Anti-laminin and specific antibodies in acute Chagas disease

Heat-killed Trypanosoma cruzi induces acute cardiac damage and polyantigenic autoimmunity

Chagas heart disease, caused by the protozoan parasite Trypanosoma cruzi, is a potentially fatal cardiomyopathy often associated with cardiac autoimmunity. T. cruzi infection induces the development of autoimmunity to a number of antigens via molecular mimicry and other mechanisms, but the genesis and pathogenic potential of this autoimmune response has not been fully elucidated. To determine whether exposure to T. cruzi antigens alone in the absence of active infection is sufficient to induce autoimmunity, we immunized A/J mice with heat-killed T. cruzi (HKTC) emulsified in complete Freund's adjuvant, and compared the resulting immune response to that induced by infection with live T. cruzi. We found that HKTC immunization is capable of inducing acute cardiac damage, as evidenced by elevated serum cardiac troponin I, and that this damage is associated with the generation of polyantigenic humoral and cell-mediated autoimmunity with similar antigen specificity to that induced by infection with T. cruzi. However, while significant and preferential production of Th1 and Th17-associated cytokines, accompanied by myocarditis, develops in T. cruzi-infected mice, HKTC-immunized mice produce lower levels of these cytokines, do not develop Th1-skewed immunity, and lack tissue inflammation. These results demonstrate that exposure to parasite antigen alone is sufficient to induce autoimmunity and cardiac damage, yet additional immune factors, including a dominant Th1/Th17 immune response, are likely required to induce cardiac inflammation.

BAFF mediates splenic B cell response and antibody production in experimental Chagas disease

BACKGROUND

B cells and antibodies are involved not only in controlling the spread of blood circulating Trypanosoma cruzi, but also in the autoreactive manifestations observed in Chagas disease. Acute infection results in polyclonal B cell activation associated with hypergammaglobulinemia, delayed specific humoral immunity and high levels of non-parasite specific antibodies. Since TNF superfamily B lymphocyte Stimulator (BAFF) mediates polyclonal B cell response in vitro triggered by T. cruzi antigens, and BAFF-Tg mice show similar signs to T. cruzi infected mice, we hypothesized that BAFF can mediate polyclonal B cell response in experimental Chagas disease.

METHODOLOGY/PRINCIPAL FINDINGS

BAFF is produced early and persists throughout the infection. To analyze BAFF role in experimental Chagas disease, Balb/c infected mice were injected with BR3:Fc, a soluble receptor of BAFF, to block BAFF activity. By BAFF blockade we observed that this cytokine mediates the mature B cell response and the production of non-parasite specific IgM and IgG. BAFF also influences the development of antinuclear IgG and parasite-specific IgM response, not affecting T. cruzi-specific IgG and parasitemia. Interestingly, BAFF inhibition favors the parasitism in heart.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate, for the first time, an active role for BAFF in shaping the mature B cell repertoire in a parasite infection.

Autoantibodies in nonautoimmune individuals during infections

Infections can act as environmental triggers inducing or promoting autoimmune disease in genetically predisposed individuals. Identification of microbial peptides similar to self-tissues may by molecular mimicry, provide the inducing mechanism for an immune response. The aim of this study was to identify autoantibodies (autoAbs) in nonautoimmune individuals during acute bacterial, viral, or parasitic infections. Specific Abs or specific infections with an increased autoAb load may shed insight into the mechanisms of autoimmune disease. Sera from 88 patients with acute infections (41 bacterial, 23 viral, 17 parasitic, and 7 rickettsial) were tested by the ELISA method for antinuclear antibodies (ANA) 8 Pro, and Abs to thyroid peroxidase (TPO), thyroglobulin, phospholipids, annexin-V, laminin, anti-Saccharomyces cervisiae (ASCA), and prothrombin, along with 80 normal controls. Elevated titers of Abs to annexin-V and prothrombin were the most prevalent in viral, parasitic, and rickettsial infections and to laminin in viral and parasitic infections. Elevated titers of ASCA and ANA were found in viral and bacterial infections. Antiphospholipid Abs were found in parasitic and Q-fever infections. Thirty-four individuals harbored elevated titers of at least two Abs. An autoAb burden was detected in individuals with hepatitis A, hepatitis B, toxoplasma or Q-fever infections. In nonautoimmune individuals with various (bacterial, viral, parasitic, and rickettsial) infections, elevated titers of Abs to annexin-V, prothrombin, laminin, ASCA, ANA, and phospholipids were most frequently detected.

Changes in isotype composition and antigen recognition of anti-Trypanosoma cruzi antibodies from acute to chronic Chagas disease

This report describes differences in humoral immune response of acute and chronic phases of human Chagas disease. The reactivities of IgG, IgM, and IgA anti-Trypanosoma cruzi antibodies in serum samples from both groups of patients were compared by enzyme-linked immunosorbent assay (ELISA) employing either one of four antigenic fractions: mouse laminin (LAM), which reacts through Gal alpha 1-3Gal epitopes expressed on trypomastigote surface: whole intact trypomastigotes (TCT); trypomastigotes excreted/secreted antigens (TESA); and epimastigote alkaline extract (EAE). The selection of T. cruzi antigen preparations was based on their relative content of surface and internal antigens found in trypomastigote forms. The proportion of IgG reactive to carbohydrate epitopes was assessed through the decay of IgG reactivity from acute and chronic sera after m-periodate oxidation of solid-phase bound antigens. Trypomastigote and TESA antigens recognized by IgG from acute and chronic sera were also compared by immunoblotting. ELISA and immunoblotting data showed that: (1) the proportion of IgG directed to trypomastigote surface antigens was higher in acute than in chronic sera, whereas the opposite was found for internal antigens, (2) acute sera contained a higher percentage of IgG reactive to trypomastigote carbohydrate epitopes than chronic sera, and (3) anti-T. cruzi IgA was found exclusively in acute sera and led to 100% positivity when LAM, TCT, and TESA were employed as antigens. IgA ELISA with these antigens and IgG immunoblotting pattern with TESA could be useful as serological markers for the acute phase of human Chagas disease.

Distribution of alpha-galactosyl-containing epitopes on Trypanosoma cruzi trypomastigote and amastigote forms from infected Vero cells detected by Chagasic antibodies

Reactivity of different Trypanosoma cruzi developmental forms with purified Chagasic anti-alpha-galactosyl antibodies (anti-Gal) was studied using epimastigotes from axenic cultures, trypomastigotes and amastigotes from infected Vero cell cultures, and an immunogold labeling method as observed by electron microscopy. Epimastigotes were poorly labeled, whereas extracellular trypomastigotes and amastigotes bound heterogeneously to the antibody with many cells being intensely labeled at the cell surface, including the membrane lining the cell body, the flagellum and the flagellar pocket. Parasites with poor labeling at the cell surface generally had several gold particles within the cell, mostly in cytoplasmic vacuoles. The Golgi complex of trypomastigotes was strongly labeled. Intracellular parasites were labeled at the parasite cell surface or within vacuolar structures. The expression in T. cruzi-infected Vero cells of alpha-galactosyl antigenic structures acquired from the parasite was shown by moderate labeling with Chagasic anti-Gal of the membrane lining parasite-free outward cell projections. The reactivity with purified anti-Gal from healthy individuals at the same concentrations of Chagasic anti-Gal was poor, with gold particles appearing in the nucleus and cytoplasm but not at the cell surface. It paralleled the labeling with Bandeireae simplicifolia IB-4 lectin. The results provide a basis for autoimmune reactions involving anti-Gal from chronic Chagasic patients.

Lytic antibody titre as a means of assessing cure after treatment of Chagas disease: a 10 years follow-up study

A complement-mediated lysis test (CoML) using living trypomastigotes was compared with conventional serological methods and with haemoculture. Over a 10 years follow-up period evidence was obtained which supported the view that chagasic patients, treated with nitroheterocyclic drugs, in whom CoML had reverted to negative, might be considered cured despite conventional serology remaining positive.

Toxicity of sera from individuals with Chagas' disease to cultured rat embryos: role of antibodies to laminin

In previous studies antilaminin antibodies in the sera of immunized monkeys and rats were found to be toxic to cultured rat embryos. In order to extend these studies to humans, head-fold stage rat embryos were cultured for 48 hours on ten different serum samples from individuals with Chagas' disease. All embryos (n = 20) cultured on these sera were found to be abnormal. Using ELISA, Western immunoblot, and indirect immunofluorescence it could be shown that antibodies in these sera reacted with laminin. That these antilaminin antibodies were, at least in part, responsible for the toxicity was indicated 1) by reduced cultured embryo toxicity for six of seven serum samples after pre-absorption with purified laminin, 2) by demonstrating a relationship between the amount of affinity-purified antilaminin IgG added to control serum for culture and the severity of embryo abnormalities seen at the end of culture, and 3) by the sera's failing to react with other basement membrane proteins, including type IV collagen, fibronectin, osteonectin, and heparan sulfate proteoglycan.

Direct lysis of Trypanosoma cruzi: a novel effector mechanism of protection mediated by human anti-gal antibodies

Anti-gal antibodies directed against a carbohydrate epitope present in mouse laminin (galactosyl alpha 1-3 galactose) and detected in high levels in sera from patients in the acute phase of Chagas disease are responsible for the direct lysis (DL) of Trypanosoma cruzi blood forms independent of either the classic or alternative complement pathways. Furthermore, the lectins Euonymus europaeus (EE) specific for the carbohydrates gal alpha 1-3 gal present a similar lytic activity against T. cruzi at the same concentrations of purified anti-gal antibodies. The DL activity was tested with several other lectins but Concanavalin A (Con A) specific for alpha-D-mannose and alpha-D-glucose was the only one also presenting lytic activity. The lectins and anti-gal antibodies lytic activity can be inhibited by specific carbohydrates suggesting that this phenomenon is related to the capability of these lectins or anti-gal antibodies to bind to a crucial surface component of T. cruzi. Moreover, the infectivity of T. cruzi blood forms to mice was clearly inactivated by incubation with acute chagasic sera (ACS) but not by ACS absorbed by immunoaffinity chromatography with mouse laminin, a strong evidence that high levels of anti-gal antibodies participate in the decline of the parasitaemia from the acute to the chronic phase in Chagas disease.

Distribution of carbohydrates recognized by the lectins Euonymus europaeus and concanavalin A in monoxenic and heteroxenic trypanosomatids

We observed a wide distribution of the carbohydrate epitopes galactosyl alpha(1-3)galactose (gal alpha1-3 gal), alpha-glucoside and alpha-mannoside in mono- and heteroxenic trypanosomatids by using fluorescein-labelled lectins of Euonymus europaeus (EE) and Concanavalin A (Con A) as well as sera from acute chagasic patients who have very high levels of anti-gal alpha(1-3)gal antibodies. The direct fluorescence test for gal alpha1-3 gal with EE was positive at minimum concentrations of 6 micrograms/ml for heteroxenic trypanosomatids and 0.7 micrograms/ml for monoxenic ones and for the plant parasite, Phytomonas. On the other hand, heteroxenic trypanosomatids that infect vertebrates bound ten-fold more Con A than monoxenic flagellates and Phytomonas. These data were confirmed in ELISA and Western Blot assays carried out with peroxidase-labelled EE and Con A. Euonymus europaeus recognized several glycoproteins in all trypanosomatids that we tested. Con A, however, recognized a glycoprotein cluster in heteroxenic protozoa, which ranging from 60-120 kDa, seemed to lack monoxenic parasites and Phytomonas. These findings suggest that alpha-D-mannose and alpha-D-glucose might play an important role in the interaction between trypanosomatids and vertebrate hosts.