Pasteurella leukotoxins are exotoxins that attack host leukocytes and especially polymorphonuclear cells, by causing cell rupture. The leukotoxin binds to the host LFA-1 integrin and induces a signaling cascade leading to many biological effects, including tyrosine phosphorylation of the CD18 tail, elevation of the intracellular Ca(2+) and lysis of the host cell. This leukotoxin is a major contributor to the pathogenesis of lung injury in ovine pneumonic pasteurellosis. It has also weak hemolytic activity