Evaluation of the effect of probiotic bacteria Lactobacillus acidophilus PTCC1643 and Lactobacillus casei PTCC 1608 on the TLR2 and TLR4 expression in HT29 cells infected with Salmonella enteritidis

Probiotics are living organisms that are beneficial for human health. Lactobacillus species has been considered as probiotic bacteria due to their adjustment of human immune responses and therapeutic effects in inflammatory disorders. The aim of the present study was to evaluate the effects of Lactobacillus probiotic strains on toll-like receptors (TLR2 and TLR4) expression in HT29 cell line (a human colon cancer cell line) infected with S. enteritidis. This experimental study was done in Food Microbiology Research Center of Tehran University of Medical Sciences, Iran, from March 2016 to February 2017. In this study, two strains of Lactobacillus acidophilus PTCC 1643 and Lactobacillus casei PTCC 1608 were used. HT29 cells were cultured in RPMI medium containing fetal bovine serum and antibiotics. Then, the cells were treated with the Lactobacillus strains, after or before challenge with S. enteritidis. After total RNA extraction and cDNA synthesis, the capacity of probiotic lactobacilli to modulate TLR2 and TLR4 expression on treated and un-treated HT29 cells were assessed quantitatively using Real-time polymerase chain reaction technique with specific primers. Our findings indicated that after treatment of non-infected HT29 cells, with both the probiotics, the expression of TLR2 and TLR4 genes significantly increased. In contrast, the expression of these two genes in HT29 cells which were infected with S. Enteritidis was significantly reduced before and after treatment with each one of the probiotic bacteria. The anti-inflammatory effect of probiotic lactobacilli on S. enteritidis were confirmed in tests. This study showed that L. acidophilus and L. casei play a major role in boosting the innate immune responses, the TLR2 and TLR4 expression levels also decreased, pre and post-infection with S. enteritidis. According to the results, both Lactobacillus strains have remarkable anti-inflammatory effect in pathogenicity of S. enteritidis, but L. acidophilus display greater anti-inflammatory activity than L. casei in this work. Additional in vivo and in vitro studies are required to further elucidate the mechanisms underlying this anti-inflammatory effect.