The natural history of the cells producing IgA in the gut.

The IgA-secreting cells in the lamina propria of the small intestine are derived from large lymphocytes which enter the blood by way of the thoracic duct and then migrate into the gut where they complete their differentiation into plasma cells. Three aspects of this cellular traffic have been examined in rats. 1. The cells in thoracic duct lymph which give rise to IgA-secreting cells in the lamina propria are among those which carry surface IgA. Blast cells lacking surface immunoglobulin migrate mainly into the Peyer's patches and do not contribute to the IgA response. 2. Studies on a secondary antibody response to cholera toxoid, in which the challenge was given into a Thiry-Vella loop, showed that the antibody-containing blast cells in thoracic duct lymph were derived from Peyer's patches. The mesenteric nodes contributed little, if anything, to the cellular response in the lymph. 3. The idea that secretory component is a signal for the emigration of large lymphocytes from the blood into the lamina propria lacks experimental support. Secretory component does not bind to the IgA on the surface of thoracic duct cells. On the other hand, antigen in the gut may play an important part in immobilizing large lymphocytes in the lamina propria once they have migrated.