Trypanosoma cruzi: immune response in mice immunized with parasite antigens

CpG DNA as a Th1-promoting adjuvant in immunization against Trypanosoma cruzi

Th1-type immune response plays a critical role in resistance to Trypanosoma cruzi infection. We asked whether a synthetic oligodeoxynucleotide that contains immunostimulatory CpG motifs (CpG ODN), known to promote a Th1 response, could act as an adjuvant in immunization with parasite antigens. Mice immunized with a whole homogenate (WH) of T. cruzi antigens co-administered with CpG ODN presented high titers of T. cruzi antibodies (IgG2a isotype), strong delayed type hypersensitivity and a Th1-dominated (IFN-gamma and IL-12) cytokine profile. Furthermore, WH plus CpG ODN protected mice from challenge with an otherwise lethal dose of bloodstream trypomastigotes. As reported for leishmaniasis and malaria, CpG ODN holds considerable promise as an adjuvant for future vaccines against T. cruzi.

Trypanosoma cruzi: protective response of vaccinated mice is mediated by CD8+ cells, prevents signs of polyclonal T lymphocyte activation, and allows restoration of a resting immune state after challenge

Currently, there is no vaccine available against Chagas' disease. Immune abnormalities induced by T. cruzi pose particular difficulties for vaccine development, since immunological memory must be able to overcome them to prevent spread of infection/sequelae. We have previously demonstrated that experimental vaccination with live CL-14 trypomastigotes does not induce polyclonal lymphocyte activation, immunosuppression, or pathology and efficiently immunizes against virulent T. cruzi. Herein we show that: (1) expansion of CD4+ and CD8+ subsets peaks 2 weeks after infective challenge in both challenged-vaccinated mice and infected controls, but the former exhibit a smaller increase in blastogenesis and in the numbers of activated CD11a(hi)CD4+ and CD11a(hi)CD8+ cells; (2) in long-term-vaccinated mice, expansion of activated subsets (CD62Llo/- and CD11a(hi)) is accelerated among CD8+ PBL 1 week after challenge; (3) challenged-vaccinated mice retract the CD8+-activated subset 5 weeks after challenge, different from infected controls; (4) protection conferred by CL-14 immunization can be adoptively transferred to naïve recipients with lymphocyte suspensions, and prior depletion of CD8+ (but not of CD4+) cells abolishes protective immunity. Our findings indicate that protective immunity generated by CL-14 immunization involves a transient CD8+ recall response and is capable of preventing the signs of polyclonal lymphocyte activation induced by virulent challenge.

The relative contribution of antibody production and CD8+ T cell function to immune control of Trypanosoma cruzi

The life cycle of the protozoan parasite Trypanosoma cruzi in mammalian hosts includes both non-dividing trypomastigote forms which circulate in the blood and replicating intracellular amastigotes which reside within the cytoplasm of a variety of host cells. In this study we have used mice with induced mutations in genes responsible for either antibody production or cytolytic T lymphocyte (CTL) function to examine the relative contributions of these effector mechanisms to control of T. cruzi. Mice deficient in the production of antibodies exhibited a delay in the rise in acute phase parasitaemia and an extended time to death relative to mice lacking CD8+ T cells. Nevertheless, B cell deficient mice eventually succumbed to the infection. Prior infection with an avirulent strain of T. cruzi failed to protect either CD8+ T cell-deficient mice or B cell deficient mice from challenge infection with virulent parasites. In contrast, mice with disruptions in the genes controlling perforin- or granzyme B-mediated cytolytic pathways had parasitaemia and mortality rates similar to wild-type mice and were protected from secondary infection by prior exposure to avirulent parasites. These results 1) confirm that antibody production, although secondary in importance to cellular responses, is nevertheless absolutely required and 2) perforin- or granzyme B-mediated lytic pathways are not required for control of T. cruzi infection.

Trypanosoma cruzi: the major cysteinyl proteinase (cruzipain) is a relevant immunogen of parasite acidic antigens (FIII)

This study examined the immune responses induced by cruzipain, a well-characterized T. cruzi antigen, to determine whether it is a relevant immunogen among the parasite acidic antigens (FIII), for which some biological properties have been studied previously. Humoral and cellular immune responses were investigated in BALB/C mice after immunization with cruzipain or FIII. Skin tests revealed immediate type-hypersensitivity (ITH) and delayed-type hypersensitivity (DTH) reactions to cruzipain in both groups of immunized mice. IgG1 and IgE isotypes against cruzipain were detected by ELISA in both groups and immunoblot studies showed that these antibodies recognized a major protein band of 50 kDa, cruzipain. The antigen-specific proliferative responses of spleen lymphocytes from both groups of immunized mice were also increased. Immunization with cruzipain of FIII antigen significantly enhanced the percentage survival of mice challenged with 10(3) trypomastigotes. The results revealed high cross-reactivity between cruzipain and FIII, suggesting the cruzipain is a relevant immunogen among the parasite acidic antigens.

Age-associated changes in lymphoid and antigen-presenting cell functions in mice immunized with Trypanosoma cruzi antigens

The purpose of these studies was to analyze the role of different immune cell populations in the immune response against Trypanosoma cruzi antigens in aged mice. Mice of different ages (3 and 12 months old) were immunized i.d. with S-105 plus Bordetella pertussis as adjuvant and we compared the activities of the lymph node cells taken from 3- and 12-month-old donor animals to transfer DTH or antibody production to 3-month-old recipients. This study revealed that adherent and non-adherent immune lymph node cells of aged donor animals did not transfer response against the foreign antigen (S-105) whereas 3-month-old non-adherent lymph node cells transferred a DTH response as well as helped the specific antibody production. When total lymph node cells from 3- and 12-month-old mice were mixed, we observed an inhibition of S-105 transferred response indicating a suppressive effect of aged cells on the 3-month-old mice cells. Furthermore, we analyzed the participation of antigen-presenting cells (APC) in the immune response changes related to the previously described aged mice. Peritoneal cavities cells (PC), pulsed in vivo with S-105, obtained from 3- and 12-month-old mice were transferred to normal recipients and a DTH response to S-105 was studied. We observed that the DTH response was lower in the recipients of aged PC with respect to recipients of young PC. The results suggest that APC from aged mice are involved in controlling the cellular immune response to S-105. Age-related changes in immune T cell and APC are discussed in the context of these observations.

Enhancement of natural antibodies in mice immunized with exoantigens of pI 4.5 from Trypanosoma cruzi

This paper deals with the enhancement of natural antibodies in mice immunized with a previously purified exoantigen of Trypanosoma cruzi from infected mouse plasma by isoelectric focusing, called Ea 4.5. A simultaneous rinse of IgG antibodies recognizing acidic sciatic nerve antigen (SNA) and other conserved antigens such as myoglobin, actin, thyroglobulin, and tubulin was observed. The highest level of antibodies was revealed when myoglobin was used as antigen in the ELISA test. Good correlation was found between the level of antibodies reactive with SNA and with highly conserved antigens. Furthermore, absorption experiments showed that a fraction of antibodies binding SNA are polyreactive and also react with the highly conserved antigens. The histological studies of sciatic nerve, heart and skeletal muscle performed 1 month after the last immunization revealed no modifications with respect to the control animals. Based on these and a previous result [1], indicating that injection of Ea 4.5 induced in mice a partial protection against T. cruzi, the possibility exists that a percentage of antibodies induced by Ea 4.5 may correspond to the natural autoantibody type and take part in protective and/or pathogenic effects.

Aging: the cellular immune response against autologous and foreign antigens is affected before the humoral response

In this study we examined the auto- and hetero-immune response in mice of different ages immunized with antigens of Trypanosoma cruzi (S-105). We observed that 20-day- and 12-month-old mice showed decreased response to foreign antigens and increased response to autoantigens, compared with 3-month-old immunized mice. The 6-month-old mice showed hetero- and auto-immune cellular responses similar to those of 12-month-old animals; however, the humoral response was similar to that of 3-month-old animals against either antigen, suggesting that the compartments of the immune response are altered at different moments in the same individual. Immune response against a foreign antigen is correlated with the presence of cellular infiltrate in skeletal and heart muscle whereas no modifications in the tissue are noticed in animals with an autoimmune response. Also, we observed from cell transfer experiments that lymph node cells are involved in the dysregulation that we noticed with aging.

Trypanosoma cruzi glutathione-binding proteins (TcGBP): protection induced by native proteins in an experimental model and analysis of the antibody response

Three Trypanosoma cruzi glutathione-binding proteins (TcGBP) of 45, 30 and 25 kDa presenting glutathione S transferase activity were characterized from T. cruzi epimastigotes. We show here that immunization of mice using TcGBP and complete Freund's adjuvant (CFA) did not protect the animals against a challenge with bloodstream trypomastigotes. In contrast, immunization of mice using TcGBP in association with Bordetella pertussis plus alum (BpAI) resulted in greatly diminished parasitaemia and significantly protected the animals from lethal infection. Using TcGBP mixed with BpAI and a lower challenge dose, we obtained strongly diminished parasitaemia and 100% protection in terms of survival. Only sera from mice immunized with TcGBP plus BpAI were able to kill trypomastigotes by complement-mediated lysis, whereas sera from mice immunized with TcGBP plus CFA did not. Interestingly, sera from mice immunized with TcGBP plus BpAI showed significant levels of specific IgE, IgG2a and IgG2b antibodies, whereas these isotypes were not detected in sera from mice immunized with TcGBP in CFA. All these levels were increased in sera of protected animals. These results demonstrate that TcGBP antigens can confer resistance to T. cruzi acute infection in mice, and suggest a possible functional role for both IgE and IgG2 isotypes in the induction of protective immunity.

Immune response in mice immunized with acidic antigenic fractions from Trypanosoma cruzi cytosol

The humoral and cellular immune responses as well as the resistance to infection with bloodstream forms of T. cruzi were studied in mice immunized with acidic antigenic fractions from parasite cytosol, F III and F IV, plus Bordetella pertussis as adjuvant. The immunization with F III induced positive ITH and DTH responses to homologous antigens. In mice immunized with F IV, the ITH was negative and four out of six animals presented positive DTH reactions. In both groups of mice the analysis of IgG against T. cruzi showed that the major isotype elicited was IgG1. Specific IgE was also detected in sera from F III immunized mice, thus confirming the presence of homocytotropic antibodies. The parasitemias reached by F III and F IV immunized mice after challenge were lower than those of the controls showing in this way a partial protection against the acute infection. The histological studies of heart and skeletal muscle performed two months after the infection revealed variable mononuclear infiltration in all infected mice despite immunization.

Trypanosoma cruzi: involvement of IgG isotypes in the parasitemia control of mice immunized with parasite exoantigens of isoelectric point 4.5

In a previous work we demonstrated that Trypanosoma cruzi exoantigens of pI 4.5 (Ea 4.5), whose most important epitopes are glucidic, are able to induce a partially protective immune response in mice. To ascertain the involvement of antibody isotypes in this protection, we immunized mice with Ea 4.5 plus Bordetella pertussis as adjuvant. The analysis of immune response by skin test revealed the occurrence of specific immediate type hypersensitivity on Day 15 after the last immunization. By ELISA and using Ea 4.5 as antigen, specific IgG1 antibody was detected. When formaldehyde-fixed epimastigotes were used as antigen, binding of IgG1 and IgG2 was observed. Trypomastigotes incubated for 1 hr at 33 degrees C with the immune sera and then injected in normal syngeneic mice produced a significantly lower parasitemia than trypomastigotes incubated with the control sera. This capacity of anti-Ea 4.5 sera was resistant to 56 degrees C for 2 hr and was diminished after the absorption of immune sera with the carbohydrate moiety of Ea 4.5. The assay with the immune IgG1 and IgG2, separated through protein A-Sepharose affinity chromatography, showed that IgG1 retains most of this capacity. Purified immune IgG1 revealed two antigenic bands of molecular weight between 50 and 55 kDa in SDS-PAGE of Ea 4.5.

Trypanosoma cruzi: properties of a clone isolated from CL strain

BALB/c mice injected i.p. with 2 x 10(6) metacyclic forms of CL-14, a clone isolated from the CL strain of Trypanosoma cruzi, did not show parasitemia as evaluated by direct blood microscopy examination, hemoculture and xenodiagnosis. Moreover, new-born mice (1-2 days old) injected with culture- or insect-derived CL-14 trypomastigotes also displayed negative parasitemia. No mortality was observed in either group of animals. However, despite this apparent non-infectivity, mice injected with clone 14 developed high resistance against a lethal challenge with virulent trypomastigotes. All challenged mice survived and the parasitemia was negative. These results indicate that clone 14 is a very good antigen for the study of acquired immunity in T. cruzi infection and, therefore, a potential candidate for the development of a vaccine against this parasite.

Trypanosoma cruzi: cellular and antibody response against the parasite in mice immunized with a 19-amino acid synthetic peptide

Several monoclonal antibodies were prepared against the flagellar fraction of Trypanosoma cruzi epimastigotes (Tulahuén strain, stock Tul 2). One of them, FCH-F8-4, has previously shown biologic activity against the parasite (complement-mediated lysis and neutralization of the trypomastigote infectivity). Immunopurified antigens using this monoclonal antibody elicited a protective immune response in mice. Two recombinant cDNA clones were detected with this anti-flagellar fraction monoclonal antibody on a lambda gt11 expression library prepared from T. cruzi epimastigote mRNA. The insert of one of these cDNA clones, lambda(FCH-F8-4)1 (150 bp) coded for a 19-amino acid peptide (PAFLGCSSRFSGSFSGVEP). This insert hybridized with a 5.0-kb mRNA from epimastigotes. The beta-galactosidase fusion protein was produced in lysogenic bacteria. The monoclonal antibody recognized the epitope present in the fusion protein after western blotting of the crude lysate. A synthetic peptide (SP4) containing the complete sequence of lambda(FCH-F8-4)1 was constructed on solid phase. This peptide was able to inhibit the ELISA reactivity (in a range from 13 to 52%) of flagellar fraction immunized mouse sera and when administered (coupled to KLH or alone) to BALB/c mice with Bordetella pertussis as adjuvant, it induced a humoral and cellular immune response which was detected by ELISA, immunofluorescence, blotting, and DTH reactions against T. cruzi antigens. The immune response obtained indicates that this synthetic peptide resembles the parasite antigen conformation and could be useful for diagnosis purposes or be able to elicit immunoprotection against T. cruzi infection.

Increased production of reactive oxygen species by cells from mice acutely infected with Trypanosoma cruzi

Release of reactive oxygen species (ROS) by cells from BALB/c mice was studied during the acute stage of the infection with 50 bloodstream forms of Trypanosoma cruzi, Tulahuén strain. Production of ROS by spleen and peritoneal cells was evaluated by chemiluminescence using luminol as enhancer (CL-Lum). Three to four weeks after infection, CL-Lum response after the addition of opsonized zymosan to spleen and peritoneal cells from infected mice was 13 and 98 times, respectively, above the levels obtained with cells from noninfected mice. The kinetics of this hyperactivity was similar to that of the parasitemia. Both reached maximal values on the third to fourth weeks and decreased at 7 weeks postinfection. During this hyperactivation stage, spleen and peritoneal cells from infected mice showed a "spontaneous" CL-Lum response (without any stimulus added in vitro) absent in noninfected mice. Both, "spontaneous" and zymosan stimulated CL-Lum responses were inhibited by 100 microM azide and by 0.8 microM superoxide dismutase, suggesting the involvement of hemoproteins and superoxide anion in the measured responses. Moreover, spleen cells from acutely infected mice displayed a hyperactivity in the CL-Lum response when recombinant interferon-gamma was added in vitro. Supernatants of spleen cells from both normal or infected mice, stimulated in vitro with concanavalin A, contained similar levels of interferon and were equally able to stimulate the trypanocidal activity of normal macrophages. These results suggest that mediators of activation of phagocytic cells can be produced during acute T. cruzi infection. In addition, phagocytic cells from acutely infected mice were activated in vivo and were hyperactive to the in vitro stimulation.

Expression in Escherichia coli of a dominant immunogen of Trypanosoma cruzi recognized by human chagasic sera

A genomic clone expressing a Trypanosoma cruzi antigen in Escherichia coli was identified using human chagasic sera. Chagasic antibodies affinity purified on extracts of this clone recognized a high-molecular-weight protein expressed in all developmental stages of the parasite life cycle, as well as in various T. cruzi strains. The antigen is associated with the cytoskeleton of the parasite and localizes along the attachment region between the flagellum and the cell body. Antibodies to the recombinant antigen were detected in the sera of 115 chagasic patients from different endemic regions, but not in sera of patients with leishmaniasis, T. rangeli infection, or other parasitic diseases. Our data suggest that the presence of antibodies to this antigen may be specifically associated with Chagas' disease.

Trypanosoma cruzi: quantification in tissues of experimentally infected mice by limiting dilution analysis

A limiting dilution assay (LDA) was developed for the quantification of Trypanosoma cruzi in the heart and blood of infected mice. Three groups of swiss mice were injected ip with "CL", "Colombiana," and "Y" strains. At 1-day intervals after infection, blood and the heart were removed. Serial blood dilutions in LIT medium were performed and distributed in four groups of 24 microplate wells. The growth of parasite was visually checked in an inverted microscope. It was found that curves of parasitemia obtained by parasite counting in a hemocytometer or estimated by LDA were similar. A similar method was used to quantify parasites in the heart of mice. The heart was cut, washed, dried, and its weight was determined. The heart pieces were disrupted by passage through a mesh stainless-steel screen into LIT. Serial dilutions of the heart homogenate were made in LIT and added to at least 24 replicate microplate wells. Parasites were detectable earlier in the heart of mouse infected with Y strain when compared to CL and Colombiana strains. Parasites were detected in the heart of mice of all strains by 6 days after infection. This LDA for quantification of T. cruzi permits a more precise evaluation of the number of living parasites in infected tissues.