The wild boar (Sus scrofa) lymphocyte function-associated antigen-1 (CD11a/CD18) receptor: cDNA sequencing, structure analysis and comparison with homologues

Molecular characterization and expression analysis of porcine integrins alphavbeta3, alphavbeta6 and alphavbeta8 that are potentially involved in FMDV infection

In the present study, we report the sequences and characterization of the porcine integrin cDNAs encoding alphav, beta3, beta6 and beta8 subunits and compare them to those of other species. The coding sequences for the porcine alphav, beta3, beta6 and beta8 subunits were found to be 3141, 2289, 2367 and 2304 nucleotides in length, encoding 1046, 762, 788 and 767-amino-acid-residue protein, respectively. The porcine integrin alphav, beta3, beta6 and beta8 subunit shares common structural and functional elements with their counterparts from the other species. Phylogenetic trees showed that the porcine alphav, beta3, beta6 and beta8 were clustered into the Artiodactyla group, together with those of camels, sheep, and cattle, that are susceptible to FMDV infection. Real-time RT-PCR was used to investigate expression of the integrins alphavbeta3, alphavbeta6 and alphavbeta8 in different tissues of pigs in order to determine the role of these receptors in tissue tropism. Expression analysis showed that alphavbeta6 and alphavbeta8 mRNA expression were detected at high levels in tissues known to support replication of FMDV. Tissue distribution pattern of alphavbeta3 mRNA seems to be unrelated to the known tissue tropism of FMDV. This study provided the first data of porcine integrins for the further studies of the FMDV pathogenesis in pigs.

Porcine CD18 mediates Actinobacillus pleuropneumoniae ApxIII species-specific toxicity

Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, produces Apx toxins that are recognized as major virulence factors. Recently, we showed that ApxIIIA-cytotoxic activity specifically targets Sus scrofa leukocytes. Since both LtxA from Aggregatibacter actinomycetemcomitans (aggressive periodontitis in humans) and LktA from Mannheimia haemolytica (pneumonia in ruminants) share this characteristic, respectively towards human and ruminant leukocytes, and because both use the CD18 subunit to interact with their respective LFA-1, we hypothesized that ApxIIIA was likely to bind porcine CD18 to exercise its deleterious effects on pig leukocytes. A β₂−integrin-deficient ApxIIIA-resistant human erythroleukemic cell line was transfected either with homologous or heterologous CD11a/CD18 heterodimers using a set of plasmids coding for human (ApxIIIA-resistant), bovine (-resistant) and porcine (-susceptible) CD11a and CD18 subunits. Cell preparations that switched from ApxIIIA-resistance to -susceptibility were then sought to identify the LFA-1 subunit involved. The results showed that the ApxIIIA-resistant recipient cell line was rendered susceptible only if the CD18 partner within the LFA-1 heterodimer was that of the pig. It is concluded that porcine CD18 is necessary to mediate A. pleuropneumoniae ApxIIIA toxin-induced leukolysis.