S100A12 and PTX3 expression in milk from S. aureus infected cattle. Antigen capture ELISAs were used to measure the concentrations of S100A12 (a) and PTX3 (b) in milk samples taken before and 16 h after the S. aureus intramammary challenge. Data from cows 1419, 1490 and 1592 were used in the analyses. Bars represent the means ± SEM for two independent samples. The asterisk denotes significant expression difference (1 way ANOVA, P < 0.01) compared with the corresponding post-infection control sample for each cow. No PTX3 expression could be detected in milk from the intra-animal control udders or in the pre-infection samples.