functions in defense against invading pathogens; they are specialized both for rapid elimination of pathogens, for alarming surrounding cells by secreting proinflammatory cytokines, and they function as APCs with a unique capacity to activate T cells. In addition, immune cells in the intestine have to distinguish between harmful pathogens and the large number of commensal microorganisms and food proteins normally occurring in the gut to avoid chronic inflammations – such as inflammatory bowel disease and unwanted reactions to foods (like celiac disease).
To exert these functions, APCs are equipped with a wide range of cell surface receptors (pattern recognition receptors, PRRs) that recognize conserved molecules expressed by pathogens (pathogen-associated molecular patterns, PAMPs). Recognition of PAMPs enhances their phagocytic capacity, increases their secretion of cytokines, and promotes their capacity to activate T cells.
Much of our understanding of how APC subsets regulate immunity is derived from experimental mice, where recent studies have shown that macrophages and DCs can be further classified into several subpopulations with very different functions, dependent of their origin and of the local microenvironment within which they operate. However, caution should be made to translate results from mice into humans, as recent reports have demonstrated that inflammatory responses in mice and humans can be very different.
Project: To understand how the human intestinal immune system works, human macrophage- and DC subsets will be studied directly in the tissue where they exert their function, both in the normal state and in celiac disease. To study such APCs, we have developed methods for purification and culture of cells from intestinal mucosal tissue, and the different APC-populations within such fractions are identified by multicolor flow cytometry in combination with immunofluorescence stainings of tissue sections.
Specific aim: To identify the cytokine production potential of human intestinal APCs.
APCs isolated from the gut will be incubated with different components or analogues of pathogens (PAMPs, bacterial and viral) together with combinations of inflammatory cytokines. Following brief incubations, the cytokines produced by the different APC-populations will be analyzed by flow cytometry using cytokine-specific antibodies together with markers defining the APC subsets. Supernatants containing soluble factors derived from intestinal APCs will also be added to T cell cultures to assess their stimulatory potential. To identify the factors activating T cells, blocking antibodies to cytokines will be applied during culture.
During the project, the candidate will acquire extensive experience in cell culture techniques, advanced flow cytometry and confocal microscopy.
This project is a joint effort between the Centre of Immune Regulation and several clinical departments at Oslo University Hospital, in close collaboration with international leading experts in immunology.