Prevalence of CD8(+)alpha beta T cells in Trypanosoma cruzi-elicited myocarditis is associated with acquisition of CD62L(Low)LFA-1(High)VLA-4(High) activation phenotype and expression of IFN-gamma-inducible adhesion and chemoattractant molecules

The determinants of the prevalence of CD8(+) T cells in the inflamed myocardium of Trypanosoma cruzi-infected patients and experimental animals are undefined. Using C3H/He mice infected with the Colombiana strain of T. cruzi, we found that the distribution of CD4(+)/CD8(-) and CD4(-)/CD8(+) T cells in the myocardium mirrors the frequency of cells expressing the CD62L(Low)LFA-1(High)VLA-4(High) activation phenotype among CD4(+)/CD8(-) and CD4(-)/CD8(+ )peripheral blood T cells. Consistently, vascular cell adhesion molecule-1-positive endothelial cells and a fine fibronectin network surrounding VLA-4(+) mononuclear cells were found in the inflamed myocardium. Further, interferon gamma (IFN-gamma) and IFN-gamma-induced chemokines (RANTES, MIG and CRG-2/IP-10), as well as JE/MCP-1 and MIP1-alpha, were found to be the dominant cytokines expressed in situ during acute and chronic myocarditis elicited by T. cruzi. In contrast, interleukin 4 mRNA was only detected during the chronic phase. Altogether, the results indicate that the distribution of T-cell subsets in the myocardium of T. cruzi-infected mice reflects the particular profile of adhesion molecules acquired by most peripheral CD8(+) T lymphocytes and point to the possibility that multiple IFN-gamma-inducible molecules present in the inflamed tissue contribute to the establishment and maintenance of T. cruzi-induced myocarditis.

Trypanosoma cruzi: lack of T cell abnormalities in mice vaccinated with live trypomastigotes

We have previously shown that inoculation of Trypanosoma cruzi clone-CL-14 generates efficient protective immunity against virulent T. cruzi and no infection or histopathology per se, indicating that it induces an immune state different from that exhibited by infected animals. To understand the basis of this difference, we screened CL-14-vaccinated mice for T cell abnormalities thought to be involved in the genesis of pathology. Lymphocytes from vaccinated mice present normal proliferative responses to concanavalin A; enhanced responses to T. cruzi antigens; do not show evidence of polyclonal activation (increased blast transformation and lymphocyte numbers) or changes in the density of CD4, CD8 and TCR-beta expression. Also, vaccinated mice display transient expansion of CD8+ lymphocytes expressing activated phenotypes (CD11a(hi) CD45RBlo CD62Llo). In view of the absence of pathology in vaccinated animals, the absence of immunosuppression and the restoration of a resting immune state reinforce the benign nature of this immunization.

Chagas' disease encephalitis: intense CD8+ lymphocytic infiltrate is restricted to the acute phase, but is not related to the presence of Trypanosoma cruzi antigens

Central nervous system (CNS) damage can occur during Chagas' disease, especially in children and immunosuppressed patients. During the acute phase, amastigotes are rarely found, but inflammatory infiltrates are scattered throughout the CNS. Moreover, peripheral lymphocytes and antibodies recognizing neural components were described, suggesting the participation of the immune system in the genesis of neural lesions. Herein, we performed a histopathological study of Colombian-infected C3H/He mice, comparing the distribution of CNS-inflammatory infiltrates versus Trypanosoma cruzi antigens. Inflammatory infiltrates were observed during the acute phase, but did not correlate with the presence of detectable T. cruzi antigens. Infiltrates consisted mainly of CD8+ lymphocytes, although macrophages and a few CD4+ cells were observed. In the chronic stage of infection, although neuropathies were a common finding, only mild inflammatory infiltrates could be detected. Our results suggest that the presence of CNS inflammatory infiltrates is not directly related to the presence of parasite antigens and indicate that, different from chronic myocarditis, encephalitis resolves during the acute phase of Chagas' disease.

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.

High expression of a functional cruzipain by a non-infective and non-pathogenic Trypanosoma cruzi clone

We compared a Trypanosoma cruzi clone unable to infect or induce pathology in mice (CL-14), with virulent T. cruzi (Y and CL strains) in terms of cruzipain expression, subcellular distribution and functional activity. Our results showed that (1) intracellular Y amastigotes expressed R1 (carboxy-terminal) and R2 (catalytic) domains concentrated in cytoplasmic vesicles, while CL-14 presented R1 labelling on membrane clusters and R2 in intracellular compartments, (2) CL-14-trypomastigotes presented R1 and R2 staining preferentially on flagellar and cellular membranes, similar to CL, but different from Y strain intracellular labelling pattern, (3) flow-cytometry revealed higher expression of R1 by CL-14-trypomastigotes than virulent strains, but R2 staining similar to CL-trypomastigotes, (4) CL-14-trypomastigotes presented normal cruzipain activity in gelatin gels, but different banding patterns were found in CL-14 versus CL and Y strains. Our data rule out failure in cruzipain expression, activity or subcellular distribution as an explanation for CL-14 biological behaviour, but suggest the expression of a different isoform. These results also cast doubt on the putative role of cruzipain as a target of immunopathological responses, since high levels of functional cruzipain are expressed by a non-pathogenic T. cruzi.