Serum interleukin-6 (IL-6) and IL-10 concentrations in normal and septic neonatal foals

Previously it was reported that compared to surviving septic foals, non-surviving foals had a 35-fold increase in interleukin-10 (IL-10) and 15-fold increase in IL-6 gene expression in their peripheral blood mononuclear cells (PBMC). As gene expression profiles can be time-consuming, we sought to determine if serum IL-6 and IL-10 in foals would aid in the diagnosis and prognosis of septicemia. A prospective study of septic neonatal foals admitted to the Cornell University Equine Hospital during 2007 and 2008 was performed. Septicemia was confirmed in 15 foals using blood culture results and sepsis scores. Blood samples for measurement of serum IL-6 and IL-10 concentrations were collected at the time of admission (T0) and again 24 (T24) and 48 (T48) hours later. Blood samples from age-matched control foals (n=15) born at the Cornell Equine Park were obtained from foals 12-72h after birth (T0) and again 24 (T24) and 48 (T48) hours later. IL-6 and IL-10 concentrations were determined in the serum from dams of septic foals and serum and colostrum from dams of control foals. Serum IL-6 was also measured in healthy foals prior to ingestion of colostrum. Interleukin-6 was detected using an ELISA and IL-10 was detected using a bead-based fluorescent immunoassay. Group differences were detected using a Wilcoxon rank sum test with a Bonferroni correction applied to the p value. There were no significant differences in serum IL-10 concentration between the two groups of foals. Relative to control foals, septic foals had significantly lower serum IL-6 concentrations at all 3 time points. Relative to septic foals, control foals had significantly higher serum IL-6:IL-10 ratios. Serum IL-6 was undetectable in foals prior to ingestion of colostrum. However, colostral IL-6 concentration measured in the control mares was high (> or =215ng/mL) in all samples suggesting passive transfer of maternal IL-6 to the equine neonate. Colostral IL-10 was undetectable in 11/12 samples. Failure of passive transfer may directly influence the serum IL-6 concentration in septic foals. Neither serum IL-6 nor IL-10 alone, were useful diagnostic indices of sepsis in equine neonates. Although the number of animals involved in this study was too small for the identification of a concrete value, the serum IL-6:IL-10 ratio is likely to provide a valuable prognosticator for neonatal septicemia.