Participação dos receptores TLR2, TLR4, TLR9 e da molécula adaptadora MYD88 na infecção por Brucella ovis em camundongos C57/BL6 e a proteína TcpB como fator de virulência para Brucella ovis

Abstract

Brucella ovisis a significant cause of epididymitis and thus causes economic loss to the sheep industry by affecting animal reproduction. Considering the scarcity of studies on the interaction of B. ovis with innate system components, such as Toll-like receptors (TLR), this work highlights the importance of TLR signalling to resistance to B. ovis and the protein TcpB, described as an evasion mechanism of TLR signaling in B. abortus and B. melitensis, as a virulence factor. C57/BL6 knockout forTLR2, TLR4, TLR9, and MyD88 mice were infected with B. ovisand euthanized after seven days of infection (dpi) for bacteriologic, histopathologic and gene expression evaluation. MyD88-/- mice showed higher spleen colonization when compared with wild-type C57/BL6 mice. This increase in susceptibility was due to smaller inflammatory response in these animals, demonstrated by smaller inflammation in spleen and liver and smaller transcription of proinflammatory citokines such as TNF-and IL-6, necessary for proper response against Brucella. TLR9-/- mice also presented larger spleen bacterial colonization in comparison with wild-type mice, having, however, developed larger inflammatory response than the control group. TLR2-/- e TLR4-/- mice showed no diferent susceptibility to B. ovisinfection in comparison with wild-type mice. Therefore, MyD88 is necessary for the developmentof efficient inflammatory response against B. ovis in the murine model. Additionally, a mutant strain of B. ovis was generated from the deletion of the tcpBgene. B. ovis tcpB was inoculated in C57/BL6 mice and the infection kinetic was carried out. The absence of this gene resulted in in vivo attenuated phenotype, characterized by smaller bacterial colonization from 1 dpi and lack of capacity to persist in host. However, this mutant strain showed a growth defect in vitro. Therefore, the functional protein TcpB is necessary for B. ovisvirulence and survival in mice, but further bacteriological studies of the mutation developed in this work should be carried out to determineif the sample shows a metabolic or growth defect.