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Infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi results in an orchestrated expression of chemokines and chemokine receptors within the heart that coincides with parasite burden and cellular infiltration. CC chemokine receptor 5 (CCR5) is prominently expressed during both acute and chronic disease, suggesting a role in regulating leukocyte trafficking and accumulation within the heart following T. cruzi infection. To better understand the functional role of CCR5 and its ligands with regard to both host defense and/or disease, CCR5(-/-) mice were infected with T. cruzi, and the disease severity was evaluated. Infected CCR5(-/-) mice develop significantly higher levels of parasitemia (P < or = 0.05) and cardiac parasitism (P < or = 0.01) during acute infection that correlated with reduced survival. Further, we show that CCR5 is essential for directing the migration of macrophages and T cells to the heart early in acute infection with T. cruzi. In addition, data are provided demonstrating that CCR5 does not play an essential role in maintaining inflammation in the heart during chronic infection. Collectively, these studies clearly demonstrate that CCR5 contributes to the control of parasite replication and the development of a protective immune response during acute infection but does not ultimately participate in maintaining a chronic inflammatory response within the heart.

The expression of chemokines within the heart during experimental infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi was characterized in an attempt to determine a functional role for these molecules in both host defense and disease. Analysis of chemokine transcripts revealed that CXC chemokine ligand 9 (CXCL9) and CXCL10, as well as CC chemokine ligand 2 (CCL2) and CCL5, were prominently expressed during acute disease, whereas transcripts for CXCL9, CXCL10, and CCL5 remained elevated during chronic infection. Inflammatory macrophages present within the heart were the primary cellular source of these chemokines following T. cruzi infection. Peak chemokine expression levels coincided with increased gamma interferon expression and inflammation within the heart, suggesting a role for these molecules in both host defense and disease. Indeed, simultaneous treatment of T. cruzi-infected mice with neutralizing antibodies specific for CXCL9 and CXCL10 resulted in an increased parasite burden that was sustained out to 50 days p.i. Antibody targeting either CXCL10 or CCL5 did not change either T. cruzi burden within the heart nor attenuate the severity of cardiac inflammation at any time point examined, while targeting CXCL9 in combination with CXCL10 resulted in increased parasite burden. Collectively, these studies imply that CXCL9 and CXCL10 signaling enhances immune responses following parasite infection. However, antibody targeting of CXCL9 and CXCL10, or CXCL10 alone, or CCL5 alone does not directly modulate the inflammatory response within the heart, suggesting that other proinflammatory factors are able to regulate inflammation in this tissue in response to T. cruzi infection.

How chemokines shape the immune response to viral infection of the central nervous system (CNS) has largely been considered within the context of recruitment and activation of antigen-specific lymphocytes. However, chemokines are expressed early following viral infection, suggesting an important role in coordinating innate immune responses. Herein, we evaluated the contributions of CXC chemokine ligand 10 (CXCL10) in promoting innate defense mechanisms following coronavirus infection of the CNS. Intracerebral infection of RAG1(-/-) mice with a recombinant CXCL10-expressing murine coronavirus (mouse hepatitis virus) resulted in protection from disease and increased survival that correlated with a significant increase in recruitment and activation of natural killer (NK) cells within the CNS. Accumulation of NK cells resulted in a reduction in viral titers that was dependent on gamma interferon secretion. These results indicate that CXCL10 expression plays a pivotal role in defense following coronavirus infection of the CNS by enhancing innate immune responses.

Sera and peripheral blood mononuclear cells (PBMC) from patients displaying different clinical symptoms as well as from normal uninfected individuals (NI) were used to evaluate the humoral and cellular responses of Chagas' disease patients to Trypanosoma cruzi-derived paraflagellar rod proteins (PFR). Our results show that sera from both asymptomatic Chagas' disease patients (ACP) and cardiac Chagas' disease patients (CCP) have higher levels of antibodies to PFR than sera from NI. Immunoglobulin G1 (IgG1) and IgG3 were the main Ig isotypes that recognized PFR. We also tested three recombinant forms of PFR, named rPAR-1, rPAR-2, and rPAR-3, by Western blot analysis. Sera from seven out of eight patients with Chagas' disease recognized one of the three rPAR forms. Sera from 75, 50, and 37.5% of Chagas' disease patients tested recognized rPAR-3, rPAR-2, and rPAR-1, respectively. PFR induced proliferation of 100 and 70% of PBMC from ACP and CCP, respectively. Further, stimulation of cells from Chagas' disease patients with PFR enhanced the frequencies of both small and large CD4(+) CD25(+) and CD4(+) CD69(+) lymphocytes, as well as that of small CD8(+) CD25(+) lymphocytes. Finally, we evaluated the ability of PFR to elicit the production of gamma interferon (IFN-gamma) by PBMC from patients with Chagas' disease. Fifty percent of the PBMC from ACP as well as CCP produced IFN-gamma upon stimulation with PFR. PFR enhanced the percentages of IFN-gamma-producing cells in both CD3(+) and CD3(-) populations. Within the T-cell population, large CD4(+) T lymphocytes were the main source of IFN-gamma.

The gene family encoding a trypomastigote-specific protein restricted to the part of the flagellum in contact with the cell body of the trypomastigote form of Trypanosoma cruzi has been isolated, characterized, and expressed in a baculovirus expression system. The gene family contains three tandemly repeated members that have 97 to 100% sequence identity. The predicted protein encoded by the gene family has both significant amino acid sequence identity and other physical and biological features in common with the TolA proteins of Escherichia coli and Pseudomonas aeruginosa. Based on these similarities, we have designated this gene family tolT. Immunization of mice with recombinant TolT generates a population of CD4(+) T lymphocytes that recognize T. cruzi-infected macrophages, resulting in the production of gamma interferon (IFN-gamma), which leads to NO production and a 50 to 60% reduction in parasite numbers compared to that seen with infected macrophages incubated with naive T cells. This population of T cells also produces both IFN-gamma and interleukin 2 (IL-2) but not IL-4 or IL-5 when incubated with spleen cells stimulated with TolT antigen, indicating that they are of the T-helper 1 type. T cells from mice chronically infected with T. cruzi also produce significant levels of IFN-gamma when cocultured with macrophages and either TolT protein or paraflagellar rod protein, indicating that both of these flagellar proteins produce positive T-cell responses in mice chronically infected with T. cruzi.

The paraflagellar rod proteins (PAR) purified from Trypanosoma cruzi epimastigotes were shown to protect mice against an otherwise lethal challenge inoculum of 10(3) bloodstream-form trypomastigotes. The injection route used for immunization was shown to have a marked impact on the development of protective immunity. Mice receiving subcutaneous (s.c.) injections of PAR proteins had reduced bloodstream parasitemias and showed 100% survival following challenge. In contrast, mice immunized via the intraperitoneal (i.p.) route developed parasitemia levels equivalent to those of unimmunized controls and did not survive infection. Western blotting (immunoblotting) demonstrated that sera from both i.p. and s.c. immunized mice reacted specifically with PAR proteins; however, the antibody titer of the i.p. immunized mice was approximately 64-fold greater than that of the s.c. immunized mice, suggesting that the protective response in the s.c. immunized mice is cell mediated rather than humoral.

Monoclonal antibodies reactive with the surface antigens of the Peru strain of Trypanosoma cruzi were analyzed by Western blots and immunofluorescence assays to determine their reactivity with three life cycle stages and five strain isolates of T. cruzi. One monoclonal antibody, 7.6, recognized a 68-kilodalton (kDa) polypeptide in Western blots of Peru strain trypomastigotes, epimastigotes, and amastigotes. A 68-kDa polypeptide was also detected by monoclonal antibody 7.6 in trypomastigotes of the CL and Y strains and in the clonal isolates Esmeraldo clone 3 and Silvio X10 clone 1. Positive immunofluorescence results were obtained for all life cycle stages of the five strains that were reacted with monoclonal antibody 7.6, thus indicating that the antigen recognized by monoclonal antibody 7.6 is universally present in all T. cruzi strains tested. In contrast, monoclonal antibody 4.2 reacted with a polypeptide doublet of 90 and 105 kDa in Western blots of Peru strain trypomastigotes, but it did not detect these antigens in epimastigotes or amastigotes. The same polypeptide doublet of 90 and 105 kDa was also detected in Western blots of Y strain trypomastigotes; however, no bands were detected in blots of strain CL or isolate Silvio X10 clone 1 trypomastigotes. In blots of Esmeraldo clone 3 trypomastigotes, a single band of 130 kDa was detected by monoclonal antibody 4.2. In immunofluorescence assays of monoclonal antibody 4.2, positive reactions were obtained only with trypomastigotes of Peru, Y, and Esmeraldo clone 3 strains. Thus, monoclonal antibody 4.2 recognizes a trypomastigote-specific antigen which is not universally present on all strains of T. cruzi.

In studies of the resistance of inbred mice to infection with Trypanosoma cruzi Peru, mouse strain B10.S was the only strain which survived the infection resulting from the inoculation of 10(3) trypomastigotes. This is the only inbred mouse strain studied to survive infection. To investigate the effect of the H-2 haplotype on survival, C57BL/10 congenic mouse strains bearing H-2S recombinant haplotypes and mouse strains A.SWSn/J and SJL/J were tested for their ability to overcome the T. cruzi infection. None of the recombinant strains tested, including B10.S(7R), B10.S(8R), B10.S(9R), and B10.HTT, survived the infection, indicating that at least two or more regions of the H-2 locus must be H-2S to ensure survival. Strains A.SWSn/J and SJL/J with the H-2S haplotype did not survive, indicating that the genetic background outside the H-2 complex also influences survival. The congenic F1 hybrid (C57BL/10 X B10.S) F1 exhibited intermediate survival levels when compared with the parental strains, indicating that H-2S survival is affected by gene dosage. The F1 hybrid strain [B10.S(7R) X B10.S(8R)]F1, which possesses the complete H-2S haplotype in the trans configuration, did not survive T. cruzi infection, suggesting that H-2S-mediated survival does not operate by trans complementation.