Inflammation in the respiratory tract is thought to worsen the disease response to Mycoplasma bovis infection. This study investigated the cells involved in this response with a focus on proteases and cytokines as harmful effector mechanisms. By immunohistochemistry, Mac387-positive macrophages were the main cell type comprising the foci of caseous necrosis in cattle with M. bovis pneumonia. Thus, the study evaluated how priming of different types of macrophages with bacterial lysate (or pro-inflammatory cytokines induced by the bacterial lysate) affected their responses to M. bovis infection. Inducible responses were detected in monocyte-derived macrophages (M1-MDMs and M2-MDMs), whereas pulmonary alveolar macrophages (PAMs) were minimally affected by priming or infection. M. bovis-infected MDMs secreted MMP-12 and SPLA2, and priming with pro-inflammatory cytokines increased the secretion of cathepsin B in response to M. bovis infection. Of these, there were higher concentrations of cathepsin B and SPLA2 in lungs with M. bovis pneumonia compared to healthy lungs, and these are potential mechanisms for macrophage-induced lung damage in M. bovis infection. Priming of MDMs with either bacterial lysate or with pro-inflammatory cytokines caused an enhanced response to M. bovis infection with respect to IL-8 and IL-1β secretion. The findings of this study suggest proteases, lipases and cytokines derived from monocyte-derived macrophages as possible mediators by which prior inflammation in the respiratory tract worsen disease outcomes from M. bovis infection.

呼吸道炎症被认为会加重对牛支原体感染的疾病反应。这项研究调查了参与这种反应的细胞，重点是蛋白酶和细胞因子作为有害的效应机制。通过免疫组织化学，Mac387 阳性巨噬细胞是主要的细胞类型，包括牛分枝杆菌肺炎的干酪坏死灶。因此，该研究评估了用细菌裂解物（或由细菌裂解物诱导的促炎细胞因子）引发不同类型巨噬细胞如何影响它们对牛分枝杆菌的反应感染。在单核细胞衍生的巨噬细胞（M1-MDM 和 M2-MDM）中检测到诱导反应，而肺泡巨噬细胞 (PAM) 受启动或感染的影响最小。牛分枝杆菌感染的 MDM 会分泌 MMP-12 和 SPLA2，并且用促炎细胞因子启动会增加组织蛋白酶 B 的分泌，以响应牛分枝杆菌感染。其中，与健康肺相比，患有牛分枝杆菌肺炎的肺中组织蛋白酶 B 和 sPLA2 浓度更高，这些是巨噬细胞诱导的牛分枝杆菌感染肺损伤的潜在机制。用细菌裂解物或促炎细胞因子引发 MDM 导致对牛分枝杆菌的反应增强IL-8 和 IL-1β 分泌方面的感染。这项研究的结果表明，源自单核细胞衍生的巨噬细胞的蛋白酶、脂肪酶和细胞因子可能是之前呼吸道炎症的介质，从而使牛分枝杆菌感染的疾病结果恶化。