Arsenic trioxide inhibits the response of primary human B cells to influenza virus A in vitro

Arsenic compounds are common environmental toxicants worldwide and particularly enriched in the Northeast and the Southwestern United States, the Alps, and Bangladesh. Exposure to arsenic is linked with various detrimental health outcomes, including cancer, cognitive decline, and kidney damage. Our group has previously shown that arsenic trioxide alters T cell cytokine production. In the current study, we demonstrate that exposure to arsenic compounds alters B cell function in an in vitro influenza model. Human peripheral blood mononuclear cells (PBMCs) were isolated from blood and cultured with arsenic trioxide (As3O2) and subsequently challenged with Influenza A virus. B cells showed decreased expression of CD267, surface IgG and CD80 when treated with As3O2. Taken together, the data suggest that As3O2 affects the activation and surface antibody expression of human peripheral B cells. Overall, this suggests that As3O2 exposure could cause impaired humoral immunity.

Type 1 regulatory T cell-mediated tolerance in health and disease

Type 1 regulatory T (Tr1) cells, in addition to other regulatory cells, contribute to immunological tolerance to prevent autoimmunity and excessive inflammation. Tr1 cells arise in the periphery upon antigen stimulation in the presence of tolerogenic antigen presenting cells and secrete large amounts of the immunosuppressive cytokine IL-10. The protective role of Tr1 cells in autoimmune diseases and inflammatory bowel disease has been well established, and this led to the exploration of this population as a potential cell therapy. On the other hand, the role of Tr1 cells in infectious disease is not well characterized, thus raising concern that these tolerogenic cells may cause general immune suppression which would prevent pathogen clearance. In this review, we summarize current literature surrounding Tr1-mediated tolerance and its role in health and disease settings including autoimmunity, inflammatory bowel disease, and infectious diseases.

BHLHE40 Regulates IL-10 and IFN-γ Production in T Cells but Does Not Interfere With Human Type 1 Regulatory T Cell Differentiation

Type 1 regulatory T (Tr1) cells are subset of peripherally induced antigen-specific regulatory T cells. IL-10 signaling has been shown to be indispensable for polarization and function of Tr1 cells. However, the transcriptional machinery underlying human Tr1 cell differentiation and function is not yet elucidated. To this end, we performed RNA sequencing on ex vivo human CD49b⁺LAG3⁺ Tr1 cells. We identified the transcription factor, BHLHE40, to be highly expressed in Tr1 cells. Even though Tr1 cells characteristically produce high levels of IL-10, we found that BHLHE40 represses IL-10 and increases IFN-γ secretion in naïve CD4⁺ T cells. Through CRISPR/Cas9-mediated knockout, we determined that IL10 significantly increased in the sgBHLHE40-edited cells and BHLHE40 is dispensable for naïve CD4⁺ T cells to differentiate into Tr1 cells in vitro. Interestingly, BHLHE40 overexpression induces the surface expression of CD49b and LAG3, co-expressed surface molecules attributed to Tr1 cells, but promotes IFN-γ production. Our findings uncover a novel mechanism whereby BHLHE40 acts as a regulator of IL-10 and IFN-γ in human CD4⁺ T cells.

The role of Nrf2 in autoimmunity and infectious disease: Therapeutic possibilities

Nrf2 is a cytoprotective transcription factor which is involved in ameliorating oxidative stress and toxic insults. Recently, an immunomodulatory role for Nrf2 has gained appreciation as it has been shown to protect cells and hosts alike in a variety of immune and inflammatory disorders. However, Nrf2 utilizes numerous distinct pathways to elicit its immunomodulatory effects. In this review, we summarize the literature discussing the roles of Nrf2 in autoimmunity and infectious diseases with a goal of understanding the potential to therapeutically target Nrf2.

Identification of a novel mechanism of Th2 polarization in mouse CD4+ T cells through nuclear factor erythroid 2-like 2 (Nrf2) regulation

The nuclear factor erythroid 2-like 2 (Nrf2) transcription factor regulates a battery of detoxification and antioxidant genes following activation by cell stress. The primary role of Nrf2 in immune function was thought to occur as an indirect consequence of oxidative stress. We have previously demonstrated an unknown immunomodulatory role of Nrf2, where activation by the common food preservative, tBHQ, induced Nrf2-dependent skewing of CD4+ T cells towards a Th2 phenotype. Polarization resulted in increased production of Th2 cytokines and DNA binding of the master regulator of Th2 differentiation, GATA3. To date, the molecular mechanism(s) responsible for increased GATA3 activity and subsequent Th2 cytokine protein production are unknown and elucidation of this mechanism(s) is the study objective. Primary mouse CD4+ T cells (WT and Nrf2-null) were treated with tBHQ and GATA3 activity was analyzed. Additionally, Nrf2 binding to putative AREs within an intron and the promoter of the GATA3 gene was investigated in the Th2 clone, D10 cells. Results from these studies show GATA3 gene expression and protein production increased after tBHQ treatment in WT, but not Nrf2-null, mice. In addition, Nrf2 binding to putative AREs in the GATA3 gene was demonstrated in D10 cells by ChIP analysis. The functionality of these putative AREs was established by luciferase assay. Together, results of these experiments suggest that GATA3 is upregulated through a direct mechanism involving Nrf2 at the transcriptional level. Overall, these studies provide strong evidence for the role of Nrf2 in a novel mechanism of Th2 polarization of CD4+ T cells, which could have potential implications in Th2 mediated allergic disorders.

Chronic low-level cadmium exposure in rats affects cytokine production by activated T cells

Cadmium is a toxic metal and common environmental contaminant. Chronic cadmium exposure results in kidney, bone, reproductive, and immune toxicity as well as cancer. Cadmium induces splenomegaly and affects the adaptive immune system, but specific effects vary depending on the dose, model, and endpoint. This study investigates the effects of subchronic, oral, and low-dose cadmium exposure (32 ppm cadmium chloride in drinking water for 10 weeks) on the rat immune system, focusing on T cell function. Cadmium-exposed animals demonstrated slight increases in the spleen-to-body weight ratios, and decreases in overall splenic cell numbers and markers of oxidative stress. The relative ratios of splenic cell populations remained similar, except for modest increases in regulatory T cells in the cadmium-exposed animals. Cadmium exposure also significantly increased the production of IFNγ, a pro-inflammatory cytokine, and IL-10, a cytokine produced by multiple T cell subsets that typically inhibits IFNγ expression, by activated T cells. The increase in IFNγ and IL-10 suggests that cadmium exposure may affect multiple T cell subsets. Collectively, this study suggests that subchronic, low-dose cadmium exposure impacts both immune cell function and cellularity, and may enhance inflammatory responses.

The Nrf2 activator tBHQ inhibits the activation of primary murine natural killer cells

Tert-butylhydroquinone (tBHQ) is a commonly used food preservative with known immunomodulatory activity; however, there is little information regarding its role on natural killer (NK) cell activation and function. tBHQ is a known activator of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which results in induction of cytoprotective genes. Activation of Nrf2 has been shown to modulate immune responses in a number of different models. In addition, studies in our laboratory have shown that tBHQ inhibits numerous early events following T cell activation. In the current study, we investigated whether activated NK cells are impacted by tBHQ, since many signaling cascades that control NK cell effector function also contribute to T cell function. Splenocytes were isolated from female, wild-type C57Bl/6J mice and treated with 1 μM or 5 μM tBHQ. NK cell function was assessed after activation with phorbol 12-myristate 13-acetate (PMA) and ionomycin for 24 h. Activation of NK cells in the presence of tBHQ decreased total NK cell percentage, production of intracellular interferon gamma (IFNɣ), granzyme B, and perforin, and induction of the cell surface proteins CD25 and CD69, which are markers of NK cell activation. In addition to NK cell effector function, NK cell maturation was also altered in response to tBHQ. Notably, this is the first study to demonstrate that the Nrf2 activator, tBHQ, negatively impacts effector function and maturation of NK cells.

Differential effects of the Nrf2 activators tBHQ and CDDO-Im on the early events of T cell activation

We previously demonstrated that activation of the transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2) promotes CD4+ Th2 differentiation. In the current study, we assessed the role of Nrf2 in early events following T cell activation. The Nrf2 activators, tBHQ (tert-butylhydroquinone) and CDDO-Im (the imidazolide derivative of the triterpenoid CDDO), were used in conjunction with splenocytes derived from wild-type and Nrf2-null mice to distinguish between Nrf2-specific and off-target effects. CDDO-Im inhibited early IFNγ production in a largely Nrf2-dependent manner. In contrast, tBHQ and CDDO-Im had little effect on expression of CD25 or CD69. Furthermore, tBHQ inhibited GM-CSF and IL-2 production in both wild-type and Nrf2-null T cells, suggesting this effect is Nrf2-independent. Conversely, CDDO-Im caused a concentration-dependent increase in IL-2 secretion in wild-type, but not Nrf2-null, splenocytes, suggesting that Nrf2 promotes IL-2 production. Interestingly, both compounds inhibit NFκB DNA binding, where the suppression by tBHQ is Nrf2-independent and CDDO-Im is Nrf2-dependent. Surprisingly, as compared to wild-type splenocytes, Nrf2-null splenocytes showed lower nuclear accumulation of c-Jun, a member of the AP-1 family of transcription factors, which have been shown to drive multiple immune genes, including IL-2. Both Nrf2 activators caused a Nrf2-dependent trend toward increased nuclear accumulation of c-Jun. These data suggest that modulation of cytokine secretion by tBHQ likely involves multiple pathways, including AP-1, NFκB, and Nrf2. Overall, the data suggest that Nrf2 activation inhibits secretion of the Th1 cytokine IFNγ, and increases early production of IL-2, which has been shown to promote Th2 differentiation, and may support the later occurrence of Th2 polarization.

Inhibition of early T cell cytokine production by arsenic trioxide occurs independently of Nrf2

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a stress-activated transcription factor that induces a variety of cytoprotective genes. Nrf2 also mediates immunosuppressive effects in multiple inflammatory models. Upon activation, Nrf2 dissociates from its repressor protein, Keap1, and translocates to the nucleus where it induces Nrf2 target genes. The Nrf2-Keap1 interaction is disrupted by the environmental toxicant and chemotherapeutic agent arsenic trioxide (ATO). The purpose of the present study was to determine the effects of ATO on early events of T cell activation and the role of Nrf2 in those effects. The Nrf2 target genes Hmox-1, Nqo-1, and Gclc were all upregulated by ATO (1–2 μM) in splenocytes derived from wild-type, but not Nrf2-null, mice, suggesting that Nrf2 is activated by ATO in splenocytes. ATO also inhibited IFNγ, IL-2, and GM-CSF mRNA and protein production in wild-type splenocytes activated with the T cell activator, anti-CD3/anti-CD28. However, ATO also decreased production of these cytokines in activated splenocytes from Nrf2-null mice, suggesting the inhibition is independent of Nrf2. Interestingly, ATO inhibited TNFα protein secretion, but not mRNA expression, in activated splenocytes suggesting the inhibition is due to post-transcriptional modification. In addition, c-Fos DNA binding was significantly diminished by ATO in wild-type and Nrf2-null splenocytes activated with anti-CD3/anti-CD28, consistent with the observed inhibition of cytokine production by ATO. Collectively, this study suggests that although ATO activates Nrf2 in splenocytes, inhibition of early T cell cytokine production by ATO occurs independently of Nrf2 and may instead be due to impaired AP-1 DNA binding.