Differential Susceptibility of Bighorn Sheep (Ovis canadensis) and Domestic Sheep (Ovis aries) Neutrophils to Mannheimia haemolytica Leukotoxin is not due to Differential Expression of Cell Surface CD18.
Bighornsheep ( Ovis canadensis ) are more susceptible to pneumonia caused by Mannheimia haemolytica than are domestic sheep ( Ovis aries ). Leukotoxin produced by M. haemolytica is the principal virulence factor involved in pneumonia pathogenesis. Although leukotoxin is cytolytic to all subsets of ruminant leukocytes, neutrophils are the most susceptible subset. Bighorn sheep neutrophils are four- to eightfold more susceptible to leukotoxin-induced cytolysis than are domestic sheep neutrophils. We hypothesized that the higher susceptibility of bighorn sheep neutrophils, in comparison to domestic sheep neutrophils, is due to higher expression of CD18, the receptor for leukotoxin on leukocytes. Our objective was to quantify CD18 expression on neutrophils of bighorn sheep and domestic sheep. Cell-surface CD18 expression on bighorn sheep and domestic sheep neutrophils was measured as antibody binding capacity of cells by flow cytometric analysis with two fluorochrome-conjugated anti-CD18 monoclonal antibodies (BAQ30A and HUH82A) and microspheres. Contrary to our expectations, CD18 expression was higher (P<0.0001) with monoclonal antibody BAQ30A and was higher (P<0.0002) as well with monoclonal antibody HUH80A on domestic sheep neutrophils in comparison to bighorn sheep neutrophils. These findings suggest that the higher in vitro susceptibility to leukotoxin of bighorn sheep neutrophils compared to domestic sheep neutrophils is not due to higher expression of the leukotoxin receptor CD18 on bighorn sheep neutrophils.
1 Department of Veterinary Microbiology and Pathology, Washington State University, PO Box 647040, Pullman, Washington 99164, USA.|2 US Department of Agriculture, Agricultural Research Service, National Animal Disease Center, 1920 Dayton Ave., Ames, Iowa 50010, USA.
Rohana P
RP
Dassanayake
1 Department of Veterinary Microbiology and Pathology, Washington State University, PO Box 647040, Pullman, Washington 99164, USA.
Sudarvili
S
Shanthalingam
1 Department of Veterinary Microbiology and Pathology, Washington State University, PO Box 647040, Pullman, Washington 99164, USA.
Weiguo
W
Liu
2 US Department of Agriculture, Agricultural Research Service, National Animal Disease Center, 1920 Dayton Ave., Ames, Iowa 50010, USA.
Eduardo
E
Casas
1 Department of Veterinary Microbiology and Pathology, Washington State University, PO Box 647040, Pullman, Washington 99164, USA.
Subramaniam
S
Srikumaran
D000818:Animals; D005098:Exotoxins; D016978:Mannheimia haemolytica / Q000472:pathogenicity*; D009504:Neutrophils / Q000821:virology*; D012756:Sheep; D012757:Sheep Diseases / Q000821:virology; D034581:Sheep, Bighorn / Q000821:virology*; D034561:Sheep, Domestic
D005098:Exotoxins; C018579:leukotoxin
Bighorn sheep; CD18; Mannheimia haemolytica; Ovis canadensis; domestic sheep; flow cytometry; leukotoxin; pneumonia