Publisher Summary Among the protozoa of the Trypanosomatidae family, a large number of species represent agents of diseases, such as Chagas' disease. This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa. Protozoa of the Trypanosomatidae family show, during their, life cycle, several forms which can be easily identified by light microscopy in Giemsa-stained preparations. The chapter also explains the life cycle of T. cruzi. In the life cycle of T. cruzi, there are forms which are able to divide. There is one form, considered to be highly differentiated and responsible for the infectivity of these protozoa, which does not divide. It is highlighted that the trypomastigote form can transform into a rounded form which possesses a free flagellum. This form, which appears in the stomach, is able to transform into either short epimastigotes that start a process of multiplication in the intestinum or into long epimastigotes which move to the more posterior region of the digestive tract of the bug. Cell surface is also emphasized in the chapter.

Cell Biology of Trypanosoma cruzi

Publisher Summary Trypanosoma cruzi (T. cruzi), the causative agent of Chagas disease, is a digenetic trypanosomatid, which circulates in the bloodstream of the vertebrate host as trypomastigotes and has an obligatory intracellular phase in which the parasite multiplies as amastigotes, which differentiate into trypomastigotes. From an immunological point of view, therefore, the parasite presents stages that are directly exposed to the effector elements of the immune response, such as antibodies and macrophages, as well as stages that are sequestrated within host cells. T. cruzi infection is characterized by an acute phase with large numbers of parasites and by a sub-patent chronic phase in which circulating and tissue stages are difficult to detect. The mechanisms involved in the resistance to the parasite and in the control of parasitism during the chronic phase are not known. Chagas disease is life-long and spontaneous cures do not occur. There is increasing evidence that auto-immune processes participate in the pathogenesis of the cardiac and digestive forms of the disease. These many obscure aspects and challenging problems explain the increasing use of T. cruzi as a model for the study of humoral and cellular immunity in both basic and applied immunology.

Immunity to Trypanosoma cruzi.

In a prospective study, serum and plasma samples from 17 patients with kala-azar were collected in Rio de Janeiro High levels of immune complexes (IC) were detected in serum by means of 125I-Clq and conglutinin binding assays The Clq binding material had a sedimentation coefficient of 19-25S, as determined by ultracentrifugation on sucrose gradient Plasma levels of C3 and C3 breakdown products were measured and the C3d levels were increased in six out of 11 patients The occurrence of polyclonal B cell activation was suggested by (a) a marked increase of serum IgG and IgM levels and (b) of the presence of antibodies against various proteins and haptens (SRBC, DNP-BSA, FITC-BSA,KLH) There was a close association between the presence of IC and anti-immunoglobulin antibodies Anti-smooth muscle antibodies were also observed These data are consistent with a major role of polyclonal B cell activation in the induction of IC during visceral leishmaniasis

Polyclonal B cell activation, circulating immune complexes and autoimmunity in human american visceral leishmaniasis.

The notion that the pathology of Chagas’ disease has an autoimmune component was initially based on the finding of circulating antibodies binding heart tissue antigens in patients and mice chronically infected with Trypanosoma cruzi. Later, T lymphocytes reactive with heart or nerve tissue antigens were found in chagasic mice and patients, extending the concept to include cell-mediated immunity. However, there is disagreement about whether the observed immunologic autoreactivities are triggered by T. cruzi epitopes and then affect host tissue antigens by virtue of molecular mimicry or are elicited by host antigens exposed to lymphocytes after tissue damage caused by the parasite. There is also disagreement about the relevance of immunologic autoreactivities to the pathogenesis of Chagas’ disease because of the lack of reproducibility of some key reports supporting the autoimmunity hypothesis, conflicting data from independent laboratories, conclusions invalidated by advances in our understanding of the immunologic mechanisms underlying cell lysis, and, last but not least, a lack of direct, incontrovertible evidence that cross-reacting antibodies or autoreactive cells mediate the typical pathologic changes associated with human Chagas’ disease. The data and views backing and questioning the autoimmunity hypothesis for Chagas’ disease are summarized in this review.

https://cmr.asm.org/content/cmr/12/2/210.full.pdf

Chagas’ Disease and the Autoimmunity Hypothesis

A microhematocrit concentration method (MH) for immediate diagnosis of Chagas' disease during the acute stage or in congenital cases was standardized. Parasitemia as low as 1,000 parasites per ml was detected, after centrifugation of six 50-microliters capillary tubes, by 10-min microscopic observation of each buffy coat spread between slide and cover glass. Operator's time was reduced by at least one-third when compared with a fresh blood observation (FB). In 12 of the 15 patients studied, diagnosis was performed in 4.9 +/- 3.08 min with MH, whereas 27.0 +/- 12.1 min were necessary when FB was used. In the three remaining patients whose FB results were negative, MH became positive after 13, 16, and 40 min. In our experience, FB proved to be more sensitive than previously reported. Suckling mouse inoculation also proved to be sensitive but, as in xenodiagnosis and in hemoculture, the delay in getting the final result was a limiting factor.

https://jcm.asm.org/content/jcm/18/2/327.full.pdf

Direct micromethod for diagnosis of acute and congenital Chagas' disease.

The effect of human-specific antibody on surface membrane antigens of trypomastigotes of Trypanosoma cruzi was studied in vitro by using immunofluorescence methods. Immune sera induced aggregation of surface antigens in trypomastigotes to form polar cell caps.

Induction of capping in blood-stage trypomastigotes of Trypanosoma cruzi by human anti-Trypanosoma cruzi antibodies.

Immunologic and immunopathologic studies in congenital Chagas' disease.

Anti-Trypanosoma cruzi agglutinins were studied by the direct agglutination test (DA) with or without previous treatment of the sera with 2-mercaptoethanol (2-ME) (DA and 2-MEDA, respectively), in serial serum samples obtained from 24 patients with acute Chagas' disease. Their agglutinin titers were compared with those found in 25 patients of similar age with other acute infections and 50 healthy children. All of the controls were negative by complement-fixation test for T. cruzi infection. All sera were also tested by indirect hemagglutination (IHA) and indirect immunofluorescence (IIF) tests, using anti-total human globulin (IIF-Ig) and anti-IgM human globulin (IIF-IgM). In the first serum sample obtained after infection from the chagasic patients, DA and 2-MEDA detected IgM antibodies in seven patients who were also positive by IIF-IgM. However, in 13 early sera from other patients antibodies were demonstrated by IIF-IgM only. Four patients were negative by both techniques. Early serum samples were usually negative in the IHA test. Further samples obtained from those patients in whom the infection became chronic were reactive in the IHA test. In these sera, agglutinin titers were usually not affected by 2-ME treatment, indicating a change in the class of Ig reactivity (from IgM to IgG). This observation was coincident with decreasing titers established by IIF-IgM, whereas antibody titers detected by IIF-Ig remained positive. However, in four patients IIF-IgM antibodies either persisted or reappeared following a period during which they were negative. During the follow-up of four patients in whom serologic reactivity became negative after treatment, antibodies were detected later. In two of these cases a positive IIF-IgM was observed.

Anti-Trypanosoma cruzi agglutinins in acute human Chagas' disease.

Trypanosoma cruzi: Antibody-induced mobility of surface antigens

Immunoglobulin M, G, and A concentrations were studied by radial immunodiffusion technique in 16 individuals (two were 16 and 14 yr of age, respectively, while the remaining 14 were 12 yr of age or less) with acute Trypanosoma cruzi infection. Serum samples were obtained from these patients beginning with the onset of symptoms and continuing until several months after treatment with nifurtimox was completed. Soon after infection the concentration of IgM was higher than the average found in healthy children. Some of the samples also had higher values than those found in children with other acute infections. At this time isolated increases in IgG and/or IgA concentrations were also found in T. cruzi-infected patients. Immunoglobulin concentrations had usually returned to normal when treatment with nifurtimox was completed, both in the patients with negative serology and in those who remained positive. However, some of the sera showed isolated higher IgM, IgG, and/or IgA values than those found in healthy controls.

Ana Szarfman

Papers

Induction of capping in blood-stage trypomastigotes of Trypanosoma cruzi by human anti-Trypanosoma cruzi antibodies.

Immunologic and immunopathologic studies in congenital Chagas' disease.

Anti-Trypanosoma cruzi agglutinins in acute human Chagas' disease.

Trypanosoma cruzi: Antibody-induced mobility of surface antigens

Immunoglobulin Concentration in Treated Human Acute Chagas' Disease: A Follow-up Study