Kinetics of the activation of immune markers in vitro in response to A. pleuropneumoniae infection. H2O2 (A) and TNF-α (B) production were measured after in vitro stimulation of blood leukocytes with PMA (for A) or inactivated A. pleuropneumoniae (for B). (C) Basal expression of TNF-α by BALF leukocytes after 6 h cultivation in vitro. The expression of the specific markers was recorded as shown on the bottom of the graph for each breed at 7 days before infection (-7) as well as at 4 and 21 days after infection. The box represents the 50% between 25% and 75% quartiles. The line inside the box indicates the median. The top and bottom lines denote the 5 and 95 percentile, whereas the black crosses denote minimum and maximum values. The numbers on the top of the boxes indicate the number of samples examined. ND – not determined; * p < 0.05; ** p < 0.01; *** p < 0.001.