NEGATIVE SELECTION OF MULTIREACTIVE B-CELL CLONES IN NORMAL ADULT MICE

In the absence of intentional immunizations. normal mice produce natur al antibodies that react with a variety of self and foreign antigens. We have now addressed the putative physiological selection of such rea ctivities and some of their clonal characteristics, by analyzing antib odies produced by B cells at different stages of differentiation. Usin g an antigen-specific spot-enzyme-linked immunosorbent assay (ELISA) w ith a panel of self and foreign antigens,we found that newly formed B cells, either from adult bone marrow or from newborn spleen, contain t he highest frequencies of IgM antibodies with reactivities towards the panel. Resting peripheral B cells show lower frequencies of such anti bodies, that are lowest among naturally activated splenic plasma cells . Analyses of monoclonal IgM antibodies derived from lipopolysaccharid e-stimulated bone marrow and spleen cell hybridomas in normal mice sho w that the majority of reactivities scored in spot-ELISA originate fro m multireactive IgM clones. In Western blots against a large number of self antigens, each multireactive IgM antibody studied shows a unique and specific pattern of reactivity. We conclude that multireactive B cell clones are very frequent in the emergent repertoires of newborns and adults, but are subsequently negatively selected from bone marrow to periphery. and from the available repertoire to that of natural pla sma cells. It, thus, seems that multireactivity of natural antibodies is not a positively selected property, but represents the sum of uniqu e multireactive clones that have escaped inactivation or deletion.