Absence of Igs in AID^−/−µS^−/− mice correlates with enlarged secondary lymphoid organs and increased numbers of B cells. Age-matched WT C57Bl/6, AID^−/− (AID), μS^−/− (μS), and AID^−/−μS^−/− (AIDμs) mice were analyzed for (A) serum levels of IgM and total IgGs by ELISA. (B) Picture showing the relative size of spleens (top), mLNs (bottom left), and the 2 inguinal, axillary, and brachial LNs (right, top to bottom) taken from one mouse of each group. (C) The total B-cell numbers from spleens of 8- to 12-week-old age-matched mice were analyzed by flow cytometry. Each dot represents one animal; *P ≤ .05, **P ≤ .01, ***P ≤ .005.