Lymphocyte subpopulations and neutrophil function in chronic human Chagas' disease

Neutrophils from patients with the cardiac clinical form of Chagas disease release less NETs than neutrophils from healthy individuals

INTRODUCTION

Chagas disease (CD) is a global health concern with approximately 12 000 deaths per year worldwide. In the chronic phase, about 30% of patients develop the cardiac clinical form, which presents symptoms associated with the presence of inflammatory cells in the cardiac tissue. Neutrophils are inflammatory cells able to modulate the chronic immune response against pathogens. These cells are capable of interacting with Trypanosoma cruzi, the aetiological agent of CD, and perform several effector functions, such as NET release. However, few studies have been carried out to investigate the role of these cells in the disease.

AIMS

To investigate the release of NETs by neutrophils from CD patients by measuring the amount of DNA and elastase released.

METHODS AND RESULTS

Measurement of DNA release by neutrophils from chronic CD patients presenting the indeterminate (IND group; n = 18) and cardiac (CARD group; n = 15) clinical forms and nonchagasic subjects (n = 18) stimulated with soluble antigen of T. cruzi was quantified using the Quant-iT™ PicoGreen^® dsDNA assay kit. Patients from CARD group release less DNA (117.3 ± 21.85 ng/mL; *P = .0131) than neutrophils from control (177.7 ± 58.41 ng/mL). Elastase enzyme degranulation was measured using the substrate N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide (SAAVNA). Absorbance values of elastase degranulation activity showed that only cells from healthy individuals presented a high release profile of elastase. Also, we found a negative correlation between DNA released concentration and risk of death (r = -.6574; *P = .0173); the lower the neutrophil DNA release from chagasic patients with cardiac event, the higher the risk of death.

CONCLUSION

These preliminary data show that patients with the cardiac form of CD release less NETs than nonchagasic individuals, raising the possibility that lower release of NETs enhances risk of death in CD patients with cardiac events.

Involvement of neutrophils in Chagas disease pathology

Chagas disease (CD) is a public health problem in Latin America. The acute phase presents nonspecific symptoms and most patients recover from acute parasitemia and undergo a prolonged asymptomatic phase. Several years later, about 30% of infected individuals develop chronic cardiopathy with progressive cardiomegaly, arrhythmia, thromboembolic events and heart failure. These symptoms suggest a persistent association with the presence of inflammatory infiltrate and tissue, and cellular destruction in the heart muscle. Nevertheless, few research studies have attempted to understand the role of inflammatory cells, such as neutrophils, in establishing the pathology and progression of CD. Only recently have some studies been performed with this intention. Despite this effort, the role of neutrophils in CD is still considered controversial. This review discusses the morphological and functional characteristics of neutrophils that describes their participation in the establishment and progression of Trypanosoma cruzi infection, through the development of its effector functions, such as release of lithic components, production of oxidative agents and release of inflammatory mediators capable of modulating the host immune response.

Presence of antigen-experienced T cells with low grade of differentiation and proliferative potential in chronic Chagas disease myocarditis

BACKGROUND

The main consequence of chronic Trypanosoma cruzi infection is the development of myocarditis in approximately 20-30% of infected individuals but not until 10-20 years after the initial infection. We have previously shown that circulating interferon-γ-secreting T cells responsive to Trypanosoma cruzi antigens in chronic Chagas disease patients display a low grade of differentiation and the frequency of these T lymphocytes decreases along with the severity of heart disease. This study thought to explore the expression of inhibitory receptors, transcription factors of type 1 or regulatory T cells, and markers of T cell differentiation, immunosenescence or active cell cycle in cardiac explants from patients with advanced Chagas disease myocarditis.

METHODOLOGY/PRINCIPAL FINDINGS

The expression of different markers for T and B cells as well as for macrophages was evaluated by immunohistochemistry and immunofluorescence techniques in cardiac explants from patients with advanced chronic Chagas disease submitted to heart transplantation. Most infiltrating cells displayed markers of antigen-experienced T cells (CD3(+), CD4(+), CD8(+), CD45RO(+)) with a low grade of differentiation (CD27(+), CD57(-), CD45RA(-), PD(-)1(-)). A skewed T helper1/T cytotoxic 1 profile was supported by the expression of T-bet; whereas FOXP3(+) cells were scarce and located only in areas of severe myocarditis. In addition, a significant proliferative capacity of CD3(+) T cells, assessed by Ki67 staining, was found.

CONCLUSIONS/SIGNIFICANCE

The quality of T cell responses and immunoregulatory mechanisms might determine the pattern of the cellular response and the severity of disease in chronic Trypanosoma cruzi infection.

Impaired phagocytic capacity driven by downregulation of major phagocytosis-related cell surface molecules elicits an overall modulatory cytokine profile in neutrophils and monocytes from the indeterminate clinical form of Chagas disease

The distinct ability of phagocytes to present antigens, produce cytokines and provide co-stimulatory signals may contribute to the severity of the outcome of Chagas disease. In this paper, we evaluate the phenotypic features of phagocytes along with the cytokine signature of circulating T-cells from Chagas disease patients with indeterminate (IND) and cardiac (CARD) clinical forms of the disease. Our data demonstrated that neutrophils from IND patients displayed an impaired ability to produce cytokines. A lower Trypanosoma cruzi phagocytic index and higher nitric oxide levels were characteristics of monocytes from IND. The impaired phagocytic capacity did not reflect on the levels of anti-T. cruzi IgG, but was detectable in the downregulation of Fc-γR, TLR and CR1 molecules. The monocyte-derived cytokine signature demonstrated that a down-regulated synthesis of IL-12 and a modulatory state were evidenced by a positive correlation between IL-12 and IL-10 with a lower synthesis of TNF-α. The down-regulation of MHC-II and CD86 in monocytes supports the occurrence of particularities in the APC-activation-arm in IND, and may be involved in the T-cell pro-inflammatory pattern counterbalanced by a potent IL-10 response. Our findings support the hypothesis that differential phenotypic features of monocytes from IND may be committed to the induction of a distinct immune response related to low morbidity in chronic Chagas disease.

Differing phagocytic function of monocytes and neutrophils in Chagas' cardiopathy according to the presence or absence of congestive heart failure

We evaluated the in vitro phagocytic function and the production of microbicidal oxygen radicals by monocytes and neutrophils of 9 Chagas' heart disease subjects with heart failure and 9 without the syndrome in comparison with 11 healthy subjects, by assessing phagocytosis of Saccharomyces cerevisiae and NBT reduction by peripheral blood phagocytes. Phagocytic index of monocytes of chagasics without heart failure was significantly 6.7 and 10.6 times lower than those of controls and chagasics with the congestive syndrome, respectively, due to a lesser engagement in phagocytosis and to an inability of these cells to ingest particles. Neutrophils also show in chagasics without heart failure PI 11.2 and 19.8 times lower than that of controls and chagasics with heart failure, respectively. The percent of NBT reduction was normal and similar for the three groups. Balanced opposite effects of cardiovascular and immune disturbances may be acting in Chagas' disease subjects with heart failure paradoxically recovering the altered phagocytic function.

Seroprevalence of Helicobacter pylori infection in chronic chagasic patients, and in the rural and urban population from Uberlândia, Minas Gerais, Brazil

As patients with chronic Chagas disease exhibit morphological and functional changes of the stomach (hypomotility and hypochlorhydria), malnutrition, immunological deficiency and high prevalence of peptic disease associated to Helicobacter pylori infection, the purpose of this study was to evaluate if the prevalence of H. pylori infection in chronic chagasic is higher than in non-chagasic individuals in the urban and rural population from Uberlândia, MG, Brazil. Serological determination of IgG antibodies to H. pylori was performed using a second-generation ELISA. Thus, 598 people were evaluated: 128 chagasic (CG), 222 non-chagasic living in urban area (U-NCG) and 248 non-chagasic living in rural area (R-NCG). Regarding the age range from 21 to 50 years, the prevalence of H. pylori infection in the CG (85.1%) was significantly higher than in the U-NCG (56.3%, p < 0.01) and the R-NCG (67.4%, p < 0.05). In the patients over 50 years, the prevalence in the CG (86.4%) was similar to the U-NCG (78.8%) and R-NCG (86.1%). Similar results were also found between the U-NCG and R-NCG for all age ranges, with prevalence rates of 29.1% and 35.3% for the age range from 5 to 13 years, and 47.2% and 40% for that from 14 to 20 years, respectively. We conclude that chagasic patients showed a higher seroprevalence of H. pylori infection than non-chagasic individuals, in the age range from 21 to 50 years, and that the prevalence of this infection was similar in the studied urban and rural non-chagasic population.

Administration of interferon-g to pregnant rats reverses the depressed adjuvant-induced arthritis of their chronically Trypanosoma cruzi-infected offspring

We demonstrated that administration of interferon gamma (IFN-gamma) to the inbred "I" strain of pregnant rats conferred partial resistance on their offspring to challenge with Trypanosoma cruzi. We now examine if this intervention also modifies the reportedly immunodepressed cellular responses which occur during chronic infection. Offspring were born to mothers undergoing one of the following procedures during gestation: subcutaneous injections of recombinant rat IFN-gamma, 50,000 IU/rat, five times/week for 3 weeks, which was started on the day of mating (IFN-Mo); infection with 10(6) trypomastigotes of T. cruzi at 7, 14, and 21 days after mating plus IFN-gamma treatment as given to the former group (TcIFN-Mo); the same protocol except that physiological saline was injected instead of IFN-gamma (Te-Mo); injection of physiological saline only (control-Mo). All offspring groups (N = 8-10/group) were infected at weaning and were assessed 90 days later for their adjuvant-induced arthritic response or levels of major T cell subsets in spleen and lymph nodes. TcIFN-Mo and IFN-Mo offspring showed a reestablished arthritic response, which remained within the range seen in controls. Immunolabeling studies on parallel groups of 90-day-infected offspring showed that the inverse CD4/CD8 cell ratio that is usually seen in lymphoid organs from these chronically infected rats (median 0.61) appeared to have recovered in the TcIFN-Mo and IFN-Mo groups (median 1.66 and 1.78, respectively) and was not different from uninfected controls (1.96). These studies indicate that early stimulation with IFN-gamma is able to reverse the immunosuppressive state that is usually present during the chronic period of the experimental infection.

Chronic Trypanosoma cruzi infection in the rat: cyclophosphamide-induced recovery of adjuvant arthritis correlates with changes in the levels of lymph node T-lymphocytes and class II+ cells

We have previously reported that treatment with cyclophosphamide (Cy) reversed the partial resistance of chronically Trypanosoma cruzi-infected rats to adjuvant-induced arthritis (AA) and caused a slight enhancement of arthritis in controls, when given 48 h before induction. To ascertain whether this Cy effect could be associated with regional changes of immunocompetent cells, popliteal lymph nodes were studied for their T-cell subsets and cells carrying class II major histocompatibility (MHC) antigens (1-A and 1-E molecules). Analysis at the time of arthritis induction revealed that infected rats receiving Cy 48 h earlier appeared to have recovered from the inverse balance of major T-cell subsets and showed 1-E+ cells lowered to normal, whereas values from control rats remained unchanged by Cy treatment. Establishment of AA was associated with substantial changes in the phenotype of lymph node cells that drained the affected limb. Changes were equally recorded in control and infected arthritic rats, and consisted of a significant raise of CD4+ and I-A+ cells along with lowered numbers of CD8+ and I-E+ cells. Treatment with Cy lowered even further the levels of CD8+ cells, while causing no affectation in the number of CD4+ cells that remained increased as in the arthritic counterparts receiving no Cy. Comparative analysis of class II MHC+ cells in Cy-treated rats revealed an additional decrease of I-E+ cells in draining lymph nodes from infected and control rats, which coincided with a simultaneous increase in I-A+ cells in the uninfected group. It is suggested that a deletion of a regulatory T-cell subset as well as an improved presentation of arthritogenic peptides may at least underlie the Cy-induced enhancement of the arthritic response.

NK and LAK functions in human chronic Chagas disease

Natural killer (NK) and lymphokine activated killer (LAK) functions were measured in 40 patients with chronic Chagas disease divided into asymptomatic/indeterminate (18) and symptomatic forms (22) and in 24 healthy controls. A chromium release assay was used employing K562 or P815 cell lines as targets. There was no difference in either NK or LAK activity between the three groups. A small number of patients in each group showed results above or below the normal range for controls. However, there was no correlation between NK and LAK values in the same individual. In conclusion, NK immunosuppression associated with human chronic Chagas disease.