Influence of β2-Integrin Adhesion Molecule Expression and Pulmonary Infection with Pasteurella haemolytica on Cytokine Gene Expression in Cattle

Abstract

<p>β₂-Integrins are leukocyte adhesion molecules composed of alpha (CD11a, -b, -c, or -d) and beta (CD18) subunit heterodimers. Genetic CD18 deficiency results in impaired neutrophil egress into tissues that varies between conducting airways and alveoli of the lung. In this study, we investigated whether CD18 deficiency in cattle affects proinflammatory cytokine (PIC) expression in pulmonary tissue after respiratory infection with <em>Pasteurella haemolytica</em>. Cattle were infected with <em>P. haemolytica</em>via fiberoptic deposition of organisms into the posterior part of the right cranial lung lobe. Animals were euthanized at 2 or 4 h postinoculation (p.i.), and tissues were collected to assess PIC gene expression using antisense RNA probes specific for bovine interleukin-1α (IL-1α), IL-1β, IL-6, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) along with the β-actin (β-Act) housekeeping gene. Expression of PIC was induced at 2 h p.i. in <em>P. haemolytica</em>-infected cattle and continued to 4 h p.i. At 2 h p.i., induction of gene expression and increase of cells that expressed PIC were observed both in CD18⁺ and CD18⁻cattle after inoculation of<em>P. haemolytica</em>. The induction of gene expression with<em>P. haemolytica</em> inoculation was more prominent in CD18⁻ cattle than in CD18⁺cattle by comparison to pyrogen-free saline (PFS)-inoculated control animals. At 4 h p.i., however, the induction of PIC, especially IL-1α, IL-6, and IFN-γ, in the lungs of CD18⁺ cattle inoculated with<em>P. haemolytica</em> was greater than that in lungs of the CD18⁻ cattle. IFN-γ and TNF-α genes were not increased in <em>P. haemolytica</em>-inoculated CD18⁻ cattle lungs compared to the PFS-inoculated control lungs at 4 h p.i. In PFS-inoculated lungs, we generally observed a higher percentage of cells and higher level of gene expression in the lungs of CD18⁻cattle than in the lungs of CD18⁺cattle, especially at 4 h p.i. The rate of neutrophil infiltration into the lungs of CD18⁻ cattle at 2 h p.i. was significantly higher than that of CD18⁺ cattle; at 4 h p.i., there was no difference between the two groups. These data suggest that β₂-integrins may contribute to the induction of expression of some PIC genes, as a consequence of <em>P. haemolytica</em> infection.</p>