Functional characteristics of the veiled cells in afferent lymph from the rat intestine.

Non-lymphoid veiled cells (VC) in the thoracic duct lymph from mesenteric lymphadenectomized rats have been studied by light microscopy, enzyme histochemistry and scanning electron microscopy. These cells arise in the afferent lymph from the intestine. They have been semi-purified and examined for expression of Ia antigens using an indirect immunoperoxidase technique and monoclonal antibodies. Accessory cell function necessary for mitogen-induced blastogenesis in the thoracic duct lymph from these animals has been correlated with the presence of VC by depletion and reconstitution experiments. Similar results were obtained with lymphocyte suspensions from other rat lymphoid organs and they are contrasted with those from studies on mouse lymphoid cells. Antigen presentation in a secondary in vitro lymphoproliferative assay was also depleted from immunized lymph node cells by removal of endogenous VC and can be reconstituted in a dose-dependent fashion with antigen-pulsed VC from afferent intestinal lymph. In contrast, reconstitution of both mitogen-induced blastogenesis and antigen-induced lymphoproliferation with peritoneal exudate cells was poor, while at high multiplicities of added macrophages, such cells were inhibitory. Afferent intestinal lymph VC were found to transport bacteria and bacterial antigen in rats infected with Salmonella typhimurium. The results are discussed in relation to the lineage of the VC in intestinal afferent lymph, their function as accessory cells and their possible physiological role in transporting antigens from the gut to its regional lymph nodes.