The cell envelope of pathogenic mycobacteria interfaces with the host. As such, the interaction of bacterial products localized at or released from the cell surface with the host’s immune system can determine the fate of the bacterium in its host. In this study, the effects of three different types of Mycobacterium bovis cell envelope fractions—purified protein derivative, total cell wall lipids and culture supernatant and surface extract—on bovine dendritic cells were assessed. We found that the culture supernatant and surface extract fraction induced little to no production of the pro-inflammatory cytokines TNF-α and IL-12 in bovine dendritic cells. Moreover, this muted response was associated with poor activation of ERK and NF-κB, both of which are critical for the pro-inflammatory response. Furthermore, culture supernatant and surface extract treatment increased the expression of suppressor of cytokine signaling 1 and 3, both of which are negative regulators of pro-inflammatory signaling, in bovine dendritic cells. These observations taken together suggest the M. bovis culture supernatant and surface extract fraction contain immunomodulatory molecules that may aid in M. bovis pathogenesis.

致病性分枝杆菌的细胞包膜与宿主接触。因此，位于细胞表面或从细胞表面释放的细菌产物与宿主免疫系统的相互作用可以决定细菌在宿主中的命运。在本研究中，三种不同类型牛分枝杆菌的作用评估了牛树突细胞上的细胞包膜组分——纯化的蛋白质衍生物、总细胞壁脂质和培养物上清液和表面提取物。我们发现培养物上清液和表面提取物部分几乎不诱导牛树突细胞中促炎细胞因子 TNF-α 和 IL-12 的产生。此外，这种减弱的反应与 ERK 和 NF-κB 的激活不良有关，这两者对于促炎反应都至关重要。此外，培养上清液和表面提取物处理增加了牛树突细胞中细胞因子信号传导抑制因子 1 和 3 的表达，这两者都是促炎信号传导的负调节因子。这些观察结果综合起来表明M. bovis培养物上清液和表面提取物部分含有可能有助于牛分枝杆菌发病机制的免疫调节分子。