Immunoglobulin levels in peripheral blood of naive and immunized APEX2-null mice. (A) Concentrations of IgM, IgG, and IgA of 11-week-old naive wild-type (WT, n = 7) and APEX2-null mice (KO, n = 8). Concentrations of immunoglobulins in serum are shown with box-and-whisker plots. In each plot, the box is bound top and bottom by upper and lower quartiles, and the statistical median is shown as a horizontal line within the box. The whiskers extend outward from the box to the farthest points that are not outliers (circles). The concentration of each immunoglobulin (IgM, IgG, or IgA) in serum of APEX2-null mice was not significantly different from that of wild-type mice (Mann-Whitney U test, P > .05). (B) Time-dependent induction of antigen-specific antibodies in wild-type and APEX2-null mice after immunization with OVA. Eleven-week-old wild-type (n = 6) and APEX2-null (n = 6) mice were immunized with 300 μg OVA on days 0, 21, and 35 as shown by arrows. Animals were separated into 2 groups, and serum was collected biweekly from each group of mice on alternate weeks. The mean titers of anti-OVA IgM and IgG of wild-type mice (○) and APEX2-null mice (▴) are shown as line graphs. (C) OVA-specific antibodies in wild-type and APEX2-null mice immunized with OVA for 4 weeks. A total of 8 mice were immunized with OVA as described in panel B. The titers of their serum anti-OVA IgM and IgG are shown with box-and-whisker plots. Differences between wild-type and APEX2-null mice were not statistically significant (Mann-Whitney U test, P > .05).