Limited Effect of Indolamine 2,3-Dioxygenase Expression and Enzymatic Activity on Lupus-Like Disease in B6.Nba2 Mice

Regulation of macrophage polarization by targeted metabolic reprogramming for the treatment of lupus nephritis

Lupus nephritis (LN) is a severe and common manifestation of systemic lupus erythematosus (SLE) that is frequently identified with a poor prognosis. Macrophages play an important role in its pathogenesis. Different macrophage subtypes have different effects on lupus-affected kidneys. Based on their origin, macrophages can be divided into monocyte-derived macrophages (MoMacs) and tissue-resident macrophages (TrMacs). During nephritis, TrMacs develop a hybrid pro-inflammatory and anti-inflammatory functional phenotype, as they do not secrete arginase or nitric oxide (NO) when stimulated by cytokines. The infiltration of these mixed-phenotype macrophages is related to the continuous damage caused by immune complexes and exposure to circulating inflammatory mediators, which is an indication of the failure to resolve inflammation. On the other hand, MoMacs differentiate into M1 or M2 cells under cytokine stimulation. M1 macrophages are pro-inflammatory and secrete pro-inflammatory cytokines, while the M2 main phenotype is essentially anti-inflammatory and promotes tissue repair. Conversely, MoMacs undergo differentiation into M1 or M2 cells in response to cytokine stimulation. M1 macrophages are considered pro-inflammatory cells and secrete pro-inflammatory mediators, whereas the M2 main phenotype is primarily anti-inflammatory and promotes tissue repair. Moreover, based on cytokine expression, M2 macrophages can be further divided into M2a, M2b, and M2c phenotypes. M2a and M2c have anti-inflammatory effects and participate in tissue repair, while M2b cells have immunoregulatory and pro-inflammatory properties. Further, memory macrophages also have a role in the advancement of LN. Studies have demonstrated that the polarization of macrophages is controlled by multiple metabolic pathways, such as glycolysis, the pentose phosphate pathway, fatty acid oxidation, sphingolipid metabolism, the tricarboxylic acid cycle, and arginine metabolism. The changes in these metabolic pathways can be regulated by substances such as fish oil, polyenylphosphatidylcholine, taurine, fumaric acid, metformin, and salbutamol, which inhibit M1 polarization of macrophages and promote M2 polarization, thereby alleviating LN.

Effectiveness of Soluble CTLA-4-Fc in the Inhibition of Bone Marrow T-Cell Activation in Context of Indoleamine 2.3-Dioxygenase (IDO) and CD4+Foxp3+ Treg Induction

Background

Rheumatoid arthritis (RA) is a chronic autoimmune disease with systemic inflammation finally resulting in damaged joints. One of the RA development models suggests bone marrow (BM) as a place of inflammation development further leading to disease progression. We aimed to investigate the potential of CTLA-4-Fc molecule in inducing tolerogenic milieu in BM measured as indoleamine 2,3-dioxygenase (IDO) expression, CD4⁺Foxp3⁺ Treg induction, and T cell activation control. The expression of IDO-pathway genes was also examined in monocytes to estimate the tolerogenic potential in the periphery.

Methods

Bone marrow mononuclear cells (BMMC) were stimulated by pro-inflammatory cytokines and CTLA-4-Fc. Next IDO expression, CD4⁺CD69⁺ and CD4⁺Foxp3⁺ percentage were estimated by PCR and FACS staining, respectively. Enzymatic activity of IDO was confirmed by HPLC in BM plasma and blood plasma. Genes expressed in IDO-pathway were analyzed by NGS in peripheral monocytes isolated from RA patients and healthy controls.

Results

We found that CTLA-4-Fc and IFN-γ stimulation results in IDO production by BMMC. CTLA-4-Fc induced tryptophan catabolism can inhibit mitogen-induced CD4⁺ T cells activation without influencing CD8⁺ cells, but did not control CD25 nor Foxp3 expression in BM cells. Significantly higher expression of selected IDO-pathway genes was detected on peripheral monocytes isolated from RA as compared to healthy controls.

Conclusion

This study sheds light on some immunosuppression aspects present or induced in BM. The potential of IDO-mediated pathways were confirmed in the periphery, what may represent the promising candidates for therapeutic strategies in RA.

Impact of IDO1 and IDO2 on the B Cell Immune Response

Indoleamine-2,3-dioxygenase (IDO)1 and IDO2 are closely related tryptophan catabolizing enzymes that have immunomodulatory properties. Although initially studied as modifiers of T cell activity, emerging evidence suggests IDO1 and IDO2 also have important roles as modulators of B cell function. In this context, IDO1 and IDO2 appear to play opposite roles, with IDO1 inhibiting and IDO2 driving inflammatory B cell responses. In this mini review, we discuss the evidence for IDO1 and IDO2 modulation of B cell function, focusing on the effect of these enzymes on autoimmunity, allergic responses, protective immunity, and response to pathogens. We summarize strategies to target IDO1 and/or IDO2 as potential therapeutics for inflammatory autoimmune disease and highlight outstanding questions and areas that require future study.

Exploration of Potential Integrated Models of N6-Methyladenosine Immunity in Systemic Lupus Erythematosus by Bioinformatic Analyses

Systemic lupus erythematosus (SLE) is a prototypical systemic autoimmune disease of unknown etiology. The epigenetic regulation of N6-methyladenosine (m6A) modification in immunity is emerging. However, few studies have focused on SLE and m6A immune regulation. In this study, we aimed to explore a potential integrated model of m6A immunity in SLE. The models were constructed based on RNA-seq data of SLE. A consensus clustering algorithm was applied to reveal the m6A-immune signature using principal component analysis (PCA). Univariate and multivariate Cox regression analyses and Kaplan–Meier analysis were used to evaluate diagnostic differences between groups. The effects of m6A immune-related characteristics were investigated, including risk evaluation of m6A immune phenotype-related characteristics, immune cell infiltration profiles, diagnostic value, and enrichment pathways. CIBERSORT, ESTIMATE, and single-sample gene set enrichment analysis (ssGSEA) were used to evaluate the relative immune cell infiltrations (ICIs) of the samples. Conventional bioinformatics methods were used to identify key m6A regulators, pathways, gene modules, and the coexpression network of SLE. In summary, our study revealed that IGFBP3 (as a key m6A regulator) and two pivotal immune genes (CD14 and IDO1) may aid in the diagnosis and treatment of SLE. The potential integrated models of m6A immunity that we developed could guide clinical management and may contribute to the development of personalized immunotherapy strategies.

Differential Roles of IDO1 and IDO2 in T and B Cell Inflammatory Immune Responses

Indoleamine-2,3-dioxygenase (IDO)1 and IDO2 are two closely related tryptophan catabolizing enzymes encoded by linked genes. The IDO pathway is also immunomodulatory, with IDO1 well-characterized as a mediator of tumor immune evasion. Due to its homology with IDO1, IDO2 has been proposed to have a similar immunoregulatory function. Indeed, IDO2, like IDO1, is necessary for the differentiation of regulatory T cells in vitro. However, compared to IDO1, in vivo studies demonstrated a contrasting role for IDO2, with experiments in preclinical models of autoimmune arthritis establishing a proinflammatory role for IDO2 in mediating B and T cell activation driving autoimmune disease. Given their potentially opposing roles in inflammatory responses, interpretation of results obtained using IDO1 or IDO2 single knockout mice could be complicated by the expression of the other enzyme. Here we use IDO1 and IDO2 single and double knockout (dko) mice to define the differential roles of IDO1 and IDO2 in B cell-mediated immune responses. Autoreactive T and B cell responses and severity of joint inflammation were decreased in IDO2 ko, but not IDO1 ko arthritic mice. Dko mice had a reduction in the number of autoantibody secreting cells and severity of arthritis: however, percentages of differentiated T cells and their associated cytokines were not reduced compared to IDO1 ko or wild-type mice. These data suggest that autoreactive B cell responses are mediated by IDO2, while autoreactive T cell responses are indirectly affected by IDO1 expression in the IDO2 ko mice. IDO2 also influenced antibody responses in models of influenza infection and immunization with T cell-independent type II antigens. Taken together, these studies provide evidence for the contrasting roles IDO1 and IDO2 play in immune responses, with IDO1 mediating T cell suppressive effects and IDO2 working directly in B cells as a proinflammatory mediator of B cell responses.