The role of surface ig binding in the activation of human B cells by phosphorothioate oligodeoxynucleotides.

Phosphorothioate oligodeoxynucleotides (sODNs) can induce T-cell-independent polyclonal activation of human B cells by a mechanism that depends on both sequence and back-bone structure. Because matrix-bound as well as soluble sODNs are mitogenic, this stimulation may result from the engagement of surface receptor(s). In order to investigate whether surface immunoglobin (Ig) could be a receptor for sODNs, the interaction of sODNs-fluorescein isothiocyanate (FITC) with Ig-coated beads was examined. sODNs specifically bound to human IgM and IgG. Moreover, binding of sODN to human B cells induced temperature-dependent capping of bound receptors and colocalization of FITC-sODN and IgM into aggregated caps on the surface of human B cells. A role of surface Ig was furthermore shown by observations that antibody-mediated capping of B-cell surface IgM or IgD inhibited subsequent binding of sODNs and that the capacity of sODN to stimulate human B cells was blocked by excess IgM or IgG, by nonstimulatory antibodies to sIgM, as well as by a variety of negatively charged molecules. Together, these results indicate that sODNs engage surface Ig by charge-charge interactions that lead to activation of human B cells.