Lawrence Paulraj K, Dassanayake Rohana P
Department of Veterinary Microbiology and Pathology, Washington State University, Dairy Road, Pullman, WA 99164-7040, USA.
Vet Immunol Immunopathol. 2010 Jun 15;135(3-4):266-74. doi: 10.1016/j.vetimm.2009.12.007. Epub 2009 Dec 29.
Pneumonia caused by Mannheimia haemolytica is an important disease of domestic sheep (DS, Ovis aries) and cattle (BO). M. haemolytica is a normal commensal of the upper respiratory tract in ruminants, but during stress and viral infection it breaches the host innate mucosal defense and descents into lungs causing fibrinous pleuropneumonia. Leukotoxin (Lkt) produced by M. haemolytica is cytolytic to all subsets of ruminant leukocytes. Earlier, we and others have shown that DS and BO LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) can mediate Lkt-induced cytolysis. It is not clear whether CR4 (CD11c/CD18), which is involved in chemotaxis, phagocytosis and regulates host immune response can also mediate Lkt-induced cytolysis in ruminants. The host innate immune response to M. haemolytica is poorly understood and the involvement of CR4 in M. haemolytica pathogenesis is one of the most understudied. This problem is further compounded by the lack of cd11c genes from any ruminant species. Therefore, the objectives of this study were to clone cd11c and determine whether CR4 can serve as a receptor for Lkt. In this direction we cloned two alleles of cd11c gene from leukocytes isolated from DS blood by RT-PCR. Transfectants developed expressing functional DS CR4 were found to be cytotoxic to Lkt from four different isolates of M. haemolytica. This is the first report confirming the ability of a recombinant ovine CR4 to bind to M. haemolytica Lkt and mediate concentration-dependent lysis of host cells, thus, confirming their role in M. haemolytica pathogenesis. This is a critical step in understanding host innate immunity and the management of pneumonia in sheep.
溶血曼氏杆菌引起的肺炎是家养绵羊（DS，绵羊属）和牛（BO）的一种重要疾病。溶血曼氏杆菌是反刍动物上呼吸道的正常共生菌，但在应激和病毒感染期间，它会突破宿主先天性黏膜防御，进入肺部，引发纤维素性胸膜肺炎。溶血曼氏杆菌产生的白细胞毒素（Lkt）对反刍动物白细胞的所有亚群都具有细胞溶解作用。此前，我们和其他人已经表明，DS和BO的淋巴细胞功能相关抗原-1（LFA-1，CD11a/CD18）和巨噬细胞-1抗原（Mac-1，CD11b/CD18）可介导Lkt诱导的细胞溶解。尚不清楚参与趋化作用、吞噬作用并调节宿主免疫反应的补体受体4（CR4，CD11c/CD18）是否也能介导反刍动物中Lkt诱导的细胞溶解。对溶血曼氏杆菌的宿主先天性免疫反应了解甚少，CR4在溶血曼氏杆菌发病机制中的作用是研究最少的领域之一。由于缺乏任何反刍动物物种的cd11c基因，这个问题更加复杂。因此，本研究的目的是克隆cd11c，并确定CR4是否可以作为Lkt的受体。在这个方向上，我们通过逆转录聚合酶链反应（RT-PCR）从DS血液中分离的白细胞中克隆了cd11c基因的两个等位基因。发现表达功能性DS CR4的转染体对来自四种不同溶血曼氏杆菌分离株的Lkt具有细胞毒性。这是第一份证实重组绵羊CR4能够结合溶血曼氏杆菌Lkt并介导宿主细胞浓度依赖性裂解的报告，从而证实了它们在溶血曼氏杆菌发病机制中的作用。这是理解宿主先天性免疫和绵羊肺炎管理的关键一步。
