Contribution of c-Maf to regulatory B cells and antibody-secreting cells

PROJECT SUMMARY Regulatory B cells are involved in many pathophysiological processes, such as promoting tolerance in autoimmunity and organ transplantation, but also reducing immune responses to cancer.

Overall, many studies indicate that regulatory B cells, like regulatory T cells, play a crucial role in regulating the immune system in many circumstances.

A growing body of evidence highlights the strong heterogeneity as well as a high functional plasticity of regulatory B-cell subsets, which challenge a unique and stable definition. However, a common function of regulatory B cells is to produce the immunoregulatory cytokine IL-10.

While significant attention has been focused on defining the multiple phenotypes of regulatory B cells, there remains a critical need to understand the molecular triggers of regulatory B-cell functions.

In experiments performed with human blood B cells, we have obtained preliminary data pointing to specific molecular drivers that control the generation of IL-10-producing regulatory B cells.

Among them, we noticed the transcription factor c-MAF, a factor belonging to the activator protein-1 (AP-1) superfamily and known to modulate cytokine production in T cells and macrophages. To date, a function of c-MAF in B cells has not been reported.

Results from our analyses suggest that in humans, c-MAF acts as an early regulator of the generation of IL-10-producing B cells with a plasmablast phenotype.

In addition, a recent publication together with publicly available gene transcription data indicate that c-Maf can bind the Il10 gene promoter in murine B cells and that, among all mouse B-cell subsets, is most highly transcribed in plasmablasts.

The present study aims to use a tissue- specific gene knock-out mouse model to explore and establish in vivo the role of c-Maf in the generation of antibody-secreting cells and IL-10-producing plasmablasts.

Specifically, we propose to use established c-Maf- floxed mice and CD19-Cre mice to generate B-cell conditional c-Maf knock-out mice to test the following: 1) the function of c-Maf in the steady-state development of plasmablasts and the generation of antibody-secreting plasmablasts and plasma cells after immunization; and 2) the contribution of c-Maf to the generation of IL-10- producing regulatory B cells and plasmablasts.

Furthermore, these studies will use a Salmonella infection model to test whether c-Maf contributes to the development of functional regulatory B cells that reduce critical immune responses.

The proposed studies are significant because they are the first to investigate the role of c- Maf in B-cell biology and because they will lead to a better understanding of the molecular processes regulating, on one side, the development of plasmablasts and humoral immunity, and on the other, the generation of regulatory B cells that contribute to exacerbated or ineffective immunity.