Studies of the immunological capacity of germ-free mouse radiation chimeras. II. Thymus cell function in a humoral immune response to sheep erythrocytes

Experiments described here were undertaken to determine the reason for the depressed humoral immune response in germ-free mouse allogeneic radiation chimeras. Indirect immunofluorescence using the theta (θ) antigen as a marker demonstrated that about 10% of the nucleated cells in the spleen of both allogeneic and syngeneic chimeras bear the θ antigen. One type of in vivo cell transfer assay employed to determine the capacity for “helper” function of thymocytes revealed that allogeneic chimera thymocytes were only 7–18% as efficient in “helper” function as normal thymocytes. A second type of in vivo cell transfer assay demonstrated that the presence of intact normal thymic stroma had no effect on the “helper” inefficiency of thymocytes obtained from allogeneic radiation chimeras.