Determination of tumor necrosis factor-α responsiveness in piglets around weaning using an ex vivo whole blood stimulation assay

Ex vivo whole blood stimulation with endotoxin has proved to be a useful method for quantitative evaluations of the pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) response ability in humans. In the present study, a dose- and time-response study was carried out in order to develop an ex vivo whole blood stimulation assay for the quantification of TNF-α production in pigs. The TNF-α response was enhanced with increasing endotoxin stimulation dose. The maximum TNF-α response occurred after 2–8 h of stimulation. Subsequently, the assay was used to evaluate the TNF-α response in pigs ( n = 32) in relation to weaning. The TNF-α response was 332 pg ml −1 (±59 pg) plasma 2 days before weaning and 127 pg ml −1 (±23 pg) plasma 2 days after weaning, which was a significant reduction ( p < 0.001). Total and differential counts of leucocytes were the same before and after weaning. Thus the lower TNF-α response may be due to reduced monocyte responsiveness to the endotoxin, rather than caused by a reduction in monocyte numbers. The reduced TNF-α response in piglets after weaning may be a factor of importance to the increased disease susceptibility seen in piglets in this period.