Related Experiment Video
Updated: Jun 17, 2026
A Novel High-Throughput Ex Vivo Ovine Skin Wound Model for Testing Emerging Antibiotics
Published on: September 16, 2022
Ovis aries CR4 is involved in Mannheimia haemolytica leukotoxin-induced cytotoxicity
Paulraj K Lawrence1, Rohana P Dassanayake
1Department of Veterinary Microbiology and Pathology, Washington State University, Dairy Road, Pullman, WA 99164-7040, USA. pklawrence@vetmed.wsu.edu
Abstract:
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.
Insights
Researchers identified that ovine CR4 (CD11c/CD18) mediates Mannheimia haemolytica leukotoxin-induced cell lysis. This finding is crucial for understanding ovine pneumonia and host innate immunity.
Area of Science:
- Veterinary Immunology
- Ruminant Infectious Diseases
Background:
- Mannheimia haemolytica causes pneumonia in sheep and cattle.
- Leukotoxin (Lkt) from M. haemolytica lyses ruminant leukocytes.
- Previous studies identified LFA-1 and Mac-1 as receptors for Lkt, but CR4's role was unclear.
Purpose of the Study:
- To clone the ovine cd11c gene.
- To determine if CR4 can act as a receptor for M. haemolytica leukotoxin.
- To investigate CR4's role in M. haemolytica pathogenesis.
Main Methods:
- Cloned two alleles of the cd11c gene from domestic sheep leukocytes using RT-PCR.
- Developed transfectants expressing functional ovine CR4.
- Assessed the cytotoxicity of M. haemolytica leukotoxin on these transfectants.
Main Results:
- Successfully cloned ovine cd11c alleles.
- Ovine CR4 expressing transfectants showed susceptibility to Lkt-induced lysis from four M. haemolytica isolates.
- Demonstrated that recombinant ovine CR4 binds to M. haemolytica Lkt and mediates concentration-dependent cell lysis.
Conclusions:
- Ovine CR4 is confirmed as a functional receptor for M. haemolytica leukotoxin.
- CR4 plays a significant role in M. haemolytica pathogenesis by mediating host cell lysis.
- This research provides critical insights into ruminant innate immunity and sheep pneumonia management.
