CpxR regulates the expression of T6SS2 genes in APEC. A The transcription levels of T6SS2 core genes were analyzed by qRT-PCR. B The levels of Hcp2B in APEC strains were confirmed with Western blotting. C qRT-PCR analysis for the transcriptional levels of the T6SS2 genes hcp2B, vgrG and xmtU in the absence or presence of NlpE in the wild-type and mutant strains. D The levels of Hcp2B in APEC strains with or without NlpE overexpression were determined by Western blotting. The qRT-PCR data are shown as relative expression ratios compared with that of the wild-type strain. For Western blotting, anti-DnaK antibody was used as a control. The expression of the Hcp2B protein was determined by quantifying the grayscale in Image J software. Two-way ANOVA was carried out to determine statistical significance (*P < 0.05; ***P < 0.001).