Cellular sites of immunoglobulins . VI. Localization of immunoglobulins in the human thymus.

IgG-, IgM and IgA-containing cells in the human thymus and mesenteric lymph nodes were studied by direct, double-antibody immunofluorescence techniques. Ig-containing cells were identified in the thymic medulla but not in cortical or paracortical zones. About 93 percent of the medullary Ig-containing cells were IgG-containing (vs. 5 percent IgM containing and 2 percent IgA - containing). By contrast, lymph nodes contained about 53 percent IgG, 31 percent IgA and 16 percent IgM type immunocytes. In addition, Ig-containing cells were about one-tenth as numerous in thymus as in lymph nodes.