Time course study of the response to LPS targeting the pig immune response gene networks

To explore individual variation in the biological response to a systemic challenge in pigs, we have developed a microarray analysis to study the kinetics of the response to a lipopolysaccharide (LPS) injection measured at 4 time points. LPS is a major component of the outer membrane in gram-negative bacteria. LPS provokes an acute inflammatory syndrome resulting eventually in all kinds of pathophysiological damages. The objective was to identify genes up- or down-regulated during the stress response triggered by LPS in the whole blood. To explore individual variation in the biological response to LPS, whole blood from 30 juvenile Large White pigs (8 weeks of age) was collected at 4 time points ( t = 0, +1 h, +4 h, +24 h) for a total of 120 samples. Each animal was injected in the neck muscles with LPS (E. coli serotype 055:B5, Sigma-Aldrich, Saint Quentin Fallavier, FR) at a dose of 15 µg/kg body weight. All pigs were females and were raised in two batches. Arrays were designed such that all observations of a single individual were kept on the same array, with two individuals (one from each batch) on one array. This design secured the kinetics of the response for each individual and prevented confounding effects between batch and array. After quality control, all 120 samples were kept for normalization and analyses.