Sequence of primers used for qPCR assays.

Leptospirosis is a global zoonotic threat caused by pathogenic Leptospira, and it remains challenging to combat because of persistent bottlenecks in vaccine development. The lack of well-defined protective antigens across Leptospira serovars continues to necessitate reliance on whole-cell inactivated vaccines, despite their recognized limitations: suboptimal efficacy and the absence of cross-serovar protection. In this study, we presented a Limosilactobacillus caviae (L. caviae) JL20 that significantly potentiated leptospiral vaccine efficacy through adjuvant-like effects. Survival assessment of hamsters demonstrated that JL20 enhances both vaccine efficacy and cross-protection. Oral JL20 significantly increased vaccine-induced cross-reactive binding antibody titers and total IgG antibody responses. In addition, JL20 exerted a priming effect in splenic macrophages, augmenting the expression of IL-1β and IL-6 in response to leptospiral vaccine stimulation, with a parallel enhancement in glycolytic activity. In vivo experiments demonstrated that JL20 significantly upregulated the expression of surface molecules CD38, CD69, and CD25 on T cells, as well as the production of the cytokine IL-2. JL20 enhanced the surface expression of key markers—including CD40, CD80, CD86, and MHC-II—on B cells. These effects indicate that JL20 enhances both cellular and humoral immune responses of leptospiral vaccine.钩端螺旋体病（Leptospirosis）是由致病性钩端螺旋体（Leptospira）引发的全球性人畜共患病威胁，由于疫苗研发始终存在瓶颈，其防控工作仍颇具挑战。目前，钩端螺旋体各血清型（serovars）间缺乏明确界定的保护性抗原，这使得学界仍不得不依赖全细胞灭活疫苗（whole-cell inactivated vaccines），尽管这类疫苗存在公认的局限性：效力欠佳且无法提供跨血清型保护。本研究报道了一株豚鼠乳酸杆菌（Limosilactobacillus caviae，L. caviae）JL20，其可通过佐剂样作用显著提升钩端螺旋体疫苗的保护效力。金黄地鼠存活实验结果显示，JL20可同时增强疫苗效力与跨血清型保护能力。口服JL20可显著提升疫苗诱导的交叉反应结合抗体滴度与总IgG抗体应答水平。此外，JL20可对脾脏巨噬细胞产生致敏作用，在钩端螺旋体疫苗刺激下，可上调白细胞介素1β（IL-1β）与白细胞介素6（IL-6）的表达，同时伴随糖酵解活性的增强。体内实验表明，JL20可显著上调T细胞表面分子CD38、CD69与CD25的表达水平，并促进细胞因子白细胞介素2（IL-2）的产生；同时可增强B细胞表面关键标志物——包括CD40、CD80、CD86与主要组织相容性复合体II（MHC-II）——的表面表达。上述效应表明，JL20可同时增强钩端螺旋体疫苗的细胞免疫与体液免疫应答。