Peritoneal B-1 cells switch in vivo to IgA and these IgA antibodies can bind to bacteria of the normal intestinal microflora.

Abstract

A prominent feature of the mucosal immune system is formed by IgA secreting cells located in the lamina propria, immediately beneath the epithelium. In the intestine of the mouse at least 15 million cells secrete IgA into the surrounding connective tissue [1]. Subsequently, secretory IgA is transported across the single layer of epithelial cells and pumped into the gut lumen. Here, IgA can bind to food antigens and to the numerous microorganisms (in humans about 1011 bacteria per gram colon contents!). This interaction may help to prevent invasion and infection of the body with microbes, e.g. by preventing binding to the mucus layer and the epithelial cells (‘immune exclusion’).