Multivalent cross-linking of membrane Ig sensitizes murine B cells to a broader spectrum of CpG-containing oligodeoxynucleotide motifs, including their methylated counterparts, for stimulation of proliferation and Ig secretion

We have previously reported that a cells that are activated by multivalent but not bivalent membrane Ig cross-linking ligands synergize with various B cell activators culminating in enhanced B cell proliferation, In this stud y we asked whether a cells that are activated by a multivalent mig cross-li nking agonist could respond to oligodeoxynucleotides (ODN) containing non-s timulatory motifs, Earlier reports have shown that ODN containing a CpG mot if in which the cytosine is unmethylated and is flanked by two 5' purines a nd two 3' pyrimidines induce high levels of B cell activation, while ODN wh ose CpG are methylated or flanked by sequences other than the optimal two 5 ' purines and two 3' pyrimidines were non-stimulatory. In this manuscript w e show that when B cells are stimulated in vitro with dextran-conjugated an ti-IgD antibodies (anti-IgD-dex), as the multivalent mig ligand, their prol iferation is enhanced and they can be induced to secrete Ig in response to ODN containing various non-optimal motifs, both methylated and non-methylat ed, Furthermore we could induce synergistic levels of proliferation with co ncentrations of anti-IgD-dex that were in the picomolar concentration range and with concentrations of ODN that were 10- to 100-fold less than previou sly reported to be necessary for mitogenic activity, These data provided a model to explain how low concentrations of a multi-epitope-expressing micro organism in the context of mammalian (methylated) or microorganism (non-met hylated) DNA can lead to dysregulated B cell proliferation and Ig secretion .