A B lymphocyte mitogen is aBrucella abortusvirulence factor required for persistent infection

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Abstract
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 aBrucella abortusgene (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 aB. abortus-prpAmutant allowed us to assess the contribution of PrpA to the infection process. Mice infected withB. abortusinduced an early and transient nonresponsive status of splenocytes to bothEscherichia coliLPS and ConA. This phenomenon was not observed when mice were infected with aB. abortus-prpAmutant. Moreover, theB. abortus-prpAmutant 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 byBrucella.

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