Latest In vitro and in vivo models of celiac disease (1)
Ingestion of wheat-derived gluten by celiac patients results in immune mediated injury of the intestines that is characterized by intestinal permeability, villous atrophy, and an inflammatory infiltration of the lamina propria that consists primarily of lymphocytes and plasma cells. The increased intestinal permeability in celiac disease allows for paracellular transfer of gluten derived peptides to the lamina propria, resulting in the presentation of gluten derived peptides to, and subsequent activation of, T cells. Gluten derived peptides can also stimulate non-T cells directly, including epithelial cells, monocytes, and dendritic cells. These cells can produce a variety of inflammatory cytokines in response to stimulation with gluten. The stimulation of both non-T cells (innate immune response) and T cells (adaptive immune response) by gluten contribute to the development of intestinal inflammation in celiac disease.
In Vitro Models of Celiac Disease
Cell Lines
In vitro models of an epithelial layer consistent with celiac disease include Caco-2 and IEC-6 epithelial cell lines. A peptide derived from the α-gliadin molecule, called p31–p43 (a stimulator of innate responses in celiac disease), induces expression of cell surface IL-15 by Caco-2 cells, and thereby stimulates the proliferation of T cells. When Caco-2 cells are exposed to Bacteroides fragilis and gliadin, there is a subsequent increase in intestinal permeability as well as increased production of TNFα and IL-1β. With respect to monocytes responding to gluten in an innate fashion, monocytes cultured with proteolytic fragments of gliadin (PT-gliadin) will produce the inflammatory cytokines TNFα and IL-8. Similarly, when DCs are cultured with PT-gliadin, they secrete the inflammatory cytokines IL-6, IL-8, and TNFα.
APC/T Cell Mixes
Mixes of APCs with intestinally derived T cells from celiac patients have been used extensively to model the presentation of gluten derived epitopes in celiac disease. T cells from DQ2.2+ celiac patients recognize a glutenin derived epitope that is entirely different from the α-gliadin derived 33mer peptide found to be very immunogenic in DQ2.5 celiac patients.
Mucosal Biopsy Cultures
intestinal biopsy cultures extracted from celiac patients incorporate all of the cell-cell interactions present in the small intestine. Studies done with this model range from analyzing the T cell stimulatory potential of different fractions of gluten and gliadin. The mucosal biopsy culture model proves to be quite useful in determining both innate and adaptive responses to gluten derived from alternative cereals, and as such their potential toxicity for celiac disease patients.
In Vivo Models of Celiac Disease
Induced Models
Germ-free Wistar AVN rats are administered gliadin immediately after birth. This leads to shortening of villi, crypt hyperplasia, and increased numbers of intestinal CD8αβ+ IELs. that feeding the rats B. longum results in the up-regulation of anti-inflammatory processes and that this is enough to partially ameliorate gliadin induced stress when both B.longum and gliadin are administered to the rats. Co-administration of Shigella or E. coli with gliadin resulted in an increase in the impairment of tight junctions and resulted in translocation of gliadin peptides into the lamina propria. Transferring CD4+CD25-CD45RBlow cells from gliadin sensitized mice to recipient Rag 1−/− mice was archived. Balb/c mice that were bred for three generations on a gluten free diet; subsequent offspring were then weaned and raised on a gluten free chow for up to 10 weeks of age. The resultant mice were placed onto a standard chow for 30 days. These mice had increased numbers of infiltrating CD3+ IELs with a decreased (villous height)/(crypt depth) ratio.
Transgenic Models
These mice have demonstrated that the HLA molecules DQ8 and DQ2 can contribute to the development of a potent inflammatory T cell response against gliadin, but that this alone is not sufficient for the development of gluten dependent enteropathy characterized by shortened villi. Perturbations of the innate immune response in the intestine are necessary for features of
gluten dependent enteropathy to develop, including the administration of cholera toxin, which acts as an adjuvant, and indomethacin, which causes small intestinal pathology. Poly I:C stimulates the innate immune response through TLR3, and was used in a mouse line in which TG2 was knocked out.