This last phenomenon was also observed when twofold, fourfold or eightfold lower concentrations of blocking peptides against pNF-κB p65 or pSTAT3 were used (data not shown). To assess the roles of NF-κB p65 and STAT3 in the later processes of cell differentiation (i.e. the final production of Ig), we sought to stimulate purified blood B cells with sCD40L + IL-10 while simultaneously blocking either one or both of the

transcription pathways using specific blocking peptides against pNF-κB p65 or pSTAT3. The pNF-κB p65 blocking peptide led to a modest, but significant, 20% decrease in pNF-κB p65. The anti-pSTAT3 peptide alone had nearly the same effect, resulting in an 18% reduction in pNF-κB p65. Together, the blocking peptides against pNF-κB p65 and pSTAT3 reduced NF-κB p65 phosphorylation Apoptosis inhibitor LDK378 by 28% (Fig. 8b). Reciprocally, the anti-pSTAT3 peptide significantly reduced pSTAT3 by 45% (Fig. 8c), while the anti-pNF-κB p65 peptide reduced it by 30%. Combined, these blocking peptides reduced pSTAT3 by 73%. IgA production was completely inhibited; however, phosphorylation of NF-κB and STAT3 was not blocked completely. These observations were probably due to neo-phosphorylation induced by other stimuli or by the oscillations in NF-κB signalling, as could have been

expected [32]. These data indicate that there is probably co-operation between Protein kinase N1 the various transcription factor pathways, and in particular, an NF-κB influence on the STAT3 pathway. Furthermore, these results suggest that sCD40L acts first on purified B cells, promptly activating the classical NF-κB pathway and inducing IL-10R expression (experiments and data not shown), which then renders the STAT3 pathway reactive to IL-10 signalling. We aimed

to elucidate some of the molecular pathways involved in providing purified B lymphocytes with the differentiation signals of non-cognate T cell surrogates, i.e. the classical sCD40L/CD40 + IL-10/IL-10R signals, leading to the skewed production of Ig towards IgA. We deliberately excluded from this investigation the addition of exogenous TGF-β, described classically as an IgA differentiation factor in a number of studies, on the basis of preliminary experiments (Fig. 2a and data not shown), having shown that TGF-β antagonized the differentiating role of sCD40L and IL-10 towards IgA class switch in this culture system. However, because these experiments were performed initially by culturing purified B lymphocytes in FCS-containing medium, the possibility that TGF-β eventually present in this serum may have biased our results was considered, as has been described, e.g. for the plasticity of T helper 17 (Th17) responses [33]. TGF-β1 induces IgA switching and secretion in stimulated B lymphocytes in mouse spleen. This has also been shown for IgG2b using mouse spleen B cells.