Mechanistic Insights on The Immunomodulatory Functions of Diverse Environmental Factors on Systemic Autoimmunity

Abstract

The immune defense is geared to protect against a tremendous array of invaders. The ultimate goal of the immune system is to induce effective and balanced inflammatory responses that enable the efficient elimination of possible threats while avoiding both immunodeficiency and autoimmunity. The skewness towards inflammatory responses causing excessive collateral damage could lead to diverse autoimmune conditions. These conditions could be organ-specific or result from systemic immune dysregulations called systemic autoimmunity. The multifaceted nature and the intricate clinical heterogeneity of systemic autoimmune conditions indicate a strong influence of environmental factors on their immunopathogenesis, where environmental factors could either hinder or contribute to autoimmune development. We focused our research on deciphering the complex effects of environmental factors on the immunopathogenesis of systemic immune dysregulation, taking systemic lupus erythematosus (SLE or Lupus) as a model of systemic autoimmunity. SLE is one of the most mysterious autoimmune disorders with no known cure. In SLE, breaching of tolerance to self-antigens and the subsequent persistent inflammation and collateral tissue damage in multiple organs lead to very diverse clinical manifestations. These manifestations are a result from the interplay between multiple genetic susceptibilities and diverse environmental factors. To date, management plans for SLE are based on non-selective immunosuppressants that could impose significant side effects including increased risks of infection and infection-related mortalities. In parallel, environmental factors and the quality of life could significantly impact SLE management strategies. Therefore, delineating the immunomodulatory capacities of environmental factors would likely unravel more effective management strategies for SLE patients. The current research aims to investigate the central hypothesis that dietary and hygienic components modulate the immune dysregulations of SLE in a tissue- and disease stage-specific manner. We have focused on uncovering the complex effects of Vitamin A (VA) as an essential micronutrient with very diverse immunomodulatory capacities, and quaternary ammonium compound (QAC)-based disinfectants as ubiquitously used disinfectants that have been linked to immunotoxicity, on the immunopathogenesis of SLE. Due to the strong female bias of SLE where women especially of childbearing age are more prone to lupus, we have focused our research on delineating how these diverse factors shape the immunopathogenesis of SLE in female mice only. The first project dissected the immunomodulatory effects of VA, a potent immunomodulatory dietary component. Notably, VA exerts its function through a predominant metabolite known as all-trans-retinoic acid (tRA) that, as we have previously shown, has paradoxical and tissue-specific implications on lupus inflammation. Here, we utilized a pristane-induced model of lupus to investigate the disease stage-dependent effects of tRA. Oral supplementation of tRA was given either before pristane induction of lupus from weaning (3 weeks) to 3 months of age or after pristane induction of lupus from 3 to 9 months of age. We found that tRA treatment mediated disease stage-dependent effects and differentially affected the lupus-associated kidney inflammation (lupus nephritis) when given at the initiation vs. continuation phase of lupus. Unlike tRA treatment during active disease, pre-pristane treatment with tRA aggravated glomerulonephritis through potentiating leukocyte activation and trafficking to the kidney and augmenting renal pro-fibrotic signals. Post-pristane tRA treatment, on the other hand, exerted immunosuppressive functions of decreasing circulatory and renal deposition of autoantibodies as well as suppressing the renal expression of proinflammatory cytokines and chemokines. Interestingly, both pre- and post-pristane treatments with tRA reversed the pristane-induced leaky gut and similarly modulated the gut microbiota, suggesting a gut microbiota-independent mechanism by which tRA affects the initiation vs. continuation phase of lupus. As tRA could be protective against lupus nephritis especially during the active disease stage, and previous reports had shown hypovitaminosis A (reduced serum retinol levels) proceeding SLE, we expanded our investigation to decipher whether VA deficiency (VAD) was a contributing factor for severe SLE and to delineate how VAD affected the initiation and/or the progression of lupus nephritis in genetically-prone conditions. For that purpose, we utilized the classical murine lupus-prone model, MRL/lpr, and initiated VAD either during the gestation or after weaning to reveal potential time-dependent effects. VAD exacerbated lupus nephritis by provoking severe neutrophilic tubulointerstitial nephritis, and accelerated renal failure. This was concomitant with significantly higher mortality in all VAD mice. Mechanistically, VAD enhanced early activation of plasma cells and augmented their autoantibodies production. In addition, VAD led to an enhanced expansion of pathogenic T lymphocytes. In parallel, VAD increased renal infiltration of conventional and plasmacytoid dendritic cells. Our findings establish VAD as a driving factor for lupus nephritis progression in genetically predisposed conditions. These findings emphasize the importance of monitoring VA levels in SLE patients and urge for VA supplementations for patients at higher risk for hypovitaminosis A, especially during the maternal-neonatal interface. Additionally, this project warrants further investigations to delineate the molecular targets through which VA modulates cellular functions as well as immunopathogenesis of lupus nephritis. The information obtained from these studies may also benefit women with other autoimmune conditions and will pave the way for VA supplementations to be tested in clinical trials. The second project investigated the effects of ambient exposure to QAC-based disinfectants on the progression of murine SLE in genetically prone mice. We compared the disease progression in MRL/Lpr mice that have been exposed to QACs vs. those kept under a complete QAC-free condition. QAC-based disinfectants CP-64 or Labsan 256 were used under QAC-exposed conditions, while ethanol was used in the QAC-free environment. We found that compared to QAC-free mice, ambient exposure of lupus-prone mice to QACs led to smaller spleens with no change in circulating autoantibodies or the severity of glomerulonephritis. This suggests that QACs may have immunosuppressive effects on lupus. Using a microfluidic device, we showed that ambient exposure to QACs reduced directional migration of bone marrow-derived neutrophils toward an inflammatory chemoattractant ex vivo. Consistent with this, we found decreased infiltration of neutrophils into the spleen. While bone marrow-derived neutrophils appeared to exhibit a pro-inflammatory profile, upregulated expression of PD-L1 was observed on neutrophils that infiltrated the spleen, which in turn interacted with PD-1 on T cells and modulated their fate. Specifically, QAC exposure hindered activation of splenic T cells and increased apoptosis of effector T-cell populations. Collectively, these results suggest that ambient QAC exposure decreases lupus-associated splenomegaly likely through neutrophil-mediated toning of T-cell activation and/or apoptosis. However, our findings also indicate that even ambient exposure could alter immune cell phenotypes, functions, and their fate. Further investigations on how QACs affect immunity under steady-state conditions are warranted. Collectively, the findings of this doctoral research suggest temporal and spatial effects of diet and hygiene on systemic autoimmunity and emphasize the strong influence of environmental factors toning cellular immune responses and subsequently shaping autoimmune outcomes. Our findings could pave the way for more personalized healthcare plans for autoimmune patients that take into consideration tissue involvement, disease stages, and the patient's lifestyle.