Regenerative Potential of Immunocompetent Cells: III. Recovery of primary antibody-forming potential from X-irradiation. The role of the thymus

The experimental data are consistent with the notion that the immune progenitor cell pool initially stimulated in the primary antibody response is distinct from that stimulated in the secondary or anamnestic response. A major factor responsible for the long-lasting immunologic inadequacy of irradiated animals appears to be a chronic deficiency in immunocompetent cells. The capacity to form 7 S antibody was more heavily suppressed by x-irradiation than was the capacity to form 19 S antibody. This preferential suppression of the 7 S response was seen throughout the recovery phase. In thymectomized mice irradiated with 850 r and treated with isologous bone marrow, recovery of the 7 S antibody response was virtually abolished, whereas the 19 S hemagglutinin response recovered substantially. Recovery of antibody-forming capacity from x-ray exposures as high as 1000 r does not require the presence of the thymus; primarily the rate of recovery appears to be thymus-dependent. These observations were made in two different mouse strains with rat and sheep RBC used as test antigens. Recovery from antigen competition was found to be independent of the thymus.