Tarigan S, Slocombe R F, Browning G F, Kimpton W
School of Veterinary Science, University of Melbourne, Parkville, Australia.
Am J Vet Res. 1994 Nov;55(11):1548-57.
Alterations in the size and functions of porcine alveolar macrophages exposed to sublytic amounts of heat-labile, hemolytic cytotoxin produced by Actinobacillus pleuropneumoniae (App) serotype 1, strain HS54 into the culture medium were studied in vitro. Alveolar macrophages were sensitive to the cytotoxin; treatment of the macrophages with low concentrations of cytotoxin (0.016 hemolytic unit) resulted in severe, irreversible cell swelling. However, high doses of cytotoxin (2.0 hemolytic units) were required to cause substantial cell death, as indicated by the influx of propidium iodide into and release of lactate dehydrogenase from cells. Macrophages exposed to low, sublytic doses of cytotoxin failed to migrate toward chemoattractant, were unable to attach to glass, and failed to phagocytize optimally opsonized erythrocytes. Macrophages already attached to glass surfaces detached when exposed to sublytic doses of cytotoxin. The swelling and impairment of functions of alveolar macrophages observed in this study could not be attributed to endotoxic effects, because heat treatment of the cytotoxin preparation for 60 minutes at 60 C resulted in complete loss of cytotoxicity. We conclude that sublytic doses of heat-labile, hemolytic cytotoxic substances produced by App depress alveolar macrophage function at concentrations likely to develop in association with acute pulmonary infection with App. The Apx (A pleuropneumoniae Rtx toxins) exotoxins secreted by the bacteria into culture medium were considered responsible for the toxic activity of the cytotoxin preparation. The Apx of the App field strain used in this study were likely to be similar to those of serotype-1 reference strain (S4707). Analysis by use of DNA-DNA hybridization indicated that genomic DNA of the field strain contained sequences similar to those encoding structural protein of ApxI (apxIA) and ApxII (apxIIA) of the serotype-1 reference strain. Therefore, Apx produced by the field strain of App used in this study are likely to be of similar pathogenic importance worldwide.
体外研究了猪肺泡巨噬细胞暴露于胸膜肺炎放线杆菌（App）血清型1菌株HS54产生的亚溶细胞剂量的热不稳定溶血细胞毒素后，其大小和功能的变化。肺泡巨噬细胞对该细胞毒素敏感；用低浓度细胞毒素（0.016溶血单位）处理巨噬细胞会导致严重的、不可逆的细胞肿胀。然而，高剂量细胞毒素（2.0溶血单位）才会导致大量细胞死亡，这可通过碘化丙啶流入细胞以及细胞内乳酸脱氢酶释放来表明。暴露于低剂量亚溶细胞毒素的巨噬细胞无法向趋化因子迁移，无法附着于玻璃，也无法最佳地吞噬调理过的红细胞。已经附着于玻璃表面的巨噬细胞在暴露于亚溶细胞毒素剂量时会脱离。本研究中观察到的肺泡巨噬细胞肿胀和功能受损不能归因于内毒素作用，因为将细胞毒素制剂在60℃热处理60分钟会导致细胞毒性完全丧失。我们得出结论，App产生的亚溶细胞剂量的热不稳定溶血细胞毒性物质在与App急性肺部感染相关的可能浓度下会抑制肺泡巨噬细胞功能。细菌分泌到培养基中的Apx（胸膜肺炎放线杆菌RTX毒素）外毒素被认为是细胞毒素制剂毒性活性的原因。本研究中使用的App田间菌株的Apx可能与血清型1参考菌株（S4707）的Apx相似。通过DNA - DNA杂交分析表明，田间菌株的基因组DNA包含与血清型1参考菌株的ApxI（apxIA）和ApxII（apxIIA）结构蛋白编码序列相似的序列。因此，本研究中使用的App田间菌株产生的Apx在全球范围内可能具有相似的致病重要性。
