RESUMO
Phagocytic removal of apoptotic lymphocytes exacerbates replication of Trypanosoma cruzi in macrophages. We investigated the presence of Ab against apoptotic lymphocytes in T. cruzi infection and the role of these Ab in parasite replication. Both control and chagasic serum contained IgG Ab that opsonized apoptotic lymphocytes. Treatment of apoptotic lymphocytes with purified IgG from chagasic, but not control serum, reduced T. cruzi replication in macrophages. The protective effect of chagasic IgG depended on Fcgamma receptors, as demonstrated by the requirement for the intact Fc portion of IgG, and the effect could be abrogated by treating macrophages with an anti-CD16/CD32 Fab fragment. Chagasic IgG displayed increased reactivity against a subset of apoptotic cell Ag, as measured by flow cytometry and immunoblot analyses. Apoptotic lymphocytes treated with chagasic IgG, but not control IgG, increased production of TNF-alpha, while decreasing production of TGF-beta1 by infected macrophages. Increased control of parasite replication required TNF-alpha production. Previous immunization with apoptotic cells or injection of apoptotic cells opsonized with chagasic IgG reduced parasitemia in infected mice. These results indicate that Ab raised against apoptotic cells could play a protective role in control of T. cruzi replication by macrophages.
Assuntos
Anticorpos Antiprotozoários/imunologia , Doença de Chagas/imunologia , Linfócitos/imunologia , Macrófagos/imunologia , Trypanosoma cruzi/imunologia , Fator de Necrose Tumoral alfa/metabolismo , Transferência Adotiva , Animais , Anticorpos Antiprotozoários/farmacologia , Apoptose , Células Cultivadas , Doença de Chagas/parasitologia , Doença de Chagas/terapia , Técnicas de Cocultura , Citometria de Fluxo , Immunoblotting , Imunoglobulina G/imunologia , Imunoglobulina G/farmacologia , Linfócitos/citologia , Linfócitos/efeitos dos fármacos , Macrófagos/citologia , Macrófagos/parasitologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Parasitemia/imunologia , Parasitemia/parasitologia , Parasitemia/terapia , Fagocitose , Fator de Crescimento Transformador beta1/metabolismo , Trypanosoma cruzi/efeitos dos fármacos , Trypanosoma cruzi/crescimento & desenvolvimentoRESUMO
Caspases are cysteine aspartases acting either as initiators (caspases 8, 9, and 10) or executioners (caspases 3, 6, and 7) to induce programmed cell death by apoptosis. Parasite infections by certain intracellular protozoans increase host cell life span by targeting caspase activation. Conversely, caspase activation, followed by apoptosis of lymphocytes and other cells, prevents effective immune responses to chronic parasite infection. Here we discuss how pharmacological inhibition of caspases might affect the immunity to protozoan infections, by either blocking or delaying apoptosis.
Assuntos
Antiprotozoários/uso terapêutico , Apoptose/efeitos dos fármacos , Inibidores de Caspase , Infecções por Protozoários/tratamento farmacológico , Animais , Antiprotozoários/imunologia , Apoptose/imunologia , Humanos , Tolerância Imunológica/efeitos dos fármacos , Camundongos , Infecções por Protozoários/enzimologia , Infecções por Protozoários/imunologia , Receptores de Morte Celular/imunologiaRESUMO
Infection with Trypanosoma cruzi causes expansion of subcutaneous (SLN) and atrophy of mesenteric (MLN) lymph nodes. Here we show that excision of MLN increased parasitemia in T. cruzi-infected mice. We then studied how apoptosis of MLN cells affects immune responses to infection. T cell apoptosis increased in the MLN compared to SLN in T. cruzi-infected mice. Absolute numbers of naïve T cells decreased, and activated T cells failed to accumulate in MLN during infection. In addition, activated T cells from MLN produced less IL-2, IFN-gamma, IL-4, and IL-10 than T cells from SLN. Treatment with IL-4 or with caspase-9 inhibitor increased the recovery of viable T cells in vitro. Treatment with caspase-9 inhibitor also increased the production of cytokines by MLN T cells from infected mice. Moreover, injection of a pan caspase inhibitor prevented MLN atrophy during T. cruzi infection. Caspase-9, but not caspase-8, inhibitor also reduced MLN atrophy and increased the recovery of naïve and activated T cells from MLN. These findings indicate that caspase-mediated apoptosis and defective cytokine production are implicated in MLN atrophy and affect immune responses to T. cruzi infection.
Assuntos
Apoptose/imunologia , Doença de Chagas/imunologia , Linfonodos/imunologia , Mesentério/imunologia , Pele/imunologia , Linfócitos T/imunologia , Animais , Atrofia , Caspases/efeitos dos fármacos , Caspases/imunologia , Caspases/metabolismo , Citocinas/biossíntese , Inibidores Enzimáticos/farmacologia , Ensaio de Imunoadsorção Enzimática , Citometria de Fluxo , Linfonodos/microbiologia , Linfonodos/patologia , Ativação Linfocitária/imunologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Linfócitos T/microbiologia , Linfócitos T/patologia , Trypanosoma cruziRESUMO
Caspases, a family of cysteinyl-aspartate-specific proteases, induce apoptosis but are also involved in signal transduction in live cells. Caspase activation and apoptosis in T lymphocytes occur following infection with parasites and might affect immune responses. Rapid progress has occurred in the development and testing of caspase inhibitors and other apoptosis blockers, which are potentially useful for treating diseases associated with the pathogenic effects of apoptosis. Pharmacological approaches and the use of genetically modified hosts can be combined in research strategies to understand how apoptosis and caspase signaling affect the immune system.
Assuntos
Caspases/fisiologia , Doença de Chagas/imunologia , Transdução de Sinais/fisiologia , Animais , Apoptose , Doença de Chagas/patologia , Citocinas/fisiologia , Humanos , Imunidade Inata , Ativação Linfocitária , Macrófagos/fisiologia , Linfócitos T/imunologiaRESUMO
We investigated the role of the Fas ligand (FasL)/Fas death pathway on apoptosis and cytokine production by T cells in Trypanosoma cruzi infection. Anti-FasL, but not anti-TNF-alpha or anti-TRAIL, blocked activation-induced cell death of CD8 T cells and increased secretion of IL-10 and IL-4 by CD4 T cells from T. cruzi-infected mice. CD4 and CD8 T cells up-regulated Fas/FasL expression during T. cruzi infection. However, Fas expression increased earlier in CD8 T cells, and a higher proportion of CD8 T cells was activated and expressed IFN-gamma compared with CD4 T cells. Injection of anti-FasL in infected mice reduced parasitemia and CD8 T cell apoptosis and increased the ratio of CD8:CD4 T cells recovered from spleen and peritoneum. FasL blockade increased the number of activated T cells, enhanced NO production, and reduced parasite loads in peritoneal macrophages. Injection of anti-FasL increased IFN-gamma secretion by splenocytes responding to T. cruzi antigens but also exacerbated production of type 2 cytokines IL-10 and IL-4 at a late stage of acute infection. These results indicate that the FasL/Fas death pathway regulates apoptosis and coordinated cytokine responses by type 1 CD8 and type 2 CD4 T cells in T. cruzi infection.
Assuntos
Linfócitos T CD4-Positivos/metabolismo , Linfócitos T CD8-Positivos/metabolismo , Doença de Chagas/imunologia , Transdução de Sinais , Receptor fas/metabolismo , Animais , Apoptose , Linfócitos T CD4-Positivos/fisiologia , Linfócitos T CD8-Positivos/fisiologia , Proliferação de Células , Doença de Chagas/metabolismo , Citocinas/metabolismo , Proteína Ligante Fas/metabolismo , Imunidade Celular , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Modelos Imunológicos , Regulação para CimaRESUMO
Viral FLIPs (vFLIPs) interfere with apoptosis signaling by death-domain-containing receptors in the TNFR superfamily (death receptors). In this study, we show that T cell-specific transgenic expression of MC159-vFLIP from the human Molluscum contagiosum virus blocks CD95-induced apoptosis in thymocytes and peripheral T cells, but also impairs postactivation survival of in vitro activated primary T cells despite normal early activation parameters. MC159 vFLIP impairs T cell development to a lesser extent than does Fas-associated death domain protein deficiency or another viral FLIP, E8. In the periphery, vFLIP expression leads to a specific deficit of functional memory CD8(+) T cells. After immunization with a protein Ag, Ag-specific CD8(+) T cells initially proliferate, but quickly disappear and fail to produce Ag-specific memory CD8(+) T cells. Viral FLIP transgenic mice exhibit impaired CD8(+) T cell responses to lymphocytic choriomeningitis virus and Trypanosoma cruzi infections, and a specific defect in CD8(+) T cell recall responses to influenza virus was seen. These results suggest that vFLIP expression in T cells blocks signals necessary for the sustained survival of CD8(+) T cells and the generation of CD8(+) T cell memory. Through this mechanism, vFLIP proteins expressed by T cell tropic viruses may impair the CD8(+) T cell immune responses directed against them.