Antigen presenting cells and T cell interactions in the gastrointestinal tract.

Dendritic cells make up less than 1% of the cells in lymph nodes and tissues, but they are critical in initiating and directing T cell immune responses. In the gut, with exposure to myriad food and bacterial antigens, they probably control T cell unresponsiveness to food antigens and T cell hypersensitivity in disease situations. The need for the immune system to 'know' gut luminal antigens is demonstrated by the fact that dendritic cells send processes through the epithelium and directly sample antigens in the gut lumen. We present evidence that type I INF made by plasmacytoid dendritic cells may be important in coeliac disease.