Complement component C1q enhances invasion of human mononuclear phagocytes and fibroblasts by Trypanosoma cruzi trypomastigotes.

Internalization and infectivity of Trypanosoma cruzi trypomastigotes by macrophages is enhanced by prior treatment of parasites with normal human serum. Heating serum or removing C1q from serum abrogates the enhancement, but augmentation of attachment and infectivity is restored by addition of purified C1q to either serum source. Although both noninfective epimastigotes (Epi) and vertebrate-stage tissue culture trypomastigotes (TCT) bind C1q in saturable fashion at 4 degrees C, internalization by monocytes and macrophages of TCT but not Epi-bearing C1q is enhanced in comparison to untreated parasites. Adherence of human monocytes and macrophages to surfaces coated with C1q also induces a marked enhancement of the internalization of native TCT. C1q enhances attachment of both Epi and TCT to human foreskin fibroblasts, but only when C1q is on the parasite and not when the fibroblasts are plated on C1q-coated surfaces. Only TCT coated with C1q show enhanced invasion into fibroblasts. Although trypomastigotes produce an inhibitor of the complement cascade which limits C3 deposition during incubation in normal human serum, C1q binds to the parasite and enhances entry of trypomastigotes into target cells.

Peripheral nervous system damage in experimental chronic Chagas' disease.

Electromyographic and histopathologic studies were performed in Rockland mice chronically infected with CA-I Trypanosoma cruzi strain. At 4 months post-infection the emg failed to show spontaneous activity, but a diminished interference pattern was detected in half of the infected group, while mean motor unit potential amplitude and duration were increased, compared with controls. An active denervation was observed at 6 months which persisted up to 9 months, when motor unit potential showed a significantly lower mean activity and duration. At 12 months most of the infected mice developed a reduced interference pattern, polyphasic motor unit potential increase with higher duration and amplitude than controls. Histopathologic studies showed myositis with perivascular involvement as well as intramuscular neuritis, especially at 4 and 12 months. Atrophic and hypertrophic fibers were seen. Few amastigote nests were detected. Inflammatory neuropathy with the demyelinated fibers and scanty axonal degeneration were the most common features in all infected mice. Mild myelinated fiber loss was only evident after 12 months. Endoneural parasites were seen only in the perineural macrophagic cells. These findings suggest that the neurogenic mechanism involved in the pathogenesis of muscle damage in this experimental model of chronic Chagas' disease consistently has been overlooked. The features registered here suggest that T. cruzi-infected mice developed a bimodal muscle denervation with an early acute period at any time before month 4, followed by reinnervation with a subsequent new acute denervation period by month 6, followed in turn by a slow later reinnervation.

The neuromuscular pathology of experimental Chagas' disease.

In this work, we describe skeletal muscle, neuromuscular junction, nerve and spinal cord lesions in the mouse model system of Chagas' disease. Myositis was a common finding and Trypanosoma cruzi amastigote nests were frequently found in the muscle fibers. Angular atrophy, targetoid fibers, groups of atrophic fibers, fibrosis, myofiber necrosis and phagocytosis of cellular debris were also observed. The neuromuscular junction studies showed degeneration of intramuscular nerve fibers, swelling and distortion of nerve endings and multiple ramifications on the same muscle fiber. Collateral, terminal and ultraterminal axonal sprouts were also present. Inflammatory neuropathy was seen in all of the infected mice. Demyelination, axonal degeneration, remyelination and axonal regeneration were observed in the transverse sections. There was an average reduction of 29% in the total number of myelin fibers. The teasing of single myelin fibers showed segmental and paranodal demyelination and remyelination more frequently than axonal degeneration and regeneration. The lumbar spinal cords presented inflammatory cell infiltration associated with tissue destruction. Amastigote nests were found in 3 out of the 8 infected mice studied. There was a mean loss of 21% of the large cytoneurons of the anterior horn of the lumbar spinal cord.

Histopathology of the heart conducting system in experimental Chagas disease in mice.

Although mice infected with Trypanosoma cruzi develop a wide variety of electrocardiographic (ECG) alterations, the typical isolated right bundle branch block or its association with the left anterior hemiblock patterns are not found in this model. This has been explained as related to topographic differences in the anatomy of the murine conducting system. However, there is no conclusive evidence that the murine conducting system differs from the human system. In this study, the anatomy of the murine conducting system is described, as well as its involvement in the chronic stages of experimental infection. 24 three-month-old C3H mice were infected with 50 bloodstream forms of T. cruzi, Tulahuén strain. Animals were killed after 3, 8 and 12 months. Whole frontal sections of the heart, including the conducting system, were serially studied. The sinoatrial node was located in the right atrial appendage, or in the junction between the superior vena cava and the right atrium, or "riding" on the interatrial septum. The atrioventricular (A-V) node and the His bundle showed a similar anatomic course to that in man. Therefore, there was no important anatomical difference that might have explained the lack of the ECG patterns observed in human chagasic myocardiopathy. The inflammatory involvement and the lesions of the conducting system were diverse and rarely severe. No significant difference was observed in animals killed at different times. The lesions in the working myocardium were similar to those observed in humans (chronic inflammatory infiltrates). Nevertheless, the topography of lesions was different: there was a selective involvement in the neighbourhood of the A-V groove.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation by Percoll gradient centrifugation and radiolabeling of bloodstream forms of Trypanosoma cruzi.

A method to isolate T. cruzi bloodstream forms was designed taking advantage of Percoll self-generated gradients and isopycnic centrifugation, resulting in a good resolution between parasites and host cells. Purified parasites incorporated 3H-uridine giving values of 23% precipitable by TCA. Viability of the parasites was totally preserved as evidenced by the "in vivo" infectivity assays.

[Trypanosoma cruzi: induction of changes in the peripheral nervous system in different strains of mice]. / Trypanosoma cruzi: inducción de alteraciones del sistema nervioso periférico en diferentes cepas de ratones.

This study has been designed to find an easy method to evaluate the motor unit alterations induced during experimental T. cruzi infections. Different mouse strains infected with three strains of T. cruzi were used to perform conventional needle electromyography, in one of the lower limb hamstring muscles; amplitude, duration and number of phases of single motor unit potentials were measured. The following parasite strain to mouse strain relationship was investigated, in mice inoculated intraperitoneally with bloodstream forms of T. cruzi: Tulahuen and C3H/HeN, C57Bl, Balb/c, Swiss; CA-I and C3H/HeN, Rockland, NIH; RA and C3H/HeN, Rockland. T. cruzi-induced denervating alterations were found in both C3H/HeN and C57Bl mice infected with the Tulahuen strain, as well as in C3H/HeN mice inoculated with the CA-I strain. Moreover, CA-I trypomastigotes could produce primary muscle changes in C3H/HeN and NIH mice. The technique employed in this investigation proved to be an easy and adequate way to detect changes within the motor unit during T. cruzi infection in mice.

Lytic rabbit IgG for tissue culture trypomastigotes of Trypanosoma cruzi alters the extent and form of complement deposition.

Infective and vertebrate stages of Trypanosoma cruzi are resistant to lysis by the alternative pathway of complement. To further elucidate the mechanism of complement evasion and to study how some immune sera render the infective stage sensitive to lysis, we compared the interaction of complement components C3 and C9 with the surface of complement susceptible, vector stage epimastigotes and vertebrate stage trypomastigotes of T. cruzi. Our studies showed that, upon incubation in human serum, complement resistant tissue culture trypomastigotes (TCT) bound five- to eightfold less C3 or C9 than complement sensitive epimastigotes (Epi). C3 bound to Epi is mainly in the hemolytically active C3b form, while TCT bear predominantly the hemolytically inactive iC3b fragment, which cannot participate in C5 convertase formation or lead to deposition of the lytic C5b-9 complex. Three- to sixfold more C3 and two- to threefold more C9 were deposited on TCT when lytic rabbit immune IgG with broad specificity was used to sensitize the parasites, and nearly one-half of bound C3 was present as C3b. In contrast, a comparison of three different sources of IgG from immune human serum showed a less clear correlation between the titer or specificity of anti-T. cruzi antibody, enhancement of C3 or C9 deposition, change in the form of bound C3, or killing. These results show that lytic rabbit IgG for T. cruzi changes the form and amount of bound complement components in anticipated fashion, but that human immune IgG does not give predictable changes in the extent or form of C3 or C9 deposition.

In vitro inactivation of complement by a serum factor present in Junin-virus infected guinea-pigs.

A serum factor(s) of guinea-pigs infected with Junin virus, the etiological agent of Argentine haemorrhagic fever, is endowed with a potent anticomplementary activity. It is resistant to heat (56 degrees, 30 min) and elutes from a Sephadex G-200 column between albumin and haemoglobin. It is ineffective in the presence of EDTA or EGTA and does not sediment at 82,000 g. It has no direct effect on C4 unless functional Cl is present. However, it induces Cl activation that consumes C4 haemolytic activity in normal human and guinea-pig sera. The evidence presented in this report demonstrates that the complement activation observed in experimental Argentine haemorrhagic fever is at least in part due to a direct effect of this serum factor on the classical complement pathway.

Antibody-dependent cytotoxicity of human and mouse mononuclear cells against Trypanosoma cruzi epimastigotes.

Human peripheral mononuclear cells were cytotoxic to antibody-sensitized Trypanosoma cruzi epimastigotes. The cytotoxic effect depended on the concentration of effector cells and antiserum, and was progressive until 17 hr of incubation at 28 degrees C. After 3 hr of incubation the highest specific activity was achieved at a 50:1 effector to target cell ratio. A nonspecific cytotoxic effect in the absence of antiserum was observed at a 100:1 parasite to cell ratio or after 17 hr of incubation. When the human mononuclear cell population was depleted of adherent cells by Sephadex G-10 filtration or adsorption to glass, the cytotoxic effect was greatly reduced. Similar results were obtained using mouse spleen cells, indicating that only the adherent cells were cytotoxic to sensitized T. cruzi in both systems. When human mononuclear cells were incubated with amobarbital, cyanide, azide, or aminotriazole, an inhibition of cytotoxicity against sensitized T. cruzi was observed, suggesting that oxygen reduction products and myeloperoxidase were involved in the destruction of sensitized T. cruzi epimastigotes by normal human mononuclear cells.

Developmentally regulated expression by Trypanosoma cruzi of molecules that accelerate the decay of complement C3 convertases.

We recently showed that culture-derived metacyclic trypomastigotes (CMT), but not epimastigotes (Epi), of the Miranda 88 strain of Trypanosoma cruzi evade lysis by the human alternative complement pathway because of inefficient binding of factor B to complement component C3b on the parasite surface. These results suggested that CMT and tissue-culture-derived trypomastigotes (TCT), which also activate the alternative pathway poorly, might produce a molecule capable of interfering with factor B binding to C3b. We now demonstrate that CMT and TCT lysates, as well as molecules spontaneously shed from CMT and TCT but not Epi, accelerate decay of 125I-labeled factor Bb from the alternative-pathway C3 convertase (C3bBb) assembled on zymosan or Epi and also accelerate decay of the classical-pathway C3 convertase (C4b2a) on sheep erythrocytes. Parasites metabolically labeled with [35S]methionine spontaneously shed a limited number of radioactive components ranging in molecular mass from 86 to 155 kDa for trypomastigotes and 25 to 80 kDa for Epi. Decay-accelerating activity within supernatants is inactivated by papain and is coeluted with 35S-containing polypeptides on FPLC anion-exchange chromatography, suggesting that the active constituents are protein molecules. Molecules with decay-accelerating activity may explain the developmentally regulated resistance to complement-mediated lysis in infective and vertebrate stages of the T. cruzi life cycle.

Phagocytosis of Trypanosoma cruzi by human polymorphonuclear leukocytes.

Phagocytosis of culture forms of Trypanosoma cruzi was assayed by a radioisotopic method. Purified polymorphonuclear leukocytes (PMN) were mixed with 3H-uridine-labeled T. cruzi epimastigotes in the presence or absence of anti-T. cruzi antibodies. The reaction was stopped by adding N-ethyl-maleimide, and noningested parasites were lysed by complement. The percentage of radioactivity incorporated into the PMN pellet was recorded. The phagocytosis reaction was rapid, yielding maximum incorporation at 30 min at which point the radioactivity associated with the PMN cells decreased through release of the isotope to the supernatant. The degree of incorporation of radio-labeled parasites was a function of the effector/target cell ratio and the antibody concentration. The method is suitable for the quantitative determination of phagocytosis of T. cruzi by normal PMN.

Trypanosoma cruzi: sequence of phagocytosis and cytotoxicity by human polymorphonuclear leucocytes.

We have studied the relationship between phagocytosis and cytotoxicity of human polymorphonuclear leucocytes (PMN) to sensitized Trypanosoma cruzi. Assays were done simultaneously using [3H]-uridine labelled epimastigotes as target cells. Phagocytosis was evaluated by the uptake and cytotoxicity by the release of parasite associated [3H]-uridine. Both reactions reached maximum levels at the same effector- to target-cell ratio and antibody concentration. Uptake of epimastigotes by PMN was highest at 30 min and intracellular disruption and release of parasite debris took place later. In conditions that precluded repeated uptake of sensitized radiolabelled T. cruzi, the release profile of [3H]-uridine from PMN that contained intracellular parasites was similar to that of the standard cytotoxic assay. However, as the ingestion phase was separated from the release step, no lag in the onset of the reaction was observed. Although we cannot rule out extracellular killing, the results of this study demonstrate that the bulk of damaged T. cruzi epimastigotes had been previously internalized by the PMN.

Peripheral blood leukocytes of patients with Argentine hemorrhagic fever as effectors of antibody-dependent cell-cytotoxicity.

Peripheral blood mononuclear cells (PBMC) and polymorphonuclear leukocytes (PMNL) of patients with Argentine hemorrhagic fever (AHF) were tested as effectors (E) of antibody-dependent cell cytotoxicity (ADCC). 51Cr labeled chicken red blood cells (CRBC) coated with anti-CRBC or normal rabbit serum were used as targets (T). Three ADCC assays were performed with both effectors from patients: on admission (I), 4 days after the transfusion of immune plasma (II), and 30 days after the clinical onset (III). The ADCC values obtained displayed high variation between individuals. From the linear portions in the curves representing specific 51Cr release vs. E:T ratio plots, extrapolations were made to determine lytic units (LU), defined here as effector concentrations required to lyse 50% of the targets. The results were expressed as LU in 10(6) effector cells. The killing activity ranges of patients' PMNL (I = 1.04 +/- 0.34; II = 2.22 +/- 0.66; and III = 2.08 +/- 1.18) were not significantly different from that of 21 normal controls (1.19 +/- 0.36), except for range II (P less than 0.01). ADCC activity ranges of patients' PBMC (I = 3.40 +/- 1.06; II = 3.16 +/- 1.60; and III = 1.93 +/- 0.42) were not significantly different from that determined in 12 healthy subjects (1.86 +/- 0.40). These results demonstrate that patients' PBMC and PMNL can perform ADCC with efficiency comparable to normal effector cells, during the acute period of AHF, and in early convalescence. Consequently, ADCC can be a relevant mechanism in the clearance of Junin virus-infected cells.

Biochemical characterization of a factor produced by trypomastigotes of Trypanosoma cruzi that accelerates the decay of complement C3 convertases.

Infective- and vertebrate-stage trypomastigotes of Trypanosoma cruzi resist serum killing by the alternative complement pathway, whereas noninfective vector-stage epimastigotes, from which trypomastigotes derive, are serum-sensitive. This form of developmental preadaption is commonly observed in protozoan parasites, but its mechanisms are poorly understood. We have demonstrated previously that trypomastigotes spontaneously shed molecules which interfere with formation and accelerate the intrinsic decay of complement C3 convertases, a finding which may explain the evasion of complement lysis by trypomastigotes. We now describe the partial purification and characterization of the T. cruzi C3 convertase inhibitor from the supernatant of culture metacyclic and tissue culture trypomastigotes. Decay-accelerating activity for both classical and alternative pathway C3 convertases copurifies on anion-exchange fast protein liquid chromatography and chromatofocusing with 35S-labeled molecules of 87-93 kDa, pI 5.6-5.8. The labeled components are destroyed by papain and retained on concanavalin A-Sepharose, procedures which remove functional decay-accelerating activity from the supernatant. The 87-93-kDa components are immunoprecipitated by sera from patients chronically infected with T. cruzi, but not by antisera to any known regulatory proteins of the human complement cascade. Lytic activity for tissue culture trypomastigotes in chagasic sera is associated with antibody reactivity against the 87-93-kDa 35S-labeled components and with inhibition of decay-accelerating activity. The T. cruzi factor is the first developmentally regulated microbial complement inhibitor to be biochemically characterized.

Argentine hemorrhagic fever. Alterations of the complement system and anti-Junin-virus humoral response.

We investigated immunologic mechanisms and the role of complement in the pathogenesis of Argentine hemorrhagic fever, a disease caused by the Junin virus, a member of the arenavirus group. Total serum complement activity was reduced to 68 per cent of control values in patients with severe or moderate disease (P less than 0.001). C2, C3 and C5 values were also low (12 to 60 per cent) during the early acute period of the disease. However, serum C4 content was increased to 160 per cent of the control values in the same patients. Total complement activity returned to normal with clinical and laboratory recovery, at the time of detection of antibodies against Junin virus. C1q reactive material was found in four of 19 cases and no relation to the evolution of the disease could be established. These results suggest that immune complexes are not important in the pathogenesis of Argentine hemorrhagic fever, but that activation of the complement system has a role.