MOLECULAR-CLONING AND CHARACTERIZATION OF THE PORCINE CD18 LEUKOCYTE ADHESION MOLECULE

Leukocyte adhesion molecules play an important role in regulating immu nocyte trafficking into peripheral tissues. CD18 is the common beta-ch ain of the beta(2)-integrin class of leukocyte adhesion molecules, Por cine CD18 cDNA was cloned using reverse transcriptase-polymerase chain reaction (RT-PCR), subcloned, and sequenced (GenBank accession number U13941). The deduced 769 amino acid sequence for porcine CD18 contain s a 22 amino acid signal sequence, a cysteine-rich domain, and a 23 am ino acid transmembrane domain. Porcine CD18 showed 79.3% cDNA sequence identity and 83.2% amino acid sequence identity with human CD18. Nort hern blot analysis revealed that porcine CD18 mRNA was expressed const itutively at high levels in freshly isolated alveolar macrophages, and levels declined approximately 50% over a 12 hr culture period. Periph eral blood cells and spleen cells expressed lower amounts of CD18 mRNA . Anti-human and anti-canine CD18 antibodies were tested for xeno-reac tivity against porcine CD18, and more than 62% freshly isolated unstim ulated alveolar macrophages were stained with anti-CD18 antibodies. Po rcine macrophage CD18 transcript levels and cell surface expression de tected by flow cytometry were not significantly altered following stim ulation with LPS or human proinflammatory cytokines, including interfe ron-gamma (IFN-gamma), interleukin-alpha. (IL-1 alpha), IL-1 beta, tum or necrosis factor-alpha (TNF alpha), and IL-6. Thus, CD18 gene expres sion by porcine alveolar macrophages appears not to be regulated by hu man proinflammatory cytokines. These reagents may be useful for studyi ng the role of adhesion molecules in the immunobiology of porcine mode ls of allo- and xenotransplantation.