Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology of the CAS, Prague, Czech Republic
Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology of the CAS, Prague, Czech Republic.
mBio. 2019 Sep 24;10(5):e01743-19. doi: 10.1128/mBio.01743-19.
Monocytes arriving at the site of infection differentiate into functional effector macrophages to replenish the resident sentinel cells. , the pertussis agent, secretes an adenylate cyclase toxin-hemolysin (CyaA) that binds myeloid phagocytes through complement receptor 3 (CD11b/CD18) and swiftly delivers its adenylyl cyclase enzyme domain into phagocytes. This ablates the bactericidal capacities of phagocytes through massive and unregulated conversion of cytosolic ATP into the key signaling molecule cAMP. We show that exposure of primary human monocytes to as low a concentration as 22.5 pM CyaA, or a low (2:1) multiplicity of infection by CyaA-producing bacteria, blocks macrophage colony-stimulating factor (M-CSF)-driven differentiation of monocytes. CyaA-induced cAMP signaling mediated through the activity of protein kinase A (PKA) efficiently blocked expression of macrophage markers, and the monocytes exposed to 22.5 pM CyaA failed to acquire the characteristic intracellular complexity of mature macrophage cells. Neither M-CSF-induced endoplasmic reticulum (ER) expansion nor accumulation of Golgi bodies, mitochondria, or lysosomes was observed in toxin-exposed monocytes, which remained small and poorly phagocytic and lacked pseudopodia. Exposure to 22.5 pM CyaA toxin provoked loss of macrophage marker expression on differentiated macrophages, as well as on primary human alveolar macrophages, which appeared to dedifferentiate into monocyte-like cells with upregulated CD14 levels. This is the first report that terminally differentiated tissue-resident macrophage cells can be dedifferentiated The results suggest that blocking of monocyte-to-macrophage transition and/or dedifferentiation of the sentinel cells of innate immunity through cAMP-elevating toxin action may represent a novel immune evasion strategy of bacterial pathogens. Macrophages are key sentinel cells of the immune system, and, as such, they are targeted by the toxins produced by the pertussis agent The adenylate cyclase toxin (CyaA) mediates immune evasion of by suspending the bactericidal activities of myeloid phagocytes. We reveal a novel mechanism of potential subversion of host immunity, where CyaA at very low (22 pM) concentrations could inhibit maturation of human monocyte precursors into the more phagocytic macrophage cells. Furthermore, exposure to low CyaA amounts has been shown to trigger dedifferentiation of mature primary human alveolar macrophages back into monocyte-like cells. This unprecedented capacity is likely to promote survival of the pathogen in the airways, both by preventing maturation of monocytes attracted to the site of infection into phagocytic macrophages and by dedifferentiation of the already airway-resident sentinel cells.
单核细胞到达感染部位后分化为具有功能的效应巨噬细胞，以补充常驻的哨兵细胞。百日咳菌产生一种腺苷酸环化酶毒素-溶血素（CyaA），通过补体受体 3（CD11b/CD18）与髓样吞噬细胞结合，并迅速将其腺苷酸环化酶酶结构域递送至吞噬细胞内。这通过大量且不受调节的将胞质溶胶中的 ATP 转化为关键信号分子 cAMP，从而消除吞噬细胞的杀菌能力。我们表明，人类单核细胞暴露于低至 22.5 pM CyaA 的浓度，或暴露于产生 CyaA 的细菌的低（2:1）感染复数，可阻断巨噬细胞集落刺激因子（M-CSF）驱动单核细胞的分化。CyaA 诱导的 cAMP 信号通过蛋白激酶 A（PKA）的活性介导，有效地阻断了巨噬细胞标志物的表达，并且暴露于 22.5 pM CyaA 的单核细胞未能获得成熟巨噬细胞细胞的特征性细胞内复杂性。在毒素暴露的单核细胞中均未观察到内质网（ER）扩张或高尔基体、线粒体或溶酶体的积累，这些单核细胞仍然较小且吞噬能力差，并且缺乏伪足。22.5 pM CyaA 毒素的暴露会导致分化的巨噬细胞以及原代人肺泡巨噬细胞上的巨噬细胞标志物表达丧失，这些细胞似乎分化为 CD14 水平上调的单核样细胞。这是第一个报道终末分化的组织驻留巨噬细胞可以去分化的研究。结果表明，通过 cAMP 升高毒素作用阻断单核细胞向巨噬细胞的转化和/或固有免疫哨兵细胞的去分化，可能代表细菌病原体的一种新的免疫逃避策略。巨噬细胞是免疫系统的关键哨兵细胞，因此它们是百日咳菌产生的毒素的靶向细胞。腺苷酸环化酶毒素（CyaA）通过抑制髓样吞噬细胞的杀菌活性来介导对 的免疫逃避。我们揭示了一种潜在宿主免疫颠覆的新机制，其中非常低浓度的 CyaA（22 pM）可抑制人类单核细胞前体成熟为更具吞噬能力的巨噬细胞。此外，已经表明暴露于低浓度的 CyaA 会触发成熟的原代人肺泡巨噬细胞分化回单核样细胞。这种前所未有的能力可能通过阻止被吸引到感染部位的单核细胞成熟为吞噬细胞，以及通过分化已经驻留在气道中的哨兵细胞，来促进病原体在气道中的存活。
