Antigen transport. I. Demonstration and characterization of cells laden with antigen in thoracic duct lymph and blood.

Thoracic duct lymph (TDL) of nonimmune rats and mice was examined for the presence of antigen-carrying cells immediately following a single injection of 125I-labelled or fluorescence-labelled serum protein antigens. Small numbers of cells laden with antigen (approximately 1/2000 to 1/5000) were identified in TDL and blood by autoradiography or fluorescence microscopy. The antigen-laden (Ag-L) cells resembled macrophages in that a large number adhered to plastic, they phagocytosed bacteria or a particulate dye, were non-specific esterase positive, radioresistant and could take up more than one antigen at one time in vivo. Surface phenotyping using monoclonal antibodies against rat cell markers established that Ag-L cells did not express Ia determinants. The results suggest the existence of a subpopulation of macrophage-related cells that may be involved in the transport of antigen and in stimulation of antibody responses.