BackgroundEpigenetic studies have shown that low‐birth‐weight (LBW) and growth restriction has been associated with reduced immune function in humans and reduced passive immunity in pigs. To examine the immune responses of high‐birth‐weight (HBW) and LBW groups of pigs, influenza A virus infection was used as an exemplifier of neonatal respiratory disease.ObjectivesThe objectives of this study were (i) to compare clinical, immunological, and pathological outcome of influenza infection in HBW to LBW pigs and (ii) to establish standardized sampling sites, score each site independently with set criteria, and compare scores between sites.MethodsSixty‐eight 4‐week‐old pigs originating from either HBW or LBW litters were intratracheally inoculated with 106·3 TCID 50/ml of A/swine/Texas/4199‐2/1998 H3N2 and euthanized 48 hours later. Samples were collected 2·5 cm from the tip of both cranial and middle lung lobes. The formalin‐fixed paraffin‐embedded tissue sections were scored in a blinded manner by a single pathologist using established scoring criteria for routine and immunohistochemical stains. Clinical parameters, lung and nasal swab virus titers, and cytokine levels for interferon‐alpha and interleukin‐1‐beta, IL‐6, and IL‐8 were measured.Results and ConclusionsLung lesion severity and influenza staining intensity were significantly lower in LBW compared with HBW pigs (P < 0·05). Additionally, examining just the LBW group, the significant difference between lobes (P = 0·009) showed that the mean score for the right cranial lung lobe was higher compared with the other three lobes.

Influenza viruses are a common cause of respiratory disease in swine. Infections range in severity from asymptomatic to causing significant morbidity. The main objective of this study was to compare lung transcriptomic and epigenetic responses to influenza infection in pigs from high or low birth weight litters. The latter is a potential indicator of intrauterine growth restriction, a significant risk factor for prenatal programming effects. Individual pigs from high (HBW) or low birth weight (LBW) litters (n = 17) were inoculated with influenza A virus and euthanized 48 hours later. Lesion severity and viral loads were assessed as previously described. The transcriptional response to infection in LBW and HBW groups (n = 16) was assessed by microarray. A separate analysis of pigs classified as ‘Resilient’ (RES) or ‘Susceptible’ (SUS) (n = 6) on the basis of severity of lung pathology was also conducted. Eight genes were confirmed as differentially expressed for the birth weight comparison, including three antiviral genes with lower expression in LBW: ISG15, OAS1, and OAS2 (P<0.05). The promoter region methylation status of these three genes was assessed for each birth weight group, and no differences were found. These expression data are consistent with our previous finding that LBW pigs had less severe lesion scores and a trend towards lower viral titres in lung than the HBW cohort. The SUS v RES comparison identified 91 differentially expressed genes (FDR<0.05) that were enriched with functional annotation terms and pathways associated with inflammation. The cytokine genes IL6, IL8, and CCL2 were all upregulated in SUS pigs, and may have driven disease severity in these animals. In conclusion, this study found no evidence that the transcriptional immune response to influenza was adversely affected by low litter birth weight, but did identify several candidate genes for driving disease pathology.