RESUMO
The innate immune system is the first mechanism of vertebrate defense against pathogen infection. In this study, we present evidence for a novel immune evasion mechanism of Trypanosoma cruzi, mediated by host cell plasma membrane-derived vesicles. We found that T. cruzi metacyclic trypomastigotes induced microvesicle release from blood cells early in infection. Upon their release, microvesicles formed a complex on the T. cruzi surface with the complement C3 convertase, leading to its stabilization and inhibition, and ultimately resulting in increased parasite survival. Furthermore, we found that TGF-ß-bearing microvesicles released from monocytes and lymphocytes promoted rapid cell invasion by T. cruzi, which also contributed to parasites escaping the complement attack. In addition, in vivo infection with T. cruzi showed a rapid increase of microvesicle levels in mouse plasma, and infection with exogenous microvesicles resulted in increased T. cruzi parasitemia. Altogether, these data support a role for microvesicles contributing to T. cruzi evasion of innate immunity.
Assuntos
Membrana Celular/metabolismo , Doença de Chagas/imunologia , Convertases de Complemento C3-C5/metabolismo , Vesículas Citoplasmáticas/imunologia , Vesículas Citoplasmáticas/metabolismo , Evasão da Resposta Imune , Trypanosoma cruzi/imunologia , Animais , Células Cultivadas , Doença de Chagas/parasitologia , Doença de Chagas/patologia , Eritrócitos/ultraestrutura , Interações Hospedeiro-Patógeno , Humanos , Imunidade Inata , Linfócitos/imunologia , Camundongos , Camundongos Endogâmicos BALB C , Monócitos/imunologia , Fator de Crescimento Transformador beta/metabolismo , Trypanosoma cruzi/metabolismo , Trypanosoma cruzi/patogenicidadeRESUMO
Giardia intestinalis (syn. G. lamblia, G. duodenalis) is a flagellated unicellular eukaryotic microorganism that commonly causes diarrheal disease throughout the world. In humans, the clinical effects of Giardia infection range from the asymptomatic carrier state to a severe malabsorption syndrome possibly due to different virulence of the Giardia strain, the number of cysts ingested, the age of the host, and the state of the host immune system at the time of infection. The question about how G. intestinalis is controlled by the organism remains unanswered. Here, we investigated the role of the complement system and in particular, the lectin pathway during Giardia infections. We present the first evidence that G. intestinalis activate the complement lectin pathway and in doing so participate in eradication of the parasite. We detected rapid binding of mannan-binding lectin, H-ficolin and L-ficolin to the surface of G. intestinalis trophozoites and normal human serum depleted of these molecules failed to kill the parasites. Our finding provides insight into the role of lectin pathway in the control of G. intestinalis and about the nature of surface components of parasite.
Assuntos
Lectina de Ligação a Manose da Via do Complemento , Proteínas do Sistema Complemento/imunologia , Giardia lamblia/imunologia , Giardíase/imunologia , Interações Hospedeiro-Parasita/imunologia , Lectina de Ligação a Manose/imunologia , Giardíase/parasitologia , Humanos , Imunidade Inata , Lectinas/imunologia , FicolinasRESUMO
The complement system is the first line of defence against pathogen infection and can be activated by the classic, alternative and lectin pathways. Trypanosoma cruzi, the causative agent of Chagas disease, has to evade complement system killing and invade the host cells to progress in infection. T. cruzi infectious stages resist complement-mediated killing by expressing surface receptors, which dissociate or prevent C3 convertase formation. Here, we present the first evidence that T. cruzi activates the complement lectin pathway. We detected rapid binding of mannan-binding lectin, H-ficolin, and L-ficolin to the surface of T. cruzi, and found that serum depleted of these molecules failed to kill parasites. Furthermore, lectin pathway activation by T. cruzi required the MBL-associated serine protease 2 (MASP2) activity resulting in C2 factor cleavage. In addition, we demonstrate that the infectious stage of T. cruzi inhibits the lectin pathway activation and complement killing expressing the complement C2 receptor inhibitor trispanning (CRIT) protein. Transgenic parasites overexpressing CRIT were highly resistant to complement-mediated killing. CRIT-derived peptides inhibited both C2 binding to the surface of T. cruzi and parasite killing. Biochemical studies revealed that the CRIT extracellular domain 1 inhibits MASP2 cleavage of C2 factor and thereby impairs C3 convertase formation. Our findings establish that the complement lectin pathway recognizes T. cruzi and provide molecular insights into how the infectious stage inhibits this activation to resist complement system killing.
Assuntos
Lectina de Ligação a Manose da Via do Complemento/imunologia , Trypanosoma cruzi/citologia , Trypanosoma cruzi/imunologia , Animais , Morte Celular , Membrana Celular/metabolismo , Complemento C2/imunologia , Complemento C4/imunologia , Glicosilação , Humanos , Lectinas/sangue , Lectinas/metabolismo , Estágios do Ciclo de Vida , Lectina de Ligação a Manose/metabolismo , Serina Proteases Associadas a Proteína de Ligação a Manose/imunologia , Polissacarídeos/metabolismo , Ligação Proteica , Estrutura Terciária de Proteína , Receptores de Superfície Celular/química , Receptores de Superfície Celular/metabolismo , Proteínas Recombinantes/metabolismo , Soro , Trypanosoma cruzi/crescimento & desenvolvimento , FicolinasRESUMO
The ability to resist complement differs between the Y and Colombiana Trypanosoma cruzi strains. We found that the Y strain of T. cruzi was more able to resist the classical and lectin pathways of complement activation than the Colombiana strain. The complement C2 receptor inhibitor trispanning gene (CRIT) is highly conserved in both strains. At the protein level, CRIT is expressed only in stationary-phase epimastigotes of the Y but not the Colombiana strain and is expressed in infectious metacyclic trypomastigotes of both strains. Y strain epimastigotes with an overexpressed CRIT gene (pTEX-CRIT) had higher survival in normal human serum (NHS). Overexpression of the Y strain CRIT gene in Colombiana epimastigote forms increased the parasite's resistance to lysis mediated by the classical and lectin pathways but not to lysis mediated by alternative pathways. CRIT involvement on the parasite surface was confirmed by showing that the lytic activity of NHS against epimastigotes could be restored by adding excess C2.