Genetic polymorphisms and antiviral functions of porcine ficolins

Collagenous lectins, including ficolins (FCN) and mannan binding lectins (MBL) recognize glycan patterns on microbial surfaces, and single nucleotide polymorphisms (SNPs) that alter MBL expression influence susceptibility to various infectious diseases in humans and pigs. The objectives of this thesis were to characterize interactions of porcine FCN with porcine reproductive and respiratory syndrome virus (PRRSV) and to examine the associations of SNPs in FCN and related collagenous lectin genes with susceptibility to PRRSV and other common infectious diseases in pigs. Plasma-purified and recombinant porcine ficolin-alpha (FCN-alpha) bound to PRRSV particles, neutralized their cytopathic effect and inhibited replication of infectious virions in vitro, in a GlcNAc-dependent manner. Fourteen SNPs located in MBLs, FCNs or SP-A genes and thirteen SNPs located in additional innate immune genes were genotyped in 1283 healthy pigs and 464 pigs diagnosed with common infectious diseases at necropsy using MassARRAYRTM MALDI-TOF mass spectrometry. Associations with disease diagnoses and with various etiologic agents were evaluated by odds ratio comparisons and a partial least squares (PLS) method of multiple linear regression. When genotype frequencies were compared between diseased and healthy pigs, SNPs found in FCN genes were not significantly associated with disease or etiologic agent. Using a PLS statistical model, the AA genotype of FCN-alpha A(671)G was associated with high FCN-alpha mRNA expression and decreased risk for K88+ E. coli and porcine circovirus type II (PCV-2) infections. Four SNPs in the MBL2 promoter accounted for 41.5% of the variation in hepatic expression of MBL-C mRNA and were associated with enteritis, PCV-2, swine influenza virus (SIV) and Mycoplasma infections. SNPs in MBL1 and MBL2 accounted for over 40% of the variation in severity of histologically-graded PRRSV-associated pneumonia and the mutant allele of MBL2 G(-1081)A was most associated with increased susceptibility to and severity of lung lesions in PRRSV-positive pigs.;These studies provide the first evidence for antiviral activity of ficolins but did not find strong associations with disease and polymorphisms in either pig ficolin gene. However, the results suggest that polymorphisms in some collagenous lectins, especially MBL2, are markers for susceptibility to pneumonia associated with PRRSV and some other infections in pigs.