Endotoxin activity and leukocytic STAT3 mRNA alterations differ according to age in lipopolysaccharide-challenged calves.

The objective of this study was to investigate the age difference in the response to endotoxin in calves related to the plasma endotoxin activity and mRNA expression of cytokines. Fifteen calves were divided into three groups: control (191 ± 21 days), weaning (162.4 ± 17.5 days), and calf (22.4 ± 8.2 days). The weaning and calf groups received 2.5 μg/kg of ultrapure O111:B4 LPS in 10 mL of each autologous serum, whereas the control calves received a similar volume of saline. Blood samples were collected at 0, 0.5, 1, 2, 4, 8, 12, and 24 h. Liver samples were collected by ultrasound-guided liver biopsy at 0, 2, 4, and 24 h. Plasma endotoxin activity was measured by the limulus amebocyte lysate kinetic turbidimetric assay. The mRNA expression level of GAPDH, TLR-4, NF-κB2, TNF-α, IL-6, and STAT3 in leukocytes and the liver was measured by real-time PCR. Following LPS challenge, the maximal plasma endotoxin activity, and leukocytic expression of TLR4, NF-κB2, TNF-α, and STAT3 were reached at 0.5, 4, 2-4, 2-4, and 4 h, respectively, in weaning and calf groups. The endotoxin activity in calf remained high until 2 h. Furthermore, the expression of leukocytic STAT3 mRNA in calf was not significantly different from the pre-value. In contrast, STAT3 mRNA in weaning markedly increased at 2 and 4 h. Therefore, this study provides new information to the literature of immune and inflammatory responses in calves.