RESUMO
Highly virulent strains of Trypanosoma cruzi are frequently used as murine models of Chagas' disease. However, these strains do not fully represent the spectrum of parasites involved in the human infection. In this paper, we analysed parasitaemia, mortality, tissue pathology and parasite-specific IgG serum levels in immune-deficient mice infected with Sylvio X10/4 parasites, a T. cruzi derived from a chagasic patient that yields very low parasitaemias and in C3H/HePAS mice induces a chronic cardiopathy resembling the human disease. IFN-gamma was identified as a crucial element for parasite control as its absence determined a drastic increase in parasitaemia, tissue parasitism, leukocyte infiltrates at the heart and striated muscles and mortality. The lack of IFN-gamma or IL-12p40, a molecule shared by IL-12 and IL-23, also resulted in spinal cord lesions and a progressive paralysis syndrome. Whereas IgG2a was the main Ig isotype in infected C57BL/6 mice, IL-12p40-KO mice produced IgG2a and IgG1 and IFN-gamma-KO mice produced only IgG1. The IFN-gamma-protective effect was not essentially mediated by nitric oxide (NO), inasmuch as infected iNOS-KO mice showed no parasitaemia and low tissue damage. Mice deficient in CD4(+) or CD8(+) T cells showed an intermediate phenotype with increased mortality and tissue pathology but no parasitaemia. Interestingly, CD28-KO mice were unable to produce anti-T. cruzi IgG antibodies but presented moderate tissue pathology and managed to control the infection. Thus, differently from infections with high virulence parasites, neither IgG, NO nor CD28-mediated signalling are essential for the non-sterile control of Sylvio X10/4 parasites.
Assuntos
Especificidade de Anticorpos , Cardiomiopatia Chagásica/imunologia , Imunoglobulina G , Interferon gama/fisiologia , Óxido Nítrico , Trypanosoma cruzi/imunologia , Trypanosoma cruzi/patogenicidade , Animais , Linhagem Celular , Cardiomiopatia Chagásica/genética , Cardiomiopatia Chagásica/metabolismo , Modelos Animais de Doenças , Feminino , Imunoglobulina G/fisiologia , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Nus , Óxido Nítrico/fisiologia , Virulência/genética , Virulência/imunologiaRESUMO
Polyclonal B-cell activation is a feature of the early spleen cell response to blood-stage Plasmodium chabaudi malaria. Immunity to blood-stage malaria is guaranteed by the generation of B cells able to produce parasite-specific antibodies mainly from the immunoglobulin (Ig)G2a isotype. In the present study, we characterized the spleen B-cell compartment during blood-stage P. chabaudi infection. The numbers of B220(+) and B220(LOW) CD138(+) (plasma) cells increased sharply between days 4 and 7 post-infection (p.i.). At this time B220(+) cells expressed surface (s)IgM, but nearly all B220(LOW) CD138(+) cells showed concomitantly intracellular (i)IgM and IgG2a. Both follicular and marginal zone B cells were activated expressing high amounts of CD69. At day 40 p.i., B220(LOW) CD138(+) cell population was still increased but, differently from acute infection, 61.1% of these cells were positive for iIgG2a while only 14.2% expressed iIgM. Moreover, at days 20 and 40 p.i., 29.2% and 13.0% of B220(+) cells expressed sIgG2a, respectively. According to cell size and expression of CD80, CD86, CD11b, CD44 and CD38, B220(+) sIgG2a(+) cells had a phenotype characteristic of activated/memory B cells. Furthermore, 14.1% of B220(+) sIgG2a(+) cells at day 30 p.i. expressed a marginal zone B-cell phenotype. Importantly, B cells from 40-day-infected mice were very efficient in presenting parasite antigens leading to proliferation of both CD4(+) and CD8(+) cells. Our results contribute for understanding the dynamics of B cells during P. chabaudi infection, underlying the mechanisms of antigen presentation and antibody production, which are essential for the acquisition of protective immunity against malaria.
Assuntos
Subpopulações de Linfócitos B/imunologia , Malária/imunologia , Malária/parasitologia , Plasmodium chabaudi/imunologia , Baço/imunologia , Animais , Anticorpos Antiprotozoários/biossíntese , Apresentação de Antígeno/imunologia , Subpopulações de Linfócitos B/parasitologia , Subpopulações de Linfócitos B/patologia , Células Cultivadas , Feminino , Imunofenotipagem , Contagem de Linfócitos , Malária/sangue , Camundongos , Camundongos Endogâmicos C57BL , Parasitemia/imunologia , Parasitemia/parasitologia , Parasitemia/patologia , Plasmócitos/imunologia , Plasmócitos/parasitologia , Plasmócitos/patologia , Plasmodium chabaudi/crescimento & desenvolvimento , Baço/citologia , Baço/patologiaRESUMO
Infection by Plasmodium chabaudi results in polyclonal activation, massive proliferation and differentiation of lymphocytes with parasite-unrelated specificities. To verify if polyclonal activation includes experienced B and T lymphocytes and if it modifies pre-established cytokine and Ig-isotype patterns, mice were immunized with ovalbumin (OVA) in alum, a condition that favours T helper 2/immunoglobulin G1 (Th2/IgG1) responses, and infected with P. chabaudi 7 or 80 days later. Polyclonal activation markedly increased the number of anti-OVA Ig-secreting cells in the spleen, an effect more patent in mice infected 7 days after OVA immunization, but also evident in mice infected after 80 days. The Ig-isotype profile predefined by immunization was not qualitatively modified by polyclonal activation. Thus, although P. chabaudi infection preferentially induces IgG2a, the expanded anti-OVA response is dominated by IgG1. Polyclonal expansion of the anti-OVA response did not yield an enlarged memory B-cell pool that could be recalled months later by OVA boosting. Moreover, polyclonal activation of anti-OVA IgG1-secreting cells did not increase this antibody in serum, a probable consequence of the high Ig turnover observed during infection. When OVA-specific T-cell cytokines were evaluated, we observed an increase of both interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) in mice infected 7 days after immunization, whereas in those infected after 80 days, only IL-4 was augmented. These results suggest that polyclonal activation expands experienced B- and T-cell compartments, preserving their antibody and cytokine patterns.
Assuntos
Subpopulações de Linfócitos B/imunologia , Ativação Linfocitária , Ovalbumina/imunologia , Plasmodium chabaudi/imunologia , Subpopulações de Linfócitos T/imunologia , Animais , Anticorpos Antiprotozoários/biossíntese , Anticorpos Antiprotozoários/sangue , Anticorpos Antiprotozoários/imunologia , Células Clonais/imunologia , Feminino , Imunização , Imunização Secundária , Imunoglobulina G/biossíntese , Imunoglobulina G/sangue , Imunoglobulina G/imunologia , Isotipos de Imunoglobulinas/biossíntese , Isotipos de Imunoglobulinas/sangue , Isotipos de Imunoglobulinas/imunologia , Memória Imunológica , Interferon gama/metabolismo , Interleucina-4/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Fatores de TempoRESUMO
The mechanisms by which antibodies interfere with Plasmodium growth are still under debate. Characterizing the asexual erythrocyte stages susceptible to antibodies from hyperimmune individuals is therefore a relevant contribution to vaccine research. In this study, using a virulent and synchronous murine malaria parasite, Plasmodium chabaudi chabaudi AJ, we have shown that trophozoites and circulating schizonts are not the main targets for antibodies from hyperimmune serum. In drug-cured mice challenged with a high inoculum of ring-infected erythrocytes, parasitemias do not decline until the moment of erythrocyte rupture, suggesting that effector mechanisms operate immediately prior to reinvasion. Confirming these findings, treatment of primary-infected mice with hyperimmune serum inhibited the generation of new ring forms, but did not alter the numbers of schizont-infected erythrocytes, despite the fact that these cells were recognized by immunoglobulin (Ig)G antibodies. When these mice were treated with IgG1 or IgG2a purified from hyperimmune serum, both subclasses limited reinvasion, but IgG2a showed a stronger protective activity. The fact that Fc digestion decreases but does not abrogate protection suggests that both Fc-dependent and independent mechanisms participate in this process. Treatment with cobra venom factor did not interfere with the antibody-mediated protection, ruling out the participation of the complement system in both lysis and phagocytosis of merozoites or infected erythrocytes. Therefore, in mice suffering from P. c. chabaudi AJ malaria, merozoite neutralization seems to be a major mechanism of protection conferred by hyperimmune serum antibodies. However, FcgammaR-mediated interactions, or other mechanisms not yet defined, may also contribute to inhibit erythrocyte reinvasion.