CD11b of Ovis canadensis and Ovis aries: Molecular cloning and characterization

Leukotoxin (Lkt) is the primary virulence factor secreted by Mannheimia haemolytica which causes pneumonia in ruminants. Previously, we have shown that CD18, the β subunit of β2 integrins, mediates Lkt-induced cytolysis of ruminant leukocytes. CD18 associates with four distinct α subunits giving rise to four β2 integrins, CD11a/CD18 (LFA-1), CD11b/CD18 (Mac-1), CD11c/CD18 (CR4), and CD11d/CD18. It is not known whether all the β2 integrins serve as a receptor for Lkt. Since PMNs are the leukocyte subset that is most susceptible to Lkt, and Mac-1 expression on PMNs exceeds that of other β2 integrins, it is of interest to determine whether Mac-1 serves as a receptor for Lkt which necessitates the cloning of CD11b and CD18. In this study, we cloned and sequenced the cDNA encoding CD11b of Ovis canadensis (bighorn sheep) and Ovis aries (domestic sheep). CD11b cDNA is 3455 nucleotides long encoding a polypeptide of 1152 amino acids. CD11b polypeptides from these two species exhibit 99% identity with each other, and 92% with that of cattle, and 70–80% with that of the non-ruminants analyzed.