Porcine alveolar macrophage Mac-1 (CD11b/CD18) adhesion molecule expression

The adhesion molecule Mac-1 plays an important role during leukocyte recruitment into inflammatory sites and also serves as a complement receptor type 3 (CR3). Mac-1 is a noncovalent heterodimer consisting of an α-chain (CD11b) and a β-chain (CD18). We report the cloning and sequencing (GenBank accession number U40072) of the porcine CD11b cDNA using the reverse transcriptase-polymerase chain reaction (RT-PCR). Porcine CD11b cDNA and deduced amino acid sequences demonstrated 84% and 80% sequence identity, respectively, with human CD11b. The 4.7 kb porcine CD11b transcript was also similar to the size of the human CD11b transcript. Northern blot analyses detected CD11b transcripts in spleen cells and peripheral blood leukocytes, but not in lung lavage cells. In contrast to Northern blot results, 72% of freshly isolated alveolar macrophages stained positive using a cross-reactive antihuman CD11b antibody (TMG6-5). Compared to spleen and peripheral blood cells, alveolar macrophages expressed the highest levels of CD18 mRNA. Using anti-CD18 monoclonal antibodies which cross-react with porcine CD18, two different porcine CD18 epitopes were identified by flow cytometric antibody competition assays. However, the majority of the anti-CD18 antibodies tested competed for the same CD18 epitope. Mac-1 expression in porcine alveolar macrophages was not altered at either the mRNA or surface expression level by inflammatory stimuli, including fMLP, PMA, LPS, hIL-1α, hIL-6, hTNF-α, and hIFN-γ.