Influence of DEFB4 copy number variants on gene expression in monocytes

Beta-defensins are a group of antimicrobial peptides which also can modulate immune response. The genes coding for beta-defensins (DEFBs) on 8p23.1 formed a cluster which was affected by copy number variations (CNVs). A direct and complete analysis of the impact of DEFB4 CNV on gene expression in both mRNA and protein levels is still lacking. A cohort of 862 healthy blood donors were recruited. DEFB4 CN was screened by paralog ratio test (PRT). 66 blood donors were called back for a second blood donation. Monocytes were isolated from peripheral blood and stimulated by LPS. DEFB4 mRNA and coding protein (beta-defensin 2) were measured by qPCR and ELISA, respectively. DEFB4 CN was accurately determined by droplet digital PCR (ddPCR). The correlation between DEFB4 CN and expression levels including mRNA and protein was analysed. DEFB4 mRNA was not detectable without stimulation in primary monocytes and was induced after stimulation with LPS. Beta-defensin 2 was detectable in freshly isolated monocytes. After stimulation with LPS, beta-defensin 2 was strongly induced and the level was significantly higher than that of non-stimulated controls (100.10 ± 33.17 ng/ml vs. 33.68 ± 10.40 ng/ml, P < 0.0001). A significant correlation between DEFB4 CN and mRNA expression level was found (P < 0.05, r = 0.25). However, no correlation between DEFB4 CN and protein expression including baseline level and the level after stimulation was found (P > 0.05). DEFB4 CNV has an impact on gene expression in mRNA but not protein level in monocytes.