Porcine mannan-binding lectin A binds to Actinobacillus suis and Haemophilus parasuis

Various collagenous lectins involved in innate immunity bind to surface oligosaccharides of bacteria and other microorganisms. We have been characterizing porcine plasma lectins that bind in a carbohydrate-dependent manner to surfaces of important bacterial pig pathogens including Actinobacillus suis (AS), A. pleuropneumoniae (APP), and Haemophilus parasuis (HP). A plasma protein with 32 kDa subunits (pI 5.4 and 5.75) bound most isolates of HP, AS, and some APP. Partial amino acid sequences of this protein were similar to mammalian mannan-binding lectins (MBLs). The corresponding MBL-A cDNA sequences obtained by RT-PCR on liver tissue from pigs and cattle were homologous to the MBL1 gene of mice, rats and the MBL1P1 pseudogene of humans and chimpanzees. While human MBL-C, the product of the MBL2 gene, is known to bind various microorganisms, our studies in pigs provide the first direct evidence that MBL-A has bacteria-binding properties, and suggest it may have antibacterial functions in pigs.