CpG oligodeoxynucleotides overcome the unresponsiveness of neonatal B cells to stimulation with the thymus-independent stimuli anti-IgM and TNP-Ficoll.

Neonates are very vulnerable to pathogenic encapsulated bacteria due to their inability to mount an antibody response to capsular polysaccharides, which are thymus-independent type 2 (TI-2) antigens (Ag). Oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides induced neonatal B cells to proliferate to anti-IgM, a TI-2 stimulus. CpG ODN inhibited the spontaneous and B cell receptor-mediated apoptosis of neonatal B cells and reduced the amount of the pro-apoptotic Bcl-xS, strongly correlated with anti-IgM-induced apoptosis of neonatal B cells. CpG ODN protected neonatal B cells from apoptosis by down-regulation of the Bcl-xS protein. Neonatal B cells underwent polyclonal differentiation upon stimulation with CpG ODN, but unlike in adult B cells, this was not preceded by IL-6 secretion. CpG ODN stimulated neonatal B cells to mount an Ag-specific antibody response to TNP-Ficoll, another TI-2 Ag. Thus CpG ODN could provide a novel approach to induce the immune system in neonates to respond to harmful encapsulated bacteria.