Inflammatory Bowel Disease Basic

Introduction: The aetiology of Crohn's disease remains unclear, but it is characterised by an exaggerated immune response to mucosal antigen in patients with a genetic predisposition. In the gut, the primary antigen presenting cells, the dendritic cells (DC) and macrophages, may promote either a tolerogenic or an inflammatory T-cell response in response to mucosal antigen and are key to the primary pathophysiology of Crohn's disease. Here, we characterise DC and peripheral blood monocytes (macrophage precursors) in patients with Crohn's disease for identification, activation, homing markers and ongoing cytokine production. Methods: Peripheral blood mononuclear cells were isolated from adults with active luminal Crohn's disease and from healthy controls (HC). Multicolour flow cytometry was performed to assess DC subgroups: myeloid DC (mDC) and plasmacytoid DC (pDC). Additionally, monocytes were identified, and a subgroup analysis was made for comparison with the DC population. Expression of phenotypic markers (including maturation markers, homing markers and pattern recognition receptors) and assessment of on-going cytokine production (including TNFα, IL-6, IL-10) were assessed by intracellular staining. Results and Discussion: In patients with Crohn's disease, DC and monocytes expressed a stronger gut homing profile (CLA β7), whilst cells from HC had greater non-tissue-specific homing (CLAβ7) (Fig. A, B). This suggests that these cells have a predilection for travel to the gut from peripheral blood in Crohn's compared with HC. In examining subgroups of DC, we found in both Crohn's and HC, mDC were gut homing whilst pDC were strongly skin and lymph node homing, suggesting that they may have different roles in Crohn's, with mDC being central to gut inflammation, whilst pDC may be more involved in skin manifestations of disease. Production of pro-inflammatory cytokines was upregulated in Crohn's, with mDC producing high levels of TNFα (Fig. C) and pDC producing high levels of IL-6 (Fig. D), allowing these cells to direct a TH1 and TH17 immune response. The maturity marker CD86, indicating differentiation and ability to present antigen to T cells, was upregulated in mDC compared with pDC in Crohn's disease but not in HC. Additionally, the identified macrophage subgroup showed marked activation with elevated intracellular cytokine production and activation and homing markers in Crohn's compared with HC. Conclusions: This study demonstrates significant differences in maturation and homing marker expression and ongoing pro-inflammatory cytokine production by DC and macrophages in Crohn's disease. There are clearly differences in the roles of different DC subtypes in Crohn's, providing insight into the pathogenesis of this condition. That these changes are seen in cells in the peripheral blood before contact with inflamed gut indicates essential differences between the antigen presenting cell compartment of patients with Crohn's and HC, likely as a result of genetic predisposition. Vitamin D regulates dendritic cell activity and trafficking in Crohn's disease P BHAT, P HENDY,* D REDDI, D BERNARDO, L DURANT, A NOBLE, NR ENGLISH, SC KNIGHT, AL HART* *St Mark's Hospital, and Imperial College, London, UK Hospital Universitario de la Princesa, Madrid, Spain Australian National University Medical School, Canberra, Australia