Brucella proline racemase protein A targets Tpl2 to promote IL-10 secretion for establishment of chronic infection

IL-10, an anti-inflammatory cytokine, plays a crucial role in limiting immune responses to pathogens, preventing host damage. However, the mechanisms underlying Brucella-mediated IL- 10 production remain incompletely understood. In this study, we demonstrate that the proline racemase protein A (PrpA) of Brucella melitensis M5-90 induces macrophages to secrete IL-10 by activating the Tpl2-ERK signaling pathway, thereby promoting chronic infection. Moreover, Tpl2 deletion impairs macrophage bactericidal ability, accompanied by reduced TNF- and IL-1{beta} but unaffected IL-10 levels. Additionally, Trp309, Glu103, and Glu129 of PrpA participate in interaction with Tpl2, but these residues do not influence PrpA-mediated IL-10 production in macrophages. PrpA deletion enhances IFN-{gamma} levels, specific anti-Brucella IgG, and CD4+ and CD8+ T cell numbers in mice. Furthermore, the Brucella melitensis M5-90 prpA mutant provides higher protection than the parental strain against virulent Brucella melitensis M28 infection in mice. Our findings suggest that Brucella PrpA promotes IL-10 secretion by macrophages through Tpl2 activation for bacterial survival and persistent infection, making the Brucella melitensis M5-90 prpA mutant a promising vaccine for enhanced protection. Author SummaryIL-10, an anti-inflammatory cytokine, is exploited by Brucella for survival. We identified Brucella PrpA as a potent IL-10 inducer, activating the Tpl2-ERK signaling pathway. Tpl2 deletion increased Brucella survival in macrophages, accompanied by reduced TNF- and IL-1{beta} but unaffected IL-10 secretion. Residues (Trp309, Glu103, and Glu129) of PrpA were crucial for interaction with Tpl2, yet did not impact PrpA-mediated IL-10 production. The B. melitensis M5-90 prpA mutant induced higher anti-Brucella IgG, IFN-{gamma}, and CD4+ and CD8+ T cell numbers in mice, providing better protection than B. melitensis M5-90. These findings unveil PrpAs role in IL-10 production and highlight the potential of the B. melitensis M5-90 prpA mutant as a promising vaccine for further evaluation.