PASTEURELLA-HAEMOLYTICA LEUKOTOXIN INDUCES HISTAMINE-RELEASE FROM BOVINE PULMONARY MAST-CELLS

Pasteurella haemolytica A1 leukotoxic culture supernatant was evaluate d for its ability to induce histamine release from bovine pulmonary ma st cells isolated by enzymatic dispersion of lung tissue. Histamine wa s measured by a radioimmunoassay technique. Leukotoxic culture superna tant of P. haemolytica significantly released histamine in a time and concentration-related manner. This effect was lost when culture supern atant was heat-inactivated or preincubated with leukotoxin neutralizin g rabbit serum. Preincubation of the mast cells with propranolol or p- bromophenacyl bromide reduced the histamine-releasing effect of leukot oxin, while verapamil enhanced release. Experimental infection of calv es with P. haemolytica A1 reduced the total histamine content of pulmo nary mast cells recovered at postmortem. Histamine release induced by P. haemolytica leukotoxin is likely an important factor in the pathoge nesis of bovine pneumonic pasteurellosis.