RESUMO
We investigated how apoptosis pathways mediated by death receptors and caspase-8 affect cytokine responses and immunity to Leishmania major parasites. Splenic CD4 T cells undergo activation-induced apoptosis, and blockade of FasL-Fas interaction increased IFN-γ and IL-4 cytokine responses to L. major antigens. To block death receptor-induced death, we used mice expressing a T cell-restricted transgene for vFLIP. Inhibition of caspase-8 activation in vFLIP mice enhanced Th1 and Th2 cytokine responses to L. major infection, even in the Th1-prone B6 background. We also observed increased NO production by splenocytes from vFLIP mice upon T cell activation. Despite an exacerbated Th2 response, vFLIP mice controlled better L. major infection, with reduced lesions and lower parasite loads compared with WT mice. Moreover, injection of anti-IL-4 mAb in infected vFLIP mice disrupted control of parasite infection. Therefore, blockade of caspase-8 activity in T cells improves immunity to L. major infection by promoting increased Th1 and Th2 responses.
Assuntos
Caspase 8/metabolismo , Imunidade Celular/imunologia , Leishmania major/imunologia , Leishmaniose/imunologia , Leishmaniose/prevenção & controle , Células Th1/imunologia , Células Th2/imunologia , Animais , Antígenos de Protozoários/imunologia , Apoptose , Feminino , Humanos , Interleucina-4/metabolismo , Leishmaniose/parasitologia , Ativação Linfocitária/imunologia , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas Virais/imunologiaRESUMO
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
In experimental Chagas' disease, lymphocytes from mice infected with Trypanosoma cruzi show increased apoptosis in vivo and in vitro. Treatment with a pan-caspase blocker peptide inhibited expression of the active form of effector caspase-3 in vitro and rescued both B and T cells from cell death. Injection of the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethyl ketone, but not a control peptide, reduced parasitemia and lymphocyte apoptosis in T. cruzi-infected mice. Moreover, treatment with caspase inhibitor throughout acute infection increased the absolute numbers of B and T cells in the spleen and lymph nodes, without affecting cell infiltrates in the heart. Following treatment, we found increased accumulation of memory/activated CD4 and CD8 T cells, and secretion of IFN-gamma by splenocytes stimulated with T. cruzi antigens. Caspase inhibition in the course of infection reduced the intracellular load of parasites in peritoneal macrophages, and increased the production of TNF-alpha and nitric oxide upon activation in vitro. Our results indicate that inhibition of caspases with a pan-caspase blocker peptide improves protective type-1 immune responses to T. cruzi infection. We suggest that mechanisms of apoptosis are potential therapeutic targets in Chagas' disease.
Assuntos
Apoptose/imunologia , Inibidores de Caspase , Doença de Chagas/imunologia , Doença de Chagas/patologia , Linfócitos/enzimologia , Trypanosoma cruzi/imunologia , Clorometilcetonas de Aminoácidos/farmacologia , Animais , Apoptose/efeitos dos fármacos , Doença de Chagas/tratamento farmacológico , Doença de Chagas/enzimologia , Linfócitos/efeitos dos fármacos , Linfócitos/imunologia , Masculino , Camundongos , Camundongos Endogâmicos BALB CRESUMO
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
During Trypanosoma cruzi infection, T cells up-regulate caspase-8 activity. To assess the role of caspase-8 in T cell-mediated immunity, we investigated the effects of caspase-8 inhibition on T cells in viral FLIP (v-FLIP) transgenic mice. Compared with wild-type controls, increased parasitemia was observed in v-FLIP mice infected with T. cruzi. There was a profound decrease in expansion of both CD4 and CD8 T cell subsets in the spleens of infected v-FLIP mice. We did not find differences in activation ratios of T cells from transgenic or wild-type infected mice. However, the numbers of memory/activated CD4 and CD8 T cells were markedly reduced in v-FLIP mice, possibly due to defective survival. We also found decreased production of IL-2 and increased secretion of type 2 cytokines, IL-4 and IL-10, which could enhance susceptibility to infection. Similar, but less pronounced, alterations were observed in mice treated with the caspase-8 inhibitor, zIETD. Furthermore, blockade of caspase-8 by zIETD in vitro mimicked the effects observed on T. cruzi infection in vivo, affecting the generation of activated/memory T cells and T cell cytokine production. Caspase-8 is also required for NF-kappaB signaling upon T cell activation. Blockade of caspase-8 by either v-FLIP expression or treatment with zIETD peptide decreased NF-kappaB responses to TCR:CD3 engagement in T cell cultures. These results suggest a critical role for caspase-8 in the establishment of T cell memory, cell signaling, and regulation of cytokine responses during protozoan infection.