Mouse splenic B lymphocyte activation using different activation stimuli induces in vitro splicing of tumor necrosis factor-α nuclear pre-mRNA

The pleiotropic functions of tumor necrosis factor-alpha (TNFα) have brought considerable attention in the past decade to its physiological and pathological roles in inflammatory and autoimmune diseases. However, little is known about how the production of TNFα is regulated at the transcriptional and translational levels in immune cells such as T and B lymphocytes. Our previous study demonstrated that unspliced “pre-mRNA” of TNFα is present in resting T cells. Initiation of splicing of TNFα pre-mRNA to mature mRNA requires T cell activation, which is unique and necessary for TNFα production when compared to its production in mononuclear phagocytes, including different lineages of macrophages (Mϕ) and dendritic cells (DC). In this study, we further demonstrate that resting mouse B cells also contain pre-existing TNFα mRNA. The physiological process of B cell activation induced by (1) either the cross-linking of the B cell receptor (BCR) or CD40, (2) treatment with LPS, or PMA plus ionomycin, induces TNFα mRNA splicing in vitro. The kinetic response of TNFα splicing in B cells is much slower when compared to that in activated T cells. Studies using well-known kinase inhibitors demonstrated that MAP kinase kinase (MEK) and protein kinase C (PKC) are required for TNFα splicing upon stimulation through the BCR. These studies demonstrate that the production of TNFα in activated B cells is regulated differently than in activated T cells, and these differences may allow for the selective inhibition of TNFα in various autoimmune diseases depending on the mechanism of action of the selected anti-TNFα therapy.