Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 1996
Publication Date: N/A
Interpretive Summary: Pneumonia is a common problem in cattle, swine, and other animals raised for food production. The problem decreases profits of producers and leads to condemnation at slaughter. Pneumonia is often caused by microorganisms such as bacteria that colonize the airways and the lung. Bacteria evoke a response by immune cells of the blood that enter the lung in an attempt to eliminate the infection. In this work, we studied passage of one type of white blood cell, the neutrophil, into the lung shortly (4-6 hours) after infection with a bacteria. One set of cattle had normal neutrophils; the other set had neutrophils with a particular molecular defect. The defect is genetic and results in neutrophils with impaired expression of the CD18 molecule. CD18 is vital for many neutrophil functions; the role of CD18 in passage of neutrophils into the lung during pneumonia is poorly understood. In this study, we found that neutrophils lacking CD18 may have impaired passage into the lung. Future studies should be aimed toward identifying compounds that enhance neutrophil infiltration into the lung. Compounds that increase passage of neutrophils lacking CD18 may be especially useful for optimizing neutrophil entrance. Compounds that decrease neutrophil infiltration may be useful as well for particular problems such as acute lung injury (seen with toxins, etc.). This work can be extrapolated to other animal species and, therefore, is beneficial to animals that develop pneumonia, including swine.
Technical Abstract: CD18 is a subunit for three beta 2 integrin molecules (MAC-1, p150,95, LFA-1) which are expressed on the plasma membrane of neutrophils. In most tissues, those molecules mediate passage of neutrophils into sites of infection. To determine whether CD18 is vital for passage through the pulmonary alveolar wall, lung lobes of cattle with neutrophils that were deficient in CD18 expression (CD18-) and cattle with normal CD18 expressio (CD18+) were inoculated with Pasteurella haemolytica by fiberoptic bronchoscopy. Neutrophil passage into alveolar lumens at 4 and 6 hours post-inoculation was measures by computerized image analysis of histologic sections. Total numbers of neutrophils in alveolar lumens of the two groups were similar; however, increased numbers of neutrophils were present in the alveolar wall of CD18- cattle. These cattle also had a higher resting number of neutrophils in the alveolar wall. This work shows that higher numbers of CD18- neutrophils remain in the alveolar wall. This increase may be due to impaired passage or increased numbers of neutrophils in the pulmonary capillaries.