CD39 expression by regulatory T cells participates in CD8+ T cell suppression during experimental Trypanosoma cruzi infection.

An imbalance between suppressor and effector immune responses may preclude cure in chronic parasitic diseases. In the case of Trypanosoma cruzi infection, specialized regulatory Foxp3+ T (Treg) cells suppress protective type-1 effector responses. Herein, we investigated the kinetics and underlying mechanisms behind the regulation of protective parasite-specific CD8+ T cell immunity during acute T. cruzi infection. Using the DEREG mouse model, we found that Treg cells play a role during the initial stages after T. cruzi infection, restraining the magnitude of CD8+ T cell responses and parasite control. Early Treg cell depletion increased the frequencies of polyfunctional short-lived, effector T cell subsets, without affecting memory precursor cell formation or the expression of activation, exhaustion and functional markers. In addition, Treg cell depletion during early infection minimally affected the antigen-presenting cell response but it boosted CD4+ T cell responses before the development of anti-parasite effector CD8+ T cell immunity. Crucially, the absence of CD39 expression on Treg cells significantly bolstered effector parasite-specific CD8+ T cell responses, preventing increased parasite replication in T. cruzi infected mice adoptively transferred with Treg cells. Our work underscores the crucial role of Treg cells in regulating protective anti-parasite immunity and provides evidence that CD39 expression by Treg cells represents a key immunomodulatory mechanism in this infection model.

The aflatoxin B1 -fumonisin B1 toxicity in BRL-3A hepatocytes is associated to induction of cytochrome P450 activity and arachidonic acid metabolism.

Human oral exposure to aflatoxin B1 (AFB1 ) and fumonisin B1 (FB1 ) is associated with increased hepatocellular carcinoma. Although evidence suggested interactive AFB1 -FB1 hepatotoxicity, the underlying mechanisms remain mostly unidentified. This work was aimed at evaluating the possible AFB1 -FB1 interplay to induce genetic and cell cycle toxicities in BRL-3A rat hepatocytes, reactive oxygen species (ROS) involvement, and the AFB1 metabolizing pathways cytochrome P450 (CYP) and arachidonic acid (ArAc) metabolism as ROS contributors. Flow cytometry of stained BRL-3A hepatocytes was used to study the cell cycle (propidium iodide), ROS intracellular production (DCFH-DA, HE, DAF-2 DA), and phospholipase A activity (staining with bis-BODIPY FL C11-PC). The CYP1A activity was assessed by the 7-ethoxyresorufin-O-deethylase (EROD) assay. Despite a 48-h exposure to FB1 (30 µM) not being genotoxic, the AFB1 (20 µM)-induced micronucleus frequency was overcome by the AFB1 -FB1 mixture (MIX), presumably showing toxin interaction. The mycotoxins blocked G1/S-phase, but only MIX caused cell death. Overall, the oxidative stress led these alterations as the pretreatment with N-acetyl-l-cysteine reduced such toxic effects. While AFB1 had a major input to the MIX pro-oxidant activity, with CYP and ArAc metabolism being ROS contributors, these pathways were not involved in the FB1 -elicited weak oxidative stress. The MIX-induced micronucleus frequency in N-acetyl-l-cysteine pretreated cells was greater than that caused by AFB1 without antioxidants, suggesting enhanced AFB1 direct genotoxicity probably owing to the higher CYP activity and ArAc metabolism found in MIX. The metabolic pathways modulation by AFB1 -FB1 mixtures could raise its hepatocarcinogenic properties.

Effects of aflatoxin B1, fumonisin B1 and their mixture on the aryl hydrocarbon receptor and cytochrome P450 1A induction.

Aflatoxin B1 (AFB1) and fumonisin B1 (FB1) are mycotoxins widely found as cereal contaminants and their co-occurrence in corn has been associated with a high incidence of liver cancer. Both toxins are immunotoxic, with AFB1 being a procarcinogen, and its bioactivation through specific cytochrome P450 (Cyp) enzymes, such as Cyp1A, being a requirement for hepatocarcinogenic and toxic activities. This study evaluated the effects of these mycotoxins, alone or combined, on activation and expression of Cyp1A and its transcription factor aryl hydrocarbon receptor (Ahr) in hepatoma cell line H4IIE and spleen mononuclear cells of rats. The results demonstrate that in H4IIE cells, AFB1 induced an increase in Cyp1A activity and cyp1A transcription, associated with an enhanced Ahr activity, which suggests that this toxin can act as an Ahr agonist. Moreover, FB1 caused a small rise in Cyp1A activity and cyp1A expression. Similarly in spleen cells, AFB1 and FB1 induced overexpression of cyp1A and ahr genes. This work shows that the response potency was significantly higher for the mixture, indicating the existence of an interaction between both toxins. This study proposes the Ahr pathway activation as a toxicity mechanism of AFB1 and FB1, and highlights that FB1 may increase AFB1 bioactivation.

Reactive oxygen species sources and biomolecular oxidative damage induced by aflatoxin B1 and fumonisin B1 in rat spleen mononuclear cells.

Aflatoxin B1 (AFB(1)) and fumonisin B1 (FB(1)) are mycotoxins widely found as cereal contaminants. Their immunotoxicities predispose to infectious diseases and may alter the tumor immunosurveillance of human and animals, but the mechanisms underlying have not been fully elucidated, and the induction of oxidative stress has been proposed as a probable mechanism. This work was aimed at evaluating in spleen mononuclear cells (SMC) from Wistar rats the effects of the exposure, in vitro for up to 48 h, to 20 µM AFB(1), 10 µM FB(1) and AFB(1)-FB(1) mixture (MIX), over cellular oxidative status, as well as at elucidating the contribution of different reactive oxygen species (ROS) to biomolecular oxidative damage, the biochemical pathways involved, and the probable interaction of both toxins to induce oxidative stress. All the treatments increased total ROS and oxidation of biomolecules, with MIX having the greatest effects. However, only MIX increased superoxide anion radical. The main ROS involved in oxidation of proteins, lipids and DNA appear to be hydrogen peroxide and hydroxyl radical. The mitochondrial complex I and CYP450 were involved in the ROS generation induced by all treatments. The NADPH oxidase system was induced by FB1 and MIX. The arachidonic acid metabolism contributed to the ROS formation induced by AFB(1) and MIX. These results demonstrate that an interaction between AFB(1) and FB(1) occur in the oxidative stress induction, and show the biochemical pathways involved in ROS generation in SMC. The oxidative stress could mediate the AFB(1) and FB(1) individual and combined immunotoxicities.