Vanden Bergh Philippe G A C, Zecchinon Laurent L M, Fett Thomas, Desmecht Daniel
Department of Pathology, Faculty of Veterinary Medicine, University of Liege, Liège, Belgium.
Vet Res. 2009 Jul-Aug;40(4):33. doi: 10.1051/vetres/2009016. Epub 2009 Apr 10.
Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, produces Apx toxins that are recognized as major virulence factors. Recently, we showed that ApxIIIA-cytotoxic activity specifically targets Sus scrofa leukocytes. Since both LtxA from Aggregatibacter actinomycetem comitans (aggressive periodontitis in humans) and LktA from Mannheimia haemolytica (pneumonia in ruminants) share this characteristic, respectively towards human and ruminant leukocytes, and because both use the CD18 subunit to interact with their respective LFA-1, we hypothesized that ApxIIIA was likely to bind porcine CD18 to exercise its deleterious effects on pig leukocytes. A beta(2)-integrin-deficient ApxIIIA-resistant human erythroleukemic cell line was transfected either with homologous or heterologous CD11a/ CD18 heterodimers using a set of plasmids coding for human (ApxIIIA-resistant), bovine (-resistant) and porcine (-susceptible) CD11a and CD18 subunits. Cell preparations that switched from ApxIIIA-resistance to -susceptibility were then sought to identify the LFA-1 subunit involved. The results showed that the ApxIIIA-resistant recipient cell line was rendered susceptible only if the CD18 partner within the LFA-1 heterodimer was that of the pig. It is concluded that porcine CD18 is necessary to mediate A. pleuropneumoniae ApxIIIA toxin-induced leukolysis.
胸膜肺炎放线杆菌是猪胸膜肺炎的病原体，可产生被认为是主要毒力因子的Apx毒素。最近，我们发现ApxIIIA的细胞毒性活性特异性靶向猪白细胞。由于伴放线聚集杆菌（人类侵袭性牙周炎）的LtxA和溶血曼氏杆菌（反刍动物肺炎）的LktA分别对人类和反刍动物白细胞具有此特性，并且由于两者都利用CD18亚基与各自的LFA-1相互作用，我们推测ApxIIIA可能与猪CD18结合，从而对猪白细胞发挥其有害作用。使用一组编码人（对ApxIIIA耐药）、牛（耐药）和猪（敏感）CD11a和CD18亚基的质粒，将β(2)-整合素缺陷的对ApxIIIA耐药的人红白血病细胞系用同源或异源CD11a/CD18异二聚体进行转染。然后寻找从对ApxIIIA耐药转变为敏感的细胞制剂，以确定所涉及的LFA-1亚基。结果表明，只有当LFA-1异二聚体内的CD18伙伴是猪的CD18时，对ApxIIIA耐药的受体细胞系才会变得敏感。结论是猪CD18是介导胸膜肺炎放线杆菌ApxIIIA毒素诱导白细胞溶解所必需的。
