Forward genetic and cellular studies of immune regulation: the roles of Carma1, Interleukin-10 and Gimap5

Thesis

The differentiation and functional specialisation of CD4⁺ T cells into distinct subsets allows inflammatory responses to be targeted to diverse types of insults. One subset of CD4⁺ T cells, Foxp3⁺ regulatory T (T_reg) cells, acts to restrain excessive effector T cell responses and can develop in either the thymus or peripheral tissues. Here, a mouse with a germline point mutation in Carma1, an essential component of the signalling cascade linking the T cell receptor to NF-κB activation, is described. These mice were used to demonstrate a cell-intrinsic requirement for Carma1 in the development of thymic T_reg cells that could be bypassed in peripheral CD4+ T cells. Interestingly, Carma1-deficient T_reg cells accumulated both at the site of persistent viral infection and in the intestine of healthy mice, which harbours a high load of resident bacteria, suggesting that chronic inflammation can drive peripheral T_reg cell induction or accumulation. Subsequent work showed that T_reg cells in colon of healthy wild-type mice are unique in that they constitutively produce the immunosuppressive cytokine interleukin 10 (IL-10), whereas in the small intestine both Foxp3⁺ T_reg cells and Foxp3^- CD4⁺ T cells that resemble Tr1 cells produce IL-10. Production of IL-10 from both T cell subsets required the presence of intestinal bacteria, because IL-10 expression was abrogated by broad-spectrum antibiotic treatment. Additionally, IL-10 expression was enhanced in the colon and caecum upon colonization with Helicobacter hepaticus, a pathogen that can break tolerance of intestinal bacteria in Il10^-/- mice. Finally, the characterisation of a mouse homozygous for a germline point mutation in Gimap5 demonstrated that this gene was required for the survival of T, B and NK lymphocytes. Additionally, these mice exhibited spontaneous hepatic extramedullary haematopoiesis, with an abundance of Lin^-Sca-1⁺Thy-1^high innate lymphoid cells in the liver, and became colitic when infected by H. hepaticus. Adoptively transferred lymphocytes prevented disease in these mice, suggesting that regulatory lymphocytes need Gimap5 to survive and function. Collectively, these studies identify novel genetic and microbial factors involved in maintaining intestinal homeostasis.

Authors: Barnes, MJ

• Publication date: 2010
• DOI: 10.5287/ora-4r9bqezgg
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: immune regulation; inflammatory bowel disease; mutagenesis; T cells; Gimap5; Carma1; Interleukin 10; cytokines
• Subjects: Gastroenterology; Pathology; Genetics (medical sciences); Immunology; Biochemistry; Haematology; Genetics (life sciences)