In situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in calves with acute Pasteurella haemolytica pneumonia

The in situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA i n normal and pneumonic lung tissues of Holstein calves with bovine leukocyt e adhesion deficiency (BLAD) was compared with that of age-matched non-BLAD Holstein calves by in situ hybridization. Twenty-four Holstein calves (bot h BLAD and non-BLAD) were randomly assigned to one of two experimental grou ps and inoculated intrabronchially with Pasteurella haemolytica or pyrogen- free saline. Lung tissues were collected and fixed in 10% neutral formalin at 2 or 4 hours postinoculation (PI). The expression and distribution of IC AM-1 mRNA in the different cell types of the lung tissue was detected by in situ hybridization with a 307-base-pair bovine ICAM-1 riboprobe. In lungs of both non-BLAD and BLAD saline-inoculated calves, ICAM-1 expression was p resent in epithelial cells but occurred in <30% of cells in bronchi, bronch ioles, and alveoli. ICAM-1 expression in vascular endothelial cells was pre sent in <30% of cells in pulmonary arteries and veins. The expression of IC AM-1 was significantly greater (>60% of cells) in bronchiolar and alveolar epithelial cells and pulmonary endothelial cells of arteries and veins in b oth BLAD and non-BLAD calves inoculated with P. haemolytica. Bronchiolar ep ithelium had the highest intensity of mRNA expression and highest percentag e of cells that were stained, whereas bronchial epithelium had the lowest i ntensity and percentage of cells stained. Most alveolar macrophages and neu trophils in infected lungs also expressed ICAM-1. ICAM-1 expression was gen erally increased in infected BLAD calves at 2 hours PI as compared with non -BLAD calves but not at 4 hours PI. The increased expression of ICAM-1 duri ng acute P. haemolytica pneumonia in calves suggests that ICAM-1 is upregul ated and may play a role in leukocyte infiltration. The extent of ICAM-1 ex pression in P. haemolytica-inoculated calves with BLAD was initially enhanc ed but otherwise similar to that in non-BLAD calves.