Purpose/Objective Inappropriate B cell receptor (BCR) signalling contributes to the activation of auto-antibody-producing B cells in many autoimmune diseases. These diseases results from a break in B-cell tolerance which is normally maintained by the mechanisms of anergy, receptor editing and deletion. We previously showed that IVIg modulates many B cell responses through a sialic acid-CD22 lectin interaction (Séité, Blood 2010, Séité, J Autoimmunity, 2011). Here, we reasoned that IVIg could modulate B-cell fate and may render autoreactive B cells tolerant through induction of a functional unresponsiveness response to BCR stimulation.
Material and Methods Tonsilar B-cells were stimulated in the presence of different fractions of IVIg. We analysed subsequent responses to BCR stimulation by confocal microscopy, quantitative RT-PCR, FACS and Western-blot analysis.
Results First, we observed that up-regulation of costimulatory molecules CD86, CD80 and CD40 induced by BCR cross-linking was down-regulated after IVIg incubation and was associated with a massive reduction of tyrosine phosphorylation. Low mobilisation of intracellular Calcium, which is a hallmark of anergy, was also observed in IVIg-treated B cells. Next, we observed that following BCR stimulation, IVIg blocks BCR aggregation within lipid rafts and increases its internalisation. Consequently, BCR stimulation is not achievable and results in a low activation of the PI3K-Akt signalling pathway. Finally, we demonstrated that IVIg down-regulates NFκB activation and promotes NFAT transcription factors entry in the nucleus. These findings demonstrated that IVIg induces a selective transcriptional programme, allowing nuclear signals to be independently activated, leading to alternative B cell fates.
Conclusions Our data suggest that IVIg could induce B cells to adopt a state that results in a functional silencing, also called anergy. Our findings provide insights into the effectiveness of IVIg in treating pathologies associated with the loss of B cell tolerance. We also describe a new model to explore the complexity of positive versus negative selection in human B cells.