Despite advances in our understanding host immune responses to Trypanosoma cruzi, Chagas disease affects an estimated 7 million people globally and continues to pose a substantial public health concern. Gonadal hormones, such as testosterone (TS), are known to modulate immunity and may affect the severity of infections, including those caused by T. cruzi. In this study, we investigated the effects of testosterone on acute experimental T. cruzi infection in male Wistar Hannover rats. Animals were placed into four groups: orchiectomized (OCX), infected, testosterone supplemented, and control. Testosterone did not affect peripheral parasitemia, but it did increase the number of amastigote nests in heart tissue, reducing circulating leukocytes and neutrophils. In the liver, testosterone insufficiency was linked to increased local inflammation, including IL-6, IL-17, MPO, and NAG activity, whereas testosterone supplementation raised IL-10 levels. In the thymus, testosterone increased thymocyte death and impaired T cell development. While testosterone enhanced the frequency of CD4+FOXp3+ regulatory T cells in the spleen, androgen deprivation promoted the development of memory T cell subpopulations and the activation of macrophages and dendritic cells. Taken together, these results show that testosterone suppresses the immune system during T. cruzi infection by reducing the activation of important immune cells without directly influencing blood parasitemia. In contrast, androgen deprivation promotes a more active immune response, suggesting that the host's hormonal state plays a critical role in immune regulation during the acute phase of Chagas disease.

Despite all the scientific progress in recent decades to unravel the immune processes and the way the parasite bypasses the immune system, Chagas disease is still a major public health problem, affecting an estimated 3.5 million people. Among the components that may participate in the response against the parasite, testosterone has been gaining more and more visibility. Studies indicate that the parasite itself seems to carry out steroidogenesis, in which, in co-culture with androgen precursors, T. cruzi has been shown to produce TS, but the purpose of the TS synthesized by the parasite and how this can influence its invasion glycoproteins is still unclear unknown. The aim of this study was to evaluate the influence of testosterone in Trypanosoma cruzi infection on the immune response of bone marrow-derived macrophages. Bone marrow from male rats was extracted and cultured with RMPI medium containing 30% L929 cell supernatant for macrophage differentiation. The cells were incubated for 10 days and, after this period, they were seeded in 96 wells in the amount of 1 x 105 cells per well. TS was added at different concentrations of 20 μM, 10 μM, 5 μM and 1 μM and then infected with the Y strain of T. cruzi, at a rate of 10 parasites per cell, with the culture remaining for six, 12 and 24 h. The supernatant was collected and the production of nitric oxide (NO), tumor necrosis factor (TNF) and the number of cell parasites was assessed by staining with 4'-6'-diamino-2-phenylindole (DAPI) and ranked by high Content Screening (HSC). The parasite was then cultured with the addition of TS, at the mentioned concentrations, leaving it for six and 12 h and then performing the RT-PCR of the mucins. DAPI staining revealed a significant increase in the number of parasites in cells containing TS. The exception was observed when 1 μM of hormone/well was used. A reduction in TNF production was found with 20 and 10 μM of TS for 6 h stimulation, although increased levels were observed with 5 and 1 μM, similar to the infected control. However, there was an increase in TNF production and not after 12 h. The relative expression of parasite glycoprotein 82 was increased with the presence of TS in the medium, regardless of time. Our data suggest that TS may contribute to cellular immunosuppression, increasing parasite infection in the cell, as well as inflammatory mediators that lead to cell and tissue damage in infected individuals, as well as the possible use of TS to allow their invasion into the cell hosts.

Background: Obesity is a global problem associated with several conditions, including hypertension, diabetes, arthritis and cardiovascular diseases. With the increase in the prevalence of obesity in recent years, mostly in developing countries, it is important to study its impact on various diseases, including infectious illnesses, such as Chagas disease, caused by the protozoan Trypanosoma cruzi. Considering that a diet rich in salt, sugar, and fat is associated with obesity, this study aimed to evaluate the influence of cafeteria diet (CAF)-induced obesity on immune responses in T. cruzi-infected rats.Methods: Male Wistar Hannover rats were provided with water and food ad libitum (chow group). The CAF-fed groups received a normal rodent diet or CAF. The animals were intraperitoneally infected with 10(5) trypomastigote forms of the Y strain of T. cruzi present in the whole blood from a previously infected mouse.Results: CAF-fed rats showed a significant increase in visceral adipose tissue weight compared to chow-fed rats. A significant reduction in CD3(+) CD4(+) helper splenic T cells was observed in obese-infected rats compared to non-obese-infected rats, as well as CD11b and macrophages. In addition, macrophages from obese animals displayed reduced RT1b levels compared to those from control animals. Moreover, INF-gamma, an important factor in macro-phage activation, was reduced in obese-infected rats compared with their counterparts.Conclusions: These results indicate that a CAF can impair the cell-mediated immune response against T. cruzi.

Dysbiosis and disturbances in gut homeostasis may result in dysregulated responses, which are common in inflammatory bowel diseases (IBD). These conditions may be refractory to the usual treatments and novel therapies are still necessary to reach a more successful regulation of intestinal immunity. The hormone melatonin (MLT) has been raised as a therapeutic alternative because of its known interactions with immune responses and gut microbiota. Hence, we evaluated the effects of MLT in experimental colitis that evolves with intestinal dysbiosis, inflammation and bacterial translocation. C57BL/6 mice were exposed to dextran sulfate sodium and treated with MLT. In acute colitis, the hormone led to increased clinical, systemic and intestinal inflammatory parameters. During remission, continued MLT administration delayed recovery, increased TNF, memory effector lymphocytes and diminished spleen regulatory cells. MLT treatment reduced Bacteroidetes and augmented Actinobacteria and Verrucomicrobia phyla in mice feces. Microbiota depletion resulted in a remarkable reversion of the colitis phenotype after MLT administration, including a counter-regulatory immune response, reduction in TNF and colon macrophages. There was a decrease in Actinobacteria, Firmicutes and, most strikingly, Verrucomicrobia phylum in recovering mice. Finally, these results pointed to a gut-microbiota-dependent effect of MLT in the potentiation of intestinal inflammation.

Oxidative stress with higher levels of leptin and inflammatory response are key processes related to pathogenesis of both T. cruzi infection and aging. Nuclear factor erythroid 2-related factor 2 (Nrf2) controls the expression of several genes implicated in the oxidative stress response in many pathological conditions. Melatonin is a pleiotropic hormone with, antioxidant, anti-inflammatory and anti-aging actions. Then, we hypothesized that Nrf2 response is impaired during the acute T. cruzi (9 days) infection and that melatonin rescues Nrf2 responses. Young (5 weeks-old) and middle-aged (18 months-old) male Wistar rats were infected with T. cruzi. Nrf2 translocation and markers of inflammation and oxidative stress were analyzed in blood and spleen. Increased apoptosis levels and oxidative stress indicators were observed in the rat spleen during T. cruzi infection. These responses were accompanied by decreased Nrf2 expression and increased expression of nuclear factor kappa B (NF kappa B). Melatonin (5 mg/kg/day; p.o. gavage) attenuated the superoxide anion (O-2(-center dot)) and hydrogen peroxide (H2O2) production induced by T. cruzi infection. Increased expressions of catalase and superoxide dismutase (SOD) were detected in the spleen of melatonin-treated rats infected with T. cruzi. Melatonin treatment inhibited the spleen NF-kappa B activation and downregulates the levels of circulating interleukin (IL)-4, IL-10 and tumor necrosis factor (TNF)-alpha in T. cruzi middle-aged infected rats. Increased levels of the chemokine CXCL1 in middle-aged control rats was observed, confirming that aging alters the production of this chemokine. In T. cruzi infected young animals, CXCL1 was up-regulated when compared to non-infected young ones. For young or middle-aged animals, melatonin treatment had no significant effect on CXCL1 levels. Our findings demonstrate an important role for Nrf2/NF-kB regulation as a possible mechanism by which melatonin attenuates oxidative stress, and provide new insights for further studies of this indoleamine as a therapeutic co-adjuvant agent against T. cruzi infection.

Chagas disease, triggered by the flagellate protozoan Trypanosoma cruzi (T. cruzi) plays a potentially threat to historically non-endemic areas. Considerable evidence established that the immuno-endocrine balance could deeply influence the experimental T. cruzi progression inside the host's body. A high-resolution multiple reaction monitoring approach (MRMHR) was used to study the influence of melatonin on adrenal and plasma steroidal hormones profile of T. cruzi infected Wistar rats. Young (5 weeks) and middle-aged (18 months) male Wistar rats received melatonin (5 mg/Kg, orally) during the acute Chagas disease. Corticosterone, 11-dehydrocorticosterone (11-DHC), cortisol, cortisone, aldosterone, progesterone and melatonin concentration were evaluated. Interleukin-1 alpha and β (IL-1α and β), IL-6 and transforming growth factor beta (TGF-β) were also analyzed. Our results revealed an increased production of corticosterone, cortisone, cortisol and aldosterone in middle-aged control animals, thus confirming the aging effects on the steroidal hormone profile. Serum melatonin levels were reduced with age and predominantly higher in young and middle-aged infected rats. Melatonin treatment reduced the corticosterone, 11-DHC, cortisol, cortisone, aldosterone and progesterone in response to T. cruzi infection. Decreased IL-1 α and β concentrations were also found in melatonin treated middle-aged infected animals. Melatonin treated middle-aged control rats displayed reduced concentrations of TGF-β. Melatonin levels were significantly higher in all middle-aged rats treated animals. Reduced percentages of early and late thymocyte apoptosis was found for young and middle-aged melatonin supplemented rats. Finally, our results show a link between the therapeutic and biological effects of melatonin controlling steroidal hormones pathways as well as inflammatory mediators.

Chagas disease or American trypanosomiasis is caused by the protozoan Trypanosoma cruzi and is endemic of the Americas. The control of the disease is restricted to toxic and potentially teratogenic drugs, which limit the use during pregnancy. The use of food supplementation offers a safe and low-cost form to alleviate Chagas disease symptoms, mostly in areas with alimentary risk. For example, zinc demonstrates positive effects in immune response, including in Chagas disease during pregnancy. This study describes the innate response in pregnant rats chronically infected with T. cruzi and supplemented with zinc. Pregnant female Wistar rats, infected with T. cruzi, were treated with 20 mg/kg/day zinc sulfate and euthanized on the 18th day. Samples (plasma, splenocytes, and peritoneal exudate) were collected and several immune parameters (nitric oxide, RT1B, CD80/CD86, MCP-1, CD11b/c, NK/NKT, IL-2, IL-10, INF-cc, and apoptosis) evaluated. Under Zinc supplementation and/or T. cruzi infection, the gestation developed normally. Several innate immune parameters such as RT1B, CD80/CD86, MCP-1 expressing lymphocytes, IL-2, and IL-17 were positively altered, whereas nitric oxide, CD11b/c, NK/NKT, apoptosis, INF-γ, and corticosterone demonstrated a pro-pregnancy pattern. Our results indicated that zinc has diverse effects on immune response during pregnancy. An anti-T. cruzi immunity, as well as a pro-gestation response, were observed after zinc supplementation. The complete comprehension of zinc supplementation in pregnancy will base an adequate strategy to alleviate Chagas disease symptoms and propagation, especially for populations from endemic areas.

Although T. cruzi was identified as the cause of Chagas disease more than 100 years ago, satisfactory treatments still do not exist, especially for chronic disease. Here we review work suggesting that melatonin could have promise as a Chagas therapeutic. Melatonin has remarkably diverse actions. It is an immunomodulator, an anti-inflammatory, an antioxidant, a free radical scavenger, and has antiapoptotic and anti-aging effects. The elderly (aged 60 years or more) as a group are growing faster than any other age group. Here we discuss the major effects and the mechanisms of action of melatonin on aged T. cruzi-infected rats. Melatonin's protective effects may be consequences of its cooperative antioxidant and immunomodulatory actions. Melatonin modulates oxidative damage, inducing an antioxidant response and reversing age-related thymus regression. Its protective actions could be the result of its anti-apoptotic activity, and by its counteracting the excessive production of corticosterone. This review describes our work showing that host age plays an important and variable influence on the progression of systemic T. cruzi infection and supporting the hypothesis that melatonin should be considered as a powerful therapeutic compound with multiple activities that can improve host homeostasis during experimental T. cruzi infection.

Diseases associated with thyroid hypofunction have been the subject of studies in infectious models, since several authors have demonstrated a pivotal role of iodinated hormones (thyroxine and triiodothyronine) in the modulation of immune effector responses. Using a model of hypothyroidism induced by anti-thyroid drug, we investigated the influence of hypothyroidism in the course of acute Trypanosoma cruzi infection. For this, male Hannover Wistar rats were challenged with methimazole for 21 days (0.02% in drinking water), and water for control counterparts. After confirmation of the hypothyroidism, rats were intraperitoneally challenged with 1x10(5) blood trypomastigotes of the Y strain of T. cruzi. Our findings suggest that hypothyroidism impairs animal weight gain, but does not affect the health of essential organs. Interestingly, infected hypothyroid animals had a significant increase in thymic cell death, with consequent drop in lymphocyte frequency in whole blood (evaluated on the 11th day of infection). Analyzing the percentage of immune cells in the spleen, we found a strong influence of hypothyroidism as a negative regulator of B cells, and antigenic ability of macrophages (RT1b expression) in the course of the experimental chagasic infection. Enhanced serum IL-17A concentration was induced by T. cruzi infection, but hypothyroidism impaired the production of this mediator as seen in infected hypothyroid animals. Taken together, our work suggests for the first time that hypothyroidism may adversely interfere with the modulation of effective immunity in the early phase of Chagas' disease.

Trypanosoma cruzi is the causative agent of Chagas disease, which is endemic to subtropical and tropical Americas. The disease treatment remains partially ineffective, involving therapies directed to the parasite as well as palliative strategies for the clinical manifestations. Therefore, novel candidates for disease control are necessary. Additionally, strategies based on parasite inhibition via specific targets and application of compounds which improve the immune response against the disease is welcomed. Ghrelin is a peptide hormone pointed as a substance with important cardioprotective, vasodilatory, anti-apoptotic, anti-oxidative and immune modulatory functions. The aims of this study were to evaluate the immunomodulatory effects of ghrelin in male Wistar rats infected with the Y strain of T. cruzi. In order to delineate an immune response against T. cruzi mediated by ghrelin, we evaluated the following parameters: quantification of blood and cardiac parasites; analysis of cell markers (CD3+, CD8+, NK, NKT, CD45RA+, macrophage and RT1B+); nitric oxide (NO) production; lymphoproliferation assays; splenocyte apoptosis; and INF-γ, IL-12 and IL-6 quantification in sera. The animals infected with T. cruzi and supplemented with ghrelin demonstrated an upregulated pattern in macrophage and NO production, whereas an anti-inflammatory response was observed in T cells and cytokines. The low response against T. cruzi mediated by T cells probably contributed to a higher colonization of the cardiac tissue, when compared to infected groups. On the other side, the peptide decreased the inflammatory infiltration in cardiac tissue infected with T. cruzi. Ghrelin demonstrated a dual function in animals infected with T. cruzi. Further studies, especially related to the decrease of cardiac tissue inflammation, are needed in order to determine the advantages of ghrelin supplementation in Chagas disease, mostly for populations from endemic areas.

Prolactin (PRL) is a pleiotropic polypeptide hormone produced by the anterior pituitary gland and negatively controlled by dopamine. Some researchers have associated the immune regulatory functions of PRL with some infectious diseases like Toxoplasma gondii and T. cruzi. This work aimed to analyze the possible immuno-modulatory effects of this hormone through the subcutaneous administration of PRL during the experimental Chagas disease. On the 14th day post-infection (dpi), PRL triggered increased percentages of NK cells in treated infected animals as compared to the infected and untreated ones. For early and late apoptosis, our results showed that in chronically infected groups, PRL counteracted splenocyte apoptosis as revealed by the reduced percentages of both, early and late apoptosis. Reduced percentages of spleen CD4+ and CD8+ T cells were detected in infected PRL treated rats (60 days post-infection). Concerning to B cells, a significant increased percentage of these cells was found for all PRL treated infected animals (14th dpi), but no statistically significant alteration was observed on the 60th days post-infection. Furthermore, PRL treatment triggered a significant increase in the percentage of CD4+ T lymphocytes IFN-γ producers, while on the 60th dpi, a reduced percentage of IFN-γ in these cells was observed in prolactin-treated rats compared to infected and untreated ones. Enhanced serum IL-12 levels were detected in infected and PRL treated subjects (60th dpi). Only on 7th day post-infection, the flow cytometric analysis of CFSE-stained CD3+ T cells showed an enhanced proliferation of polyclonal stimulated T cells in PRL-treated and infected animals. In this study, we demonstrated that PRL can influence many aspects of the immune response during the experimental Chagas' disease, and this substance could be used as a supporting trial along with the conventional drug treatment.

Chagas disease is a tropical disease, endemic of the Americas and caused by the protozoan Trypanosoma cruzi. The classic transmission route of T. cruzi is based on the contact with feces from Triatominae insects containing trypomastigotes forms of the parasite. T. cruzi is also spread by oral and congenital forms, besides blood donation and organ transplant transmission. The parasite has a tropism to several organs and tissues, including heart, brain, digestive tract, muscles, placenta, and fetuses. The determination of parasite burden in organs is an important parameter for scientific assays related to parasite control and epidemiology. Among the procedures to detect and quantify T. cruzi, PCR demonstrates high sensitivity and specificity. In this study, we developed a simple and fast method to detect T. cruzi from fixed placentas and fetuses of Wistar rats. T. cruzi was detected only in tissues from infected animals, with different parasite burdens. Once the histology usually demonstrates some limitations such as low sensitivity and specificity to detect T. cruzi in fetuses, our methodology will be useful for fixed fetal tissues from organ banks. The detection of T. cruzi from gestational tissues will contribute to the elucidation of mechanisms related to congenital Chagas disease.

Although the exact etiology of Chagas disease is not completely elucidated, thymic atrophy and oxidative stress are believed to be important contributors to the pathogenesis during acute Trypanosoma cruzi (T. cruzi) infection. We hypothesized that exogenous melatonin, administered by gavage (5 mg/kg, p.o., gavage) to young (5 weeks old) and middle‐aged (18 months old) male Wistar rats, would modulate thymic oxidative damage and reverse the age‐related thymus regression during T. cruzi acute infection. Increased levels of superoxide anion (O2−) were detected in the thymus of infected animals, and treatment with melatonin reverted this response. We found reduced TBARS levels as well as a significant increase in superoxide dismutase (SOD) activity in the thymus of all middle‐aged melatonin‐treated animals, infected or not with T. cruzi. Furthermore, melatonin increased the thymic expression of SOD1 and SOD2 in middle‐aged control animals. Nox2 expression was not affected by melatonin treatment in young or middle‐aged animals. Melatonin reverted the age‐related thymic regression as revealed by the increase in thymus weight, total number of thymocytes, and reduction in age‐related accumulation of double‐negative thymocytes. This is the first report to directly examine the effects of melatonin treatment on the thymic antioxidant/oxidant status and thymic changes during T. cruzi infection. Our results revealed new antioxidant features that turn melatonin a potentially useful compound for the treatment of Chagas disease, a condition in which an excessive oxidative damage occurs.

Selenium (Se) is an essential micronutrient in the diet of mammals and has an important role in the immune function. Selenium is a key element in selenoproteins involved in the in the maintenance of the antioxidant defense. Diet with selenium is beneficial for the treatment of diseases correlated with high levels of oxidative stress, also observed in the Chagas disease. Chagas disease is a neglected disease caused by the protozoan Trypanosoma cruzi and several research groups are focused on the illness treatment. Immunomodulation of the infection using microelements is an important tool to avoid deleterious effects of the Chagas disease. Therefore, our objective was to evaluate the effects of selenium supplementation on pregnant Wistar rats infected with T. cruzi. Selenium treatment stimulated the weight and length of fetuses and placentas allied to the decrease of blood parasitemia. However, selenium demonstrated a low influence on T cells, diminishing the B cell population (CD45RA+). Moreover, the production of pro-inflammatory cytokines was downregulated under selenium administration. Low pro-inflammatory cytokines levels probably are related to the increase in the number of amastigote nests in infected and treated animals. Thus, selenium supplementation during pregnancy could impair the local placental immune response. Further studies are necessary to assess the interaction between selenium and the acute Chagas' disease during pregnancy, which will base future supplementation strategies.

Chagas disease afflicts 7 to 8 million people worldwide and congenital Chagas' disease usually leads to changes in the maternal environment, culminating in fetal adaptations. Several articles have described the importance of micronutrients on pregnancy, which is sensitive to infections. In Trypanosoma cruzi endemic regions, the Chagas disease is aggravated by the lack of micronutrients in an average diet, to which pregnant women are more susceptible. The aim of this study was to evaluate distinct T cells phenotypes and intracellular cytokines by flow cytometry in pregnant Wistar rats under zinc therapy during experimental Chagas' disease. Twenty female Wistar rats were infected with 1×105 blood trypomastigotes (Y strain) and 30days after infection the animals were mated and grouped: pregnant infected (PI–n=5), pregnant infected/zinc supplied (PIZ–n=5), pregnant control (PC–n=5), control/zinc supplied (PCZ–n=5). Zinc supplementation: 20mg of zinc/Kg/day (gavage) for 18days followed by euthanasia. The immune parameters showed: decreased percentages of CD62LlowCD44high surface marker for infected and treated group (PIZ) when compared to PI (p<0.05). Concerning to T regulatory cells (Treg cells), a significantly lower percentage of splenic Treg cells was found in the infected and treated group (PIZ) as compared to the PI group (p<0.05). The expression of the co-stimulatory molecule CD28+ displayed a significant reduced percentage in TCD8+ for infected and zinc treated group (PIZ) as compared to (PI). The percentages of CD4+/CD11a+ T cells subsets were lower on PIZ as compared to PI. Concerning to CD45RA+ (B lymphocytes) analysis, infected pregnant and treated group (PIZ) showed a significant decrease in CD45RA percentage when compared to (PI) (p<0.05). The intracellular cytokine profiles for TCD4+ and TCD8+ producing IL-4 and IFN-γ revealed that zinc treated and untreated infected pregnant group (PI and PIZ) displayed increased cytokines concentrations as compared to zinc treated and untreated pregnant controls (PC and PCZ). Our data revealed the involvement of zinc as a signaling molecule in the modulation of the inflammatory process and immune response which occurs during pregnancy of T. cruzi infected rats. Zinc acted in a dual fashion, modulating the host's immune response in a way to protect the organism against the deleterious effects of the infection and an overwhelming pro-inflammatory response during pregnancy.

Aging is linked with a thymic oxidative damage and some infectious diseases such as Chagas' disease may aggravate this process. The aim of this study was to evaluate the production of distinct cytokines as well as the antioxidant/oxidant status of the thymus and thymocytes populations during Trypanosoma cruzi (T. cruzi) infection. Young (5 weeks old) and aged (18 weeks old) male Wistar rats were inoculated with blood trypomastigotes forms of the Y strain of T. cruzi. On the 16th day after T. cruzi infection, increased concentrations of transforming growth factor beta (TGF-beta), interleukin (IL)-12, IL-17 were detected in aged infected subjects as compared to young infected ones. Interestingly, a reduction in the production of tumor necrose factor (TNF)-alpha was observed in aged infected rats when compared to young infected subjects. Aged-infected rats presented increased O-2(-) levels, compared to young counterparts. Significant raise in the generation of O-2 in aged infected animals, as compared to uninfected counterparts was observed. Up-regulated expression of Nox2 in the thymus of young and aged infected animals was observed. An increased SOD2 expression was detected in the thymus of young animals infected with T. cruzi, when compared to uninfected young rats. Aged animals showed reduced thymus weight and the number of thymocytes. Decreased percentages of SPCD4(+) and SPCD8(+)T cells were detected in aged and control groups when compared to young counterparts. In summary, this is the first data to directly examine the influence of aging on age-related dysfunctions during the acute phase of experimental Chagas disease. Concerning to oxidative stress, it is clear from our analysis that aged infected rats suffer a more intense oxidative damage when compared to young and infected ones. Age and infection triggered a dynamic interplay of cytokines, oxidative stress and thymic dysfunctions which led to impaired response from aged and infected rats. Such findings may have significant functional relevance in therapeutic strategies in order to reestablish the thymic immunological function which occurs in aged and T. cruzi infected subjects.

The purpose of this study was to investigate the effects of melatonin on selected biomarkers of innate and humoral immune response as well as the antioxidant/oxidant status (superoxide dismutase-SOD and reduced glutathione levels (GSH) to understand whether age-related changes would influence the development of acute Trypanosoma cruzi (T. cruzi) infection. Young-(5 weeks) and middle-aged (18 months) Wistar rats were orally treated with melatonin (gavage) (05 mg/kg/day), 9 days after infection. A significant increase in both SOD activity and GSH levels was found in plasma from all middle-aged melatonin-treated animals. Melatonin triggered enhanced expression of major histocompatibility class II (MHC-II) antigens on antigen-presenting cell (APC) and peritoneal macrophages in all treated animals. High levels of CD4(+)CD28-negative T cells (*P<.05) were detected in middle-aged control animals. Melatonin induced a significant reduction (***P<.001) in CD28-negative in CD4(+) and CD8(+) T cells in middle-aged control animals. Contrarily, the same group displayed upregulated CD4(+)CD28(+)T and CD8(+)CD28(+)T cells. Melatonin also triggered an upregulation of CD80 and CD86 expression in all young-treated groups. Significant percentages of B and spleen dendritic cells in middle-aged infected and treated animals were observed. Our data reveal new features of melatonin action in inhibiting membrane lipid peroxidation, through the reduction in 8-isoprostane, upregulating the antioxidant defenses and triggering an effective balance in the antioxidant/oxidant status during acute infection. The ability of melatonin to counteract the immune alterations induced by aging added further support to its use as a potential therapeutic target not only for T. cruzi infection but also for other immunocompromised states.