Increased antibody production in PEG-ADA–treated ADA^−/− mice. (A) ELISA assessing antibody production against ADA in PEG-ADA (n = 7), GT (n = 6), and BMT (n = 10) treated ADA^−/− mice compared with ADA^+/+ mice (n = 7) and 3-week-old ADA^−/− mice (n = 3); scatter plot; horizontal bars represent mean. (B) ELISA assessing autoantibody production against platelets in PEG-ADA (n = 10), GT (n = 6), and BMT (n = 10) treated ADA^−/− mice compared with ADA^+/+ mice (n = 7) and 3-week-old ADA^−/− mice (n = 5); scatter plot; horizontal bars represent mean. (C) Autoantibody production directed against thyroid tissue in PEG-ADA but not GT- and BMT-treated ADA^−/− or ADA^+/+ mice. (D) Thyroid damage occurring in autoantibody-producing PEG-ADA–treated mice compared with a GT- or BMT-treated ADA^−/− and WT control. (E) Percentage of apoptotic Ccl3-positive nuclei in the thyroid of PEG-ADA–treated ADA^−/− (n = 7) compared with GT (n = 5) and BMT (n = 5) treated ADA^−/− and ADA^+/+ mice (n = 5). Data are mean ± SD. *P = .05. (F) Concentration of TSH in sera of PEG-ADA–treated ADA^−/− mice (n = 14) compared with ADA^+/+ mice (n = 8). Data are mean ± SD. *P = .05.