Social Rank Influences the Distribution of Blood Leukocyte Subsets in Female Growing Pigs
The effect of high (DOM) and low (SUB) social rank on blood immune variables was examined in female growing pigs. Pigs were mixed with unfamiliar pigs at 9 weeks of age and kept in stable groups of 4 pigs for 5 weeks. Social rank was determined using a feeding competition test. SUB pigs showed reduced growth as compared to DOM pigs confirming their lower social status. Blood was sampled for immunological assessments immediately before grouping the pigs and again after the 5 weeks of social housing. White Blood Cell (WBC) counts, percentage of CD4 positive cells (CD4+), percentage of CD8 positive cells (CD8+), percentage of swine leukocyte antigen II (SLAII) carrying cells, LPS-stimulated Toll-like Receptor 4 (TLR4) expression, and LPS-stimulated tumor necrosis factor-alpha (TNF-) responsiveness were determined at both times. IgG and IgM concentrations were measured following the 5 weeks of social housing only. From the WBC counts it was found that the percentage of neutrophils was higher in SUB pigs and the neutrophil to lymphocyte ratio was higher in DOM pigs. The percentage of CD4+ cells decreased with time in both DOM and SUB pigs, but only significantly in SUB pigs. The percentage of CD8+ cells was higher in SUB pigs than in DOM pigs and decreased with time in both DOM and SUB pigs. In addition, SUB pigs had a higher ex vivo TNF- responsiveness as compared to DOM pigs. Both the percentage of SLAII carrying cells and LPS-stimulated TLR4 expression increased with time, but here no significant effect of social rank was found. In addition, neither IgG nor IgM concentrations showed any relationship with social rank. The findings indicate that social rank influences the distribution of blood leukocyte subsets in female growing pigs, suggesting that the pig would be a good model for investigating the effects of long-term immunomodulation on health.