Comparison of TLR4 Genotype and TLR4 Pathway-Related Cytokines in Different Strains of Mice in Response to Pertussis Toxin Challenge

Background: The genetic background of Toll-like receptor 4 (TLR4) proved to be important in the induction of immune protection against Bordetella pertussis infection in humans. Currently, the evaluation of the acellular pertussis (aP) vaccine depends largely on using different mouse strains, while the TLR4 genotype of different mouse strains in response to pertussis toxin (PT) is not carefully determined. The current study was designed to determine the differences in TLR4 genotype and TLR4 pathway-related cytokines in response to PT stimulation among mouse strains of ICR, NIH, and BALB/c. Method: We first determined the single-nucleotide polymorphisms (SNPs) in the TLR4 gene by using first-generation sequencing. Then, the cellular response, including the TLR4 mRNA expression and TLR4 signaling-related cytokines, of immune cells from different mouse strains after PT stimulation was determined. Result: Three missense mutation sites (rs13489092, rs13489093, rs13489097) of the TLR4 gene were found. ICR mice were homozygous without mutation, NIH mice were partially heterozygous, and BALB/c mice were homozygous with a missense mutation. The expression of TLR4 was repressed while the downstream cytokines were upregulated after PT stimulation differently among mouse strains. The IFN-β cytokine of the TRIF pathway was significantly increased in ICR mice (p < 0.05). The IL-6 cytokine of the MyD88-dependent pathway was significantly increased in BALB/c mice (p < 0.05). The identified SNPs of the TLR4 gene in different mouse strains might account for the differences in cytokines levels determined after PT stimulation. Conclusions: Our studies might provide useful referees to reduce the mouse-derived difference in the determination of vaccine titer and increase the comparability of the vaccine from different origins, as different mouse strains were used for vaccine development in different countries.