Abstract：
Brucella is an intracellular parasitic bacterium lacking typical virulence factors, and its pathogenicity primarily relies on replication within host cells. In this study, we observed a significant increase in spleen weight in mice immunized with a Brucella strain deleted of the gene for alanine racemase (Alr), the enzyme responsible for alanine racemization (Δalr). However, the bacterial load in the spleen markedly decreased in the mutant strain. Concurrently, the ratio of white pulp to red pulp in the spleen was increased, serum IgG levels were elevated, but no significant damage to other organs was observed. In addition, the inflammatory response was potentiated and the NF-κB-NLRP3 signaling pathway was activated in macrophages (RAW264.7 Cells and Bone Marrow-Derived Cells) infect ed with the Δalr mutant. Further investigation revealed that the Δalr mutant released substantial amounts of protein in a simulated intracellular environment which resulted in heightened inflammation and activation of the TLR4-NF-κB-NLRP3 pathway in macrophages. The consequent cytoplasmic exocytosis reduced intracellular Brucella survival. In summary, cytoplasmic exocytosis products resulting from infection with a Brucella strain deleted of the alr gene effectively activated the TLR4-NFκB-NLRP3 pathway, triggered a robust inflammatory response, and reduced bacterial survival within host cells. Moreover, the Δalr strain exhibits lower toxicity and stronger immunogenicity in mice.
摘要：
布鲁氏菌是一种缺乏典型毒力因子的胞内寄生菌,其致病性主要依赖于宿主细胞内的复制。在这项研究中,我们观察到用缺失丙氨酸消旋酶（Alr）基因的布鲁氏菌菌株免疫的小鼠脾脏重量显着增加，负责丙氨酸外消旋化的酶(Δalr)。然而,在突变菌株中，脾脏中的细菌负荷显着降低。同时,脾脏中白髓与红髓的比例增加，血清IgG水平升高，但未观察到对其他器官的明显损害。此外,在感染Δalr突变体的巨噬细胞（RAW264.7细胞和骨髓衍生细胞）中，炎症反应得到加强，NF-κB-NLRP3信号通路被激活。进一步的研究表明，Δalr突变体在模拟的细胞内环境中释放了大量的蛋白质，从而导致巨噬细胞中TLR4-NF-κB-NLRP3途径的炎症和激活。随后的细胞质胞吐减少了细胞内布鲁氏菌的存活。总之,由缺失alr基因的布鲁氏菌菌株感染导致的细胞质胞吐产物有效激活了TLR4-NFκB-NLRP3途径，引发了强烈的炎症反应，和减少宿主细胞内的细菌存活。此外，Δalr菌株在小鼠中表现出较低的毒性和较强的免疫原性。
