Granulocyte-macrophage colony stimulating factor blockade promotes ccr9 ⁺ lymphocyte expansion in Nod2 deficient mice

Background: Ileal involvement in Crohn's disease (CD) is associated with NOD2 mutations and granulocyte-macrophage colony stimulating factor autoantibodies (GM-CSF Ab), and GM-CSF blockade promotes ileitis in Nod2/Card15-deficient (C15KO) mice. RALDH2-expressing dendritic cells (DC) and IL-4 promote CCR9 imprinting and small bowel homing of T lymphocytes, in conjunction with CCL25 expression by ileal epithelial cells (IEC). We hypothesized that GM-CSF neutralization promotes ileal disease by modulating expression of CCL25 by IEC and CCR9 by T lymphocytes via Nod2-dependent and independent pathways. Methods: CCL25 and CCR9 expression were determined in pediatric CD patients stratified by GM-CSF Ab. Ileitis was induced in C15KO mice via GM-CSF Ab administration followed by nonsteroidal antiinflammatory drug (NSAID) exposure, and expression of CCL25, CCR9, FOXP3, intracellular cytokines, and RALDH2 was determined in IEC and immune cell populations. Results: The frequency of CCL25 ⁺ IEC and CCR9 ⁺ T lymphocytes was increased in CD patients with elevated GM-CSF Ab. In the murine model, GM-CSF blockade alone induced IEC CCL25 expression, and reduced the frequency of mesenteric lymph node (MLN) CD4 ⁺FOXP3 ⁺ cells, while Card15 deficiency alone enhanced MLN DC RALDH2 expression. Both GM-CSF neutralization and Card15 deficiency were required for downregulation of MLN DC IL-10 expression; under these conditions NSAID exposure led to an expansion of IL-4 ⁺ and IL-17 ⁺ CCR9 ⁺ lymphocytes in the ileum. Conclusions: GM-CSF prevents ileal expansion of CCR9 ⁺ lymphocytes via Nod2-dependent and independent pathways. CCR9 blockade may be beneficial in CD patients with elevated GM-CSF Ab.