Plasmacytoid dendritic cells and RNA-containing immune complexes drive expansion of peripheral B cell subsets with an SLE-like phenotype.

Background: Hyperactive B cells and a continuous interferon (IFN)-α production by plasmacytoid dendritic cells (pDCs) play a key role in systemic lupus erythematosus (SLE). We asked whether the interaction between B cells and pDCs stimulated with RNA-containing immune complexes affects peripheral B cell subsets.
Methods: B cells and pDCs were isolated from blood of healthy individuals and stimulated with immune complexes consisting of SLE-IgG and U1snRNP (RNA-IC). Expression of cell surface molecules as well as IL-6 and IL-10 production were determined by flow cytometry and immunoassays. Gene expression profiles were determined by a NanoString nCounter expression array.
Results: We found a remarkable increase of double negative CD27-IgD- B cells, from 7% within fresh CD19+ B cells to 37% in the RNA-IC-stimulated co-cultures of B cells and pDCs, comparable to the frequency of double negative B cells in SLE patients. Gene expression analysis of the double negative CD27-IgD- and the CD27+IgD- memory B cells revealed that twenty-one genes were differentially expressed between the two B cell subsets (≥ 2-fold, p<0.001). The, IL21R, IL4R, CCL4, CCL3, CD83 and the IKAROS Family Zinc Finger 2 (IKZ2) showed higher expression in the double negative CD27-IgD- B cells.
Conclusion: The interactions between B cells and pDCs together with RNA-containing IC led to an expansion of B cells with similar phenotype as seen in SLE, suggesting that the pDC-B cell crosstalk contributes to the autoimmune feed-forward loop in SLE.