Crohn's Disease: Current Pathogenetic Paradigms

Fluorescence microscopy and flow cytometric analysis of Peyer's patches and intestinal immune cells

In recent years researchers have become more aware of the importance of the gut-associated immune system since it is in direct interaction with the entry site for virus, bacteria, and all type of food contaminants, including numerous toxins that can alter mucosal immunity. Peyer's patches (PP) are considered the inductive site for protein antigen presentation in the gut as well as the starting point for IgA B-cell differentiation. The IgA found in feces comes from IgA secreted by IgA lamina propria lymphocytes (LPL), and its presence is a sign of normal physiology, in that IgA plays a role in absorption and immune defense against gut-associated pathogens. Methods presented in this unit are intended to analyze PP and intestinal intraepithelial and LPL to determine whether the complexity of the mucosal-associated lymphoid tissue and its components have been altered by any form of external damage. The protocols explain how to isolate and culture isolated cells; how to stain and analyze; and also how to cryopreserve the gut.

Impaired peripheral Th1 CD4+ T cell response to Escherichia coli proteins in patients with Crohn's disease and ankylosing spondylitis

BACKGROUND

To clarify the impact of T cell responses towards enteric antigens for chronic intestinal inflammation, we determined T helper 1 reactivity towards conserved Escherichia coli proteins in patients with Crohn's disease (CD) and healthy individuals and patients with ankylosing spondylitis (AS), who also often show microscopic inflammatory lesions within the gut or even develop overt inflammatory bowel disease.

METHODS

We determined the frequency of IFNγ+CD40L+ cells/CD4+ T cells after stimulation of whole blood with pools of E. coli proteins.

RESULTS

The E. coli-specific Th1 response was significantly reduced in CD patients and to a lower extent also in AS patients.

CONCLUSIONS

E. coli is a target for polyclonal Th1 responses in healthy individuals. The impairment of these responses in CD and AS patients might be due to recruitment of enterobacteria-specific Th1 cells to the gut or might reflect inadequate priming of adaptive immune response.

Identification of the predominant antigenic epitopes in intestinal flora in IBD

The normal intestinal flora is required for the development of intestinal inflammation in animal models of inflammatory bowel disease (IBD). In humans, several studies indicated a potential association of Escherichia coli (E. coli) with IBD. In addition, we have shown that T-cell clones of IBD patients cross react toward different enteric bacterial species and thus likely respond to conserved bacterial antigens. Therefore, we hypothesized that highly conserved E. coli proteins might be a reasonable candidate to screen for abnormal T-cell responses in IBD. We used high-throughput techniques for cloning, expression, and purification under native conditions of a set of 271 conserved proteins of E. coli, of which 196 were used for whole blood stimulations to assess peripheral T helper (T(H))-cell responses. In addition, because of the association of an adherent-invasive E. coli with Crohn's disease (CD), we included 13 pathogenicity factors of E. coli in the study. We observed that pools of these conserved E. coli proteins less frequently induced interferon-gamma (IFNgamma) production in peripheral T(H) cells in patients with CD and ankylosing spondylitis (AS) compared with healthy controls. In addition, lower percentage of patients with CD and AS responded toward single proteins. The reason for the decreased frequency of an in vitro T(H)-cell IFNgamma response toward E. coli proteins in peripheral blood of CD and AS patients, e.g., increased suppression needs to be clarified.