Abetalipoproteinemia is a human genetic disease that is characterized by a defect in the assembly or secretion of plasma very low density lipoproteins and chylomicrons. The microsomal triglyceride transfer protein (MTP), which is located in the lumen of microsomes isolated from the liver and intestine, has been proposed to function in lipoprotein assembly. MTP activity and the 88-kilodalton component of MTP were present in intestinal biopsy samples from eight control individuals but were absent in four abetalipoproteinemic subjects. This finding suggests that a defect in MTP is the basis for abetalipoproteinemia and that MTP is indeed required for lipoprotein assembly.

MICA molecules interact with the NKG2D-activating receptor on human NK and CD8 T cells. We investigated the participation of the MICA/NKG2D pathway in the destruction of intestinal epithelium by intraepithelial T lymphocytes (IEL) in Celiac disease and its premalignant complication, refractory sprue. We show that MICA is strongly expressed at epithelial cell surface in patients with active disease and is induced by gliadin or its p31-49 derived peptide upon in vitro challenge, an effect relayed by IL-15. This triggers direct activation and costimulation of IEL through engagement of NKG2D, leading to an innate-like cytotoxicity toward epithelial targets and enhanced TCR-dependent CD8 T cell-mediated adaptive response. Villous atrophy in Celiac disease might thus be ascribed to an IEL-mediated damage to enterocytes involving NKG2D/MICA interaction after gliadin-induced expression of MICA on gut epithelium. This supports a key role for MIC/NKG2D in the activation of intraepithelial immunity in response to danger.

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The gut epithelium favors the development of T cells that express NK receptors. In active celiac disease, there is a specific and selective increase of IELs expressing CD94, the HLA-E-specific NK receptor that may be related to T-cell receptor activation and/or interleukin 15 secretion.