</doi><aid>20052093</aid>Innate secretory antibodies protect against natural Salmonella typhimurium infection

JEM © The Rockefeller University Press $8.00 Vol. 203, No. 1, January 23, 2006 21–26 www.jem.org/cgi/doi/10.1084/jem.20052093 21 One of the most characteristic features of the mucosal immune system of most mammals is the dominant presence of SAbs, particularly secretory IgA (SIgA), an antibody class unique to the mucosae. At least 80% of all Ig-producing plasma cells in the body are found in the intestinal lamina propria, and most of these cells produce polymeric IgA (pIgA; mainly as dimers) (1, 2). Both pIgA and pentameric IgM are actively transcytosed across the secretory epithelium that lines the mucosal surfaces to external secretions after binding to the polymeric Ig receptor (pIgR), a glycoprotein expressed on the basolateral surface of secretory columnar and crypt epithelial cells, also called membrane secretory component (3–6). Some 40 mg SIgA kg-1 body weight is transported to the gut lumen by the pIgR every day in a healthy adult human (7). The development of the gastric-associated lymphoid tissue (GALT)