The virulence of both Actinobacillus actinomycetemcomitans (stomatitis in humans) and Mannheimia haemolytica (pneumonia in cattle) is clearly associated with the ligand-receptor interactions between their respective leukotoxin and CD11a/CD18, which triggers the synthesis and release of a wide array of cytokines and chemoattractants that exacerbate inflammation, and ultimately results in massive leukolysis [13,14]. This evidence concerns the gene ITGB2 and pneumonia.