Developmental regulation of chicken cathelicidins in the bursa of Fabricius. Bursas were harvested from broiler chickens of indicated age and subjected to RNA isolation and real-time PCR analysis of the expression of four cathelicidins. Fold differences in the cathelicidin expression level among different days after hatching were calculated relative to the expression level on day 28 using GAPDH as a reference gene. Each bar represents mean ± standard error of 3 to 5 chickens. The statistical significance was analyzed using one-way ANOVA followed by Tukey’s Test. **P < 0.01; ***P < 0.001.