The role of post-transcriptional control of CD40L on the development of autoimmune disorders
Creators: name: Prado De Maio, Diego
Publisher: name: No Publisher Supplied
Year: 2024

description: Control of expression of immunostimulatory molecules is vital to the prevention of a break in central or peripheral tolerance that can lead to the development of autoimmune disorders. Among the many signals involved in the activation of adaptive immunity, CD40L on CD4+ T cells binding to CD40 on antigen-presenting cells (APCs) and B cells in particular has been identified as a key interaction and point of control for fine-tuning immune responses. Ligation of CD40L by B cells is critical for the formation of germinal centers, affinity maturation, and terminal differentiation into plasma or memory B cells, all processes that have been found to be pathogenically enhanced in systemic lupus erythematosus (SLE). Thus, regulation of CD40L expression is critical to ensure stimulation of B cell activation pathways when appropriate and makes CD40L an attractive therapeutic target for treating autoimmune disorders. Our lab has previously described a locus on the 3’ UTR of CD40L mRNA that is responsible for extended stability of the message during CD4+ T cell activation by binding of a complex nucleated by the polypyrimidine tract binding protein, PTBP1. Removal of this stability element in CD40LΔ5 mice leads to decreased CD40L on CD4+ T cells and causes significant disruption to a normal T-dependent response by basis of disrupted germinal center formation, decrease in germinal center B cell survival, terminal differentiation down plasma and memory fates, and decreases in antibody affinity and overall titers of switched antibodies. We decided to investigate the effect that the CD40LΔ5 mutation could have in mouse models of SLE, given the importance of autoreactive B cell maturation and autoantibody formation in the pathogenesis of disease. For this, we implemented two well characterized models of human SLE in mice. The first, pristane-induced lupus (PIL), is initiated by injection of the powerful hydrocarbon adjuvant pristane that over the course of six months generates a state of chronic inflammation that allows a break in tolerance and furthers autoreactive B cell activation and enrichment, resulting in high titers of anti-self antibodies and deposition of immunocomplexes in the kidney glomeruli. The second model is an inducible chronic graft-versus-host disease (cGVHD) that resembles SLE by the production of anti-dsDNA antibodies due to the alloactivation of host B cells following adoptive transfer of histoincompatible CD4+ T cells from bm12 mice. bm12 mice harbor a small mutation in the antigen-presenting major histocompatibility complex class II (MHC-II) that results in allorecognition between CD4+ T cells from bm12 donor mice and the non-bm12 recipient’s APCs.Using our CD40LΔ5 mice, we hypothesized that a reduction in CD40L would result in an ameliorated disease by preventing proper development of autoreactive B cells. Surprisingly, in both of these models, we observed a consistent sex-dependent increase in B cell activation and differentiation as well as increased autoantibody titers in female CD40LΔ5, while mutant males had little to no protection from disease. With the PIL model, we closely assessed the resultant disease through observation of increased immunocomplex deposition of IgG in the glomeruli and found increased deposition in CD40LΔ5 female mice over WT. The bm12 cGVHD model, with a significantly shorter induction time, allowed us to more effectively control the effect of the CD40LΔ5 mutation in a strictly follicular helper T cell driven autoimmune response. With this model, we were further able to identify differences in the cytokine profile of donor and host CD4+ T cells and observed significant skewing between Th1 and Th2 subsets, as well as increased cells expressing the pro-inflammatory cytokines IL-17a and IL-21. Overall, our results advocate for a more nuanced role for CD40L in autoimmunity than has been previously described, particularly in the context of differential cytokine expression and sex, and suggest a boundary threshold of CD40L-CD40 signaling between protection and augmentation of disease.