Bone marrow perisinusoidal B cells respond to multivalent antigens in an antigen-specific manner in the complete absence of lymphoid organs. (A) Analysis of CD95⁺PNA⁺CD45R⁺ B cells in the bone marrow of splenectomized wild-type and LTα^−/− mice. Sham mice were injected with saline, whereas test mice were injected with SL3261 bacteria. The plots shown are representative of 3 mice in each group. (B) ELISPOT assay for IgM antibody-forming cells in the bone marrow against LPS and flagella antigen in splenectomized wild-type (C57BL/6) and LTα^−/− mice previously challenged intravenously with SL3261 bacteria. UI indicates mice that were not challenged; I, mice that received an intravenous challenge. Error bars denote standard error of the mean.