Regulatory roles for NKT cell ligands in environmentally induced autoimmunity

Maternal gestational mercury exposure in relation to cord blood T cell alterations and placental gene expression signatures

The immunotoxic impacts of mercury during early life is poorly understood. We investigated the associations between gestational mercury exposure and frequency of cord blood T cells as well as placental gene expression. Frequency of natural Treg cells was positively associated with prenatal and postpartum mercury toenail concentrations. Frequency of NKT and activated naïve Th cells was positively associated with prenatal toenail mercury concentrations and number of maternal silver-mercury dental amalgams, respectively. Placental gene expression analyses revealed distinct gene signatures associated with mercury exposure. Decreased placental expression of a histone demethylase, KDM4DL, was associated with both higher prenatal and postpartum maternal toenail mercury levels among male infants and remained statistically significant after adjustment for fish and seafood consumption. The results suggest that gestational exposure to mercury concentrations contribute to alterations in both T cells and gene expression in placenta at birth. These alterations may inform mechanisms of mercury immunotoxicity.

Oral dysbiosis induced by Porphyromonas gingivalis is strain-dependent in mice

Background:Porphyromonas gingivalis strain W83, one of the most widely investigated, is considered virulent in the context of periodontitis. The recently isolated P. gingivalis TDC60 has been reported to be highly pathogenic, although it has not yet been investigated in a mouse periodontitis model by oral gavage.

Aim: Our aim was to compare the virulence of both strains by evaluating their impact on alveolar bone loss and the composition of oral microbiota.

Methods: We inoculated by oral gavage C57BL/6 mice with either one of the two P. gingivalis strains and compared to a sham-treated group, without antibiotics pre-treatment. The mandibular alveolar bone of treated mice and controls were assessed, one month after the final inoculation, by microCT measurements. Moreover, at this time, we characterized their oral microbiota by 16S rRNA gene sequencing.

Results: While P. gingivalis W83 successfully initiated periodontitis, TDC60-treated mice only experienced moderate lesions. Furthermore, only W83-treated mice exhibited a specific distinct microbiota, with significantly lower richness and evenness than other samples, and decreased proportions of taxa usually found in healthy individuals.

Conclusion: This association between alveolar bone loss and a major persistent shift of the oral microbiota gives insights into virulence discrepancies among these bacterial strains.

From the Cover: Interplay Between IFN-γ and IL-6 Impacts the Inflammatory Response and Expression of Interferon-Regulated Genes in Environmental-Induced Autoimmunity

IFN-γ has been found to be robustly important to disease pathogenesis in both idiopathic and induced models of murine lupus. In transgenic mice, over production of IFN-γ in the skin results in an inflammatory response and autoimmunity. This suggests that localized exposure to environmental factors that induce autoimmunity may be associated with expression of an IFN-γ-dependent inflammatory response. Using murine mercury-induced autoimmunity (mHgIA), the severity of inflammation and proinflammatory cytokine expression, including the cellular source of IFN-γ, were assessed at the site of subcutaneous exposure and in secondary lymphoid organs. Exposure induced a localized chronic inflammation comprising both innate and adaptive immune cells but only CD8+ T and NK cells were reduced in the absence of IFN-γ. IFN-γ+ cells began to appear as early as day 1 and comprised both resident (γδ T) and infiltrating cells (CD8+ T, NKT, CD11c+). The requirements for inflammation were examined in mice deficient in genes required (Ifng, Il6) or not required (Casp1) for mHgIA. None of these genes were essential for induction of inflammation, however IFN-γ and IL-6 were required for exacerbation of other proinflammatory cytokines. Additionally, lack of IFN-γ or IL-6 impacted expression of genes regulated by either IFN-γ or type I IFN. Significantly, both IFN-γ and IL-6 were required for increased expression of IRF-1 which regulates IFN stimulated genes and is required for mHgIA. Thus IRF-1 may be at the nexus of the interplay between IFN-γ and IL-6 in exacerbating a xenobiotic-induced inflammatory response, regulation of interferon responsive genes and autoimmunity.

Inhibitory effect of antidepressant drugs on contact hypersensitivity reaction is connected with their suppressive effect on NKT and CD8(+) T cells but not on TCR delta T cells

BACKGROUND

Contact hypersensitivity (CHS) reaction induced by a topical application of hapten is a cell-mediated antigen-specific type of skin inflammation mediated by interaction of several subtypes of T cell subpopulations. Recently, it has been shown that antidepressant drugs inhibit CHS reaction, although the mechanism of this effect remains unknown. The aim of the present study was to investigate the effect of 2-week desipramine or fluoxetine administration on the CHS reaction induced by picryl chloride (PCL) application in B10.PL mice and in knock-out mice established on B10.PL background: TCRδ(-/-) mice lacking TCRγδ T lymphocytes; β2m(-/-) mice lacking CD8(+) T lymphocytes and CD1d(-/-) mice lacking CD1d dependent natural killer T (NKT) lymphocytes.

METHODS

B10.PL, TCRδ(-/-), β2m(-/-) and CD1d(-/-) mice were divided into six groups: 1) vehicle-treated negative control group; 2) desipramine-treated negative control group; 3) fluoxetine-treated negative control group; 4) vehicle and PCL-treated group (positive control group); 5) desipramine and PCL-treated group; and 6) fluoxetine and PCL-treated group. CHS to PCL was tested by evaluation of ear swelling. Metabolic activity of spleen and lymph node cells were estimated by MTT test.

RESULTS

The antidepressants significantly suppressed the CHS reaction in B10.PL mice: desipramine by 55% and fluoxetine by 42% compared to the positive control. This effect was even stronger in TCRδ(-/-) mice, in which fluoxetine reduced the ear swelling by 73% in comparison with the vehicle-treated positive control group. On the other hand, desipramine and fluoxetine did not inhibit CHS reaction in β2m(-/-) and CD1d(-/-) mice. Moreover, PCL increased metabolic and/or proliferative activity of splenocytes in all four strains of mice whereas the antidepressants decreased this activity of splenocytes in B10.PL, TCRδ(-/-) and CD1d(-/-) mice.

CONCLUSION

The results of the present study show that lack of CD8(+) T cells or NKT cells abolishes the immunosuppressive effect of antidepressant drugs on PCL-induced CHS reaction in mice. These results suggest that antidepressant drug-induced inhibition of CHS reaction is connected with their inhibitory effect on ability of CD8(+) T cells and NKT cells to induce and/or escalate CHS reaction. TCRγδ cells seem not to be involved in antidepressant-induced suppression of CHS.

Cathepsin B regulates the appearance and severity of mercury-induced inflammation and autoimmunity

Susceptibility and resistance to systemic autoimmunity are genetically regulated. This is particularly true for murine mercury-induced autoimmunity (mHgIA) where DBA/2J mice are considered resistant to disease including polyclonal B cell activation, autoantibody responses, and immune complex deposits. To identify possible mechanisms for the resistance to mHgIA, we exposed mHgIA sensitive B10.S and resistant DBA/2J mice to HgCl2 and assessed inflammation and pro-inflammatory responses at the site of exposure and subsequent development of markers of systemic autoimmunity. DBA/2J mice showed little evidence of induration at the site of exposure, expression of proinflammatory cytokines, T cell activation, or autoantibody production, although they did exhibit increased levels of total serum IgG and IgG1. In contrast B10.S mice developed significant inflammation together with increased expression of inflammasome component NLRP3, proinflammatory cytokines IL-1β, TNF-α, and IFN-γ, hypergammaglobulinemia, splenomegaly, CD4(+) T-cell activation, and production of autoantibodies. Inflammation in B10.S mice was associated with a selective increase in activity of cysteine cathepsin B but not cathepsins L or S. Increased cathepsin B activity was not dependent on cytokines required for mHgIA but treatment with CA-074, a cathepsin B inhibitor, led to transient reduction of local induration, expression of inflammatory cytokines, and subsequent attenuation of the systemic adaptive immune response. These findings demonstrate that sensitivity to mHgIA is linked to an early cathepsin B regulated inflammatory response which can be pharmacologically exploited to abrogate the subsequent adaptive autoimmune response which leads to disease.

Lymphocyte Activation Gene-3 (LAG-3) negatively regulates environmentally-induced autoimmunity

Environmental factors including drugs, mineral oils and heavy metals such as lead, gold and mercury are triggers of autoimmune diseases in animal models or even in occupationally exposed humans. After exposure to subtoxic levels of mercury (Hg), genetically susceptible strains of mice develop an autoimmune disease characterized by the production of highly specific anti-nucleolar autoantibodies, hyperglobulinemia and nephritis. However, mice can be tolerized to the disease by a single low dose administration of Hg. Lymphocyte Activation Gene-3 (LAG-3) is a CD4-related, MHC-class II binding molecule expressed on activated T cells and NK cells which maintains lymphocyte homeostatic balance via various inhibitory mechanisms. In our model, administration of anti-LAG-3 monoclonal antibody broke tolerance to Hg resulting in autoantibody production and an increase in serum IgE level. In addition, LAG-3-deficient B6.SJL mice not only had increased susceptibility to Hg-induced autoimmunity but were also unresponsive to tolerance induction. Conversely, adoptive transfer of wild-type CD4⁺ T cells was able to partially rescue LAG-3-deficient mice from the autoimmune disease. Further, in LAG-3-deficient mice, mercury elicited higher amounts of IL-6, IL-4 and IFN-γ, cytokines known to play a critical role in mercury-induced autoimmunity. Therefore, we conclude that LAG-3 exerts an important regulatory effect on autoimmunity elicited by a common environmental pollutant.

The role of decay accelerating factor in environmentally induced and idiopathic systemic autoimmune disease

Decay accelerating factor (DAF) plays a complex role in the immune system through complement-dependent and -independent regulation of innate and adaptive immunity. Over the past five years there has been accumulating evidence for a significant role of DAF in negatively regulating adaptive T-cell responses and autoimmunity in both humans and experimental models. This review discusses the relationship between DAF and the complement system and highlights major advances in our understanding of the biology of DAF in human disease, particularly systemic lupus erythematosus. The role of DAF in regulation of idiopathic and environmentally induced systemic autoimmunity is discussed including studies showing that reduction or absence of DAF is associated with autoimmunity. In contrast, DAF-mediated T cell activation leads to cytokine expression consistent with T regulatory cells. This is supported by studies showing that interaction between DAF and its molecular partner, CD97, modifies expression of autoimmunity promoting cytokines. These observations are used to develop a hypothetical model to explain how DAF expression may impact T cell differentiation via interaction with CD97 leading to T regulatory cells, increased production of IL-10, and immune tolerance.

β2-microglobulin is required for the full expression of xenobiotic-induced systemic autoimmunity

Mercury exposure in both humans and mice is associated with features of systemic autoimmunity. Murine HgCl₂-induced autoimmunity (mHgIA) requires MHC Class II, CD4⁺ T-cells, co-stimulatory molecules, and interferon-γ (IFN-γ), similar to spontaneous models of systemic lupus erythematosus (SLE). β₂-microglobulin (B2m) is required for functional MHC Class I molecules and the neonatal F(c) receptor (F(c)Rn). Deficiency of B2m in lupus-prone strains is consistently associated with reduced IgG levels, but with variable effects on other manifestations. Herein, we examined the role of B2m in mHgIA and show that in the absence of B2m, mercury-exposed mice failed to exhibit hypergammaglobulinemia, had reduced anti-nucleolar autoantibodies (ANoA), and had a lower incidence of immune complex deposits in splenic blood vessels, whereas IgG anti-chromatin autoantibodies and renal immune deposits were largely unaffected. Subclass analysis of the IgG anti-chromatin, however, revealed a significant reduction in the IgG₁ subtype. Examination of IFNγ, IL-4, and IL-2 in exposed skin, draining lymph nodes, and spleen following mercury exposure showed reduced IL-4 in the spleen and skin in B2m-deficient mice, consistent with the lower IgG₁ anti-chromatin levels, and reduced IFNγ expression in the skin. These findings demonstrate how a single genetic alteration can partially but significantly modify the clinical manifestations of systemic autoimmunity induced by exposure to xenobiotics.

Invariant NK T cells: potential for immunotherapeutic targeting with glycolipid antigens

Invariant NK T (iNKT) cells are a subset of T lymphocytes that recognize glycolipid antigens bound with the antigen-presenting molecule CD1d. iNKT cells have potent immunoregulatory activities that can promote or suppress immune responses during different pathological conditions. These immunoregulatory properties can be harnessed for therapeutic purposes with cognate glycolipid antigens, such as the marine sponge-derived glycosphingolipid α-galactosylceramide. Preclinical studies have shown substantial promise for iNKT cell-based treatments of infections, cancer and autoimmune and inflammatory diseases. Translation of these preclinical studies to the clinic, while faced with some obstacles, has already had some initial success. In this article, we review the immunodulatory activities of iNKT cells and the potential for developing iNKT cell-based prophylactic and curative therapies of human disease.

Risk of autoimmune disease: challenges for immunotoxicity testing

Autoimmunity represents a potentially diverse and complex category among the range of adverse outcomes for detection with immunotoxicity testing. For this reason, the risk of autoimmune disease is discussed in this overview chapter with additional mention among the later specific protocol chapters. Improvements in clinical diagnostic capabilities and disease recognition have led to a more accurate picture of the extent of autoimmune diseases across different human populations. While the risk of any single autoimmune disease remains modest when compared with that of lung or heart disease, the cumulative prevalence of autoimmune diseases is both significant and increasing. Autoimmune diseases are usually viewed in the context of the damaged tissue or organ (e.g., as a thyroid, gastrointestinal, cardiovascular or neurological disease). But improved recognition that underlying immune dysfunction can connect the risks for these as well as other diseases is critical for optimizing risk assessment. Since autoimmune diseases are chronic in nature with many first appearing in children or in young adults, these diseases exert a serious impact on both health care costs and quality of life. This chapter provides a discussion of the issues that should be considered with immunotoxicity testing for risk of autoimmunity.

Application of tissue-specific NK and NKT cell activity for tumor immunotherapy

Natural killer (NK) and NKT cells are a first line of defense against pathogens and transformed cells. However, dysregulation of their function can lead to autoimmune disease. A better understanding of the mechanisms controlling NK and NKT effector function should lead to the development of improved strategies for the treatment of many diseases. The site in which NK and NKT cells reside should be taken into account, because accumulating evidence suggests that the tissue microenvironment strongly influences their function. In this regard, the liver represents a unique immunologic organ in which the balance between the need for tolerance and the ability to respond rapidly to pathogens and tissue injury is tightly regulated. NK cells in the liver have augmented cytolytic activity as compared to other organs, which is consistent with a role for liver-associated NK cells in being critical effector cells for inhibiting tumor metastasis in the liver. Several studies also suggest that hepatic NKT cells have different functions than those in other organs. Whereas splenic and thymic NKT cells have been shown to suppress diabetes development, facilitate the induction of systemic tolerance and are regulated by IL-4 and other Th2 cytokines, certain subsets of NKT cells in the liver are important sources of Th1 cytokines such as Interferon gamma, and are the primary mediators of anti-tumor responses. The unique properties and roles as critical effector cells make NK and NKT cells within the liver microenvironment attractive targets of immunotherapeutic approaches that have the goal of controlling tumor metastasis in the liver.