RESUMEN
Brucellosis, a disease caused by the gram-negative bacterium Brucella spp., is a widespread zoonosis that inflicts important animal and human health problems, especially in developing countries. One of the hallmarks of Brucella infection is its capacity to establish a chronic infection, characteristic that depends on a wide repertoire of virulence factors among which are immunomodulatory proteins such as PrpA (encoding the proline racemase protein A or hydroxyproline-2-epimerase), involved in the establishment of the chronic phase of the infectious process that we have previously identified and characterized. We report here that, in vivo, Brucella abortus prpA is responsible for an increment in the B-cell number and in the specific antibody response and that these antibodies promote cell infection. We additionally found that Brucella alters the cytokine levels of IFN-γ, IL-10, TGFß1 and TNFα during the acute phase of the infectious process in a prpA dependent manner.
Asunto(s)
Isomerasas de Aminoácido/inmunología , Proteínas Bacterianas/inmunología , Brucella abortus/enzimología , Brucelosis/inmunología , Brucelosis/microbiología , Isomerasas de Aminoácido/genética , Animales , Anticuerpos Antibacterianos/inmunología , Linfocitos B/inmunología , Proteínas Bacterianas/genética , Brucella abortus/genética , Brucella abortus/inmunología , Brucelosis/genética , Femenino , Humanos , Interferón gamma/genética , Interferón gamma/inmunología , Interleucina-10/metabolismo , Ratones , Ratones Endogámicos BALB C , Factor de Necrosis Tumoral alfa/genética , Factor de Necrosis Tumoral alfa/inmunología , Factores de Virulencia/genética , Factores de Virulencia/inmunologíaRESUMEN
Brucella spp. and Trypanosoma cruzi are two intracellular pathogens that have no evolutionary common origins but share a similar lifestyle as they establish chronic infections for which they have to circumvent the host immune response. Both pathogens have a virulence factor (prpA in Brucella and tcPrac in T. cruzi) that induces B-cell proliferation and promotes the establishment of the chronic phase of the infectious process. We show here that, even though PrpA promotes B-cell proliferation, it targets macrophages in vitro and is translocated to the cytoplasm during the intracellular replication phase. We observed that PrpA-treated macrophages induce the secretion of a soluble factor responsible for B-cell proliferation and identified nonmuscular myosin IIA (NMM-IIA) as a receptor required for binding and function of this virulence factor. Finally, we show that the Trypanosoma cruzi homologue of PrpA also targets macrophages to induce B-cell proliferation through the same receptor, indicating that this virulence strategy is conserved between a bacterial and a protozoan pathogen.
Asunto(s)
Linfocitos B/inmunología , Proteínas Bacterianas/inmunología , Proliferación Celular , Macrófagos/inmunología , Factores de Virulencia/inmunología , Isomerasas de Aminoácido/genética , Isomerasas de Aminoácido/inmunología , Isomerasas de Aminoácido/metabolismo , Animales , Linfocitos B/citología , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Western Blotting , Brucella abortus/inmunología , Brucella abortus/metabolismo , Brucella abortus/patogenicidad , Línea Celular , Células Cultivadas , Femenino , Macrófagos/parasitología , Macrófagos/virología , Ratones , Ratones Endogámicos BALB C , Microscopía Fluorescente , Miosina Tipo IIA no Muscular/inmunología , Miosina Tipo IIA no Muscular/metabolismo , Unión Proteica , Proteínas Protozoarias/genética , Proteínas Protozoarias/inmunología , Proteínas Protozoarias/metabolismo , Bazo/citología , Bazo/inmunología , Bazo/metabolismo , Trypanosoma cruzi/inmunología , Trypanosoma cruzi/metabolismo , Trypanosoma cruzi/patogenicidad , Virulencia/inmunología , Factores de Virulencia/genética , Factores de Virulencia/metabolismoRESUMEN
Microbial pathogens with the ability to establish chronic infections have evolved strategies to actively modulate the host immune response. Brucellosis is a disease caused by a Gram-negative intracellular pathogen that if not treated during the initial phase of the infection becomes chronic as the bacteria persist for the lifespan of the host. How this pathogen and others achieve this action is a largely unanswered question. We report here the identification of a Brucella abortus gene (prpA) directly involved in the immune modulation of the host. PrpA belongs to the proline-racemase family and elicits a B lymphocyte polyclonal activation that depends on the integrity of its proline-racemase catalytic site. Stimulation of splenocytes with PrpA also results in IL-10 secretion. Construction of a B. abortus-prpA mutant allowed us to assess the contribution of PrpA to the infection process. Mice infected with B. abortus induced an early and transient nonresponsive status of splenocytes to both Escherichia coli LPS and ConA. This phenomenon was not observed when mice were infected with a B. abortus-prpA mutant. Moreover, the B. abortus-prpA mutant had a reduced capacity to establish a chronic infection in mice. We propose that an early and transient nonresponsive immune condition of the host mediated by this B cell polyclonal activator is required for establishing a successful chronic infection by Brucella.