Inflammation of the small intestine

The epithelium of the small intestine is constantly exposed to a range of microorganisms and foreign substances. It provides both a physical and immunological barrier against these exterior challenges. The cells of the epithelium are constantly scanning the environment for antigens to be able to quickly react to pathogens. Because of this constant exposure, lymphocytes are always present in the intestine at approximately 6-40 lymphocytes per 100 epithelial cells.

If an antigen is detected by a lymphocyte, the immune cell sends out immunostimulators and a signaling cascade is initialized. More lymphocytes are recruited and they migrate into the inflamed tissue. Radical changes of the epithelial architecture lead to a decreased length of the villi, apoptosis of epithelial cells, and enlarged crypts. These changes decrease the surface area of the small intestine, which in turn leads to a decrease in the absorption of nutrients.

Figure 1: Inflammed villi with invading lymphocytes (marked in blue).

Inflammation of the small intestine can be caused by food borne pathogens such as Salmonella or buy autoimmune disease such as coeliac disease.