Hoover D L, Friedlander A M, Rogers L C, Yoon I K, Warren R L, Cross A S
Department of Bacterial Diseases, Walter Reed Army Institute of Research, Washington, D.C. 20307.
Infect Immun. 1994 Oct;62(10):4432-9. doi: 10.1128/iai.62.10.4432-4439.1994.
Bacillus anthracis exotoxins mediate most of the symptomatology of severe anthrax. In addition to a clinical syndrome reminiscent of septic shock, which may be mediated by cytokines produced by macrophages stimulated with lethal toxin, infected patients show profound edema at sites of infection. Edema is mediated by edema toxin (ET), which comprises of a binding molecule, protective antigen, and an active moiety, edema factor, which possesses intrinsic adenylyl cyclase activity. Intracellular cyclic AMP (cAMP) regulates the production of several cytokines that modulate edema formation and play important roles in host defense against invading bacteria. To determine whether ET enhanced the accumulation of cAMP in monocytes and thereby influenced cytokine production, we cultured human monocytes with endotoxin (lipopolysaccharide [LPS]) and dilutions of ET and determined the levels of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) in culture supernatant fluids. We further estimated cytokine-specific mRNA accumulation in monocytes by reverse transcription PCR and examined intracellular cAMP concentrations following treatment with ET. ET and LPS each induced monocytes to secrete comparable amounts of IL-6. ET did not inhibit and in most experiments modestly enhanced LPS-induced IL-6 production. In contrast to this stimulatory effect on IL-6 production, ET induced little or no TNF-alpha production. Moreover, ET profoundly inhibited LPS-induced TNF-alpha synthesis. These regulatory phenomena were also observed at the mRNA level in association with dose-related enhancement of intracellular cAMP in ET-treated monocytes. Monocytes treated with dibutyryl cAMP, an active analog of cAMP, produced cytokines in a pattern identical to that of cells treated with ET. The disruption of cytokine networks as a consequence of unregulated, ET-induced cAMP accumulation in human monocytes may impair cellular antimicrobial responses and contribute to clinical signs and symptoms.
炭疽芽孢杆菌外毒素介导了严重炭疽的大部分症状表现。除了类似于脓毒症休克的临床综合征（可能由致死毒素刺激巨噬细胞产生的细胞因子介导）外，受感染患者在感染部位还会出现严重水肿。水肿由水肿毒素（ET）介导，ET由一个结合分子保护性抗原和一个活性部分水肿因子组成，水肿因子具有内在的腺苷酸环化酶活性。细胞内的环磷酸腺苷（cAMP）调节几种细胞因子的产生，这些细胞因子可调节水肿形成，并在宿主抵御入侵细菌的过程中发挥重要作用。为了确定ET是否会增加单核细胞中cAMP的积累，从而影响细胞因子的产生，我们用内毒素（脂多糖[LPS]）和不同稀释度的ET培养人单核细胞，并测定培养上清液中白细胞介素-6（IL-6）和肿瘤坏死因子α（TNF-α）的水平。我们还通过逆转录PCR进一步估计单核细胞中细胞因子特异性mRNA的积累，并检测ET处理后细胞内cAMP的浓度。ET和LPS各自诱导单核细胞分泌相当数量的IL-6。ET没有抑制作用，并且在大多数实验中适度增强了LPS诱导的IL-6产生。与对IL-6产生的这种刺激作用相反，ET几乎不诱导或不诱导TNF-α产生。此外，ET显著抑制LPS诱导的TNF-α合成。在mRNA水平上也观察到了这些调节现象，同时ET处理的单核细胞中细胞内cAMP呈剂量相关的增加。用cAMP的活性类似物二丁酰cAMP处理的单核细胞产生细胞因子的模式与用ET处理的细胞相同。由于ET诱导的cAMP在人单核细胞中不受调节地积累而导致的细胞因子网络破坏，可能会损害细胞的抗菌反应，并导致临床症状和体征。
