The effect of reduced radiation on serum IgG3 reconstitution at 12, 18, 24, and 30 weeks posttransplant (A) and on the response to the T-cell–independent antigen NP-Ficoll (B) is shown. Concentrations are given in micrograms per milliliter and the radiation doses are indicated on the x-axis. All mice received 0.5 × 10⁶ total cells, of which 5% were normal. WT, normal CBA/J mice; xid, CBA/N mice. Each group contained 5 mice, except for the xid controls, which contained 4 mice.