This study aimed to examine how probiotics affect autophagy and interleukin-1β (IL-1β) expression in Salmonella-infected intestinal epithelial cells (IECs). The original Caco-2 cells and ATG16L1 siRNA-transfected Caco-2 cells were pretreated or left untreated with probiotics, including Lactobacillus rhamnosus GG (LGG; ATCC 53103) and Bifidobacterium longum (BL; ATCC15697), and these cells were infected with wild-type Salmonella enterica serovar Typhimurium (S. Typhimurium strain, SL1344). Western blot analysis was used to detect the conversion of microtubule-associated proteins 1A/1B light chain 3B (LC3)-I to LC3-II. Immunofluorescence was used to analyse LC3⁺ autophagosomes. Membrane proteins were analysed by western blot for protein (ATG16L1, NOD2), and total RNA by RT-PCR for mRNA expression [ATG16L1, vitamin D receptor (VDR)]. We demonstrated that probiotics enhanced both VDR mRNA, and nucleotide-binding oligomerisation domain-containing protein 2 (NOD2) and autophagy-related protein 16-like 1 (ATG16L1) protein expression. The enhanced expression resulted in autophagic LC3-II protein expression and formation of LC3 punctae in Salmonella-infected Caco-2 cells. It was observed that ATG16L1 siRNA could attenuate this mechanism, and ATG16L1-mediated IL-1β expression was suppressed by probiotics. These results suggest that probiotics enhance autophagy and also suppress inflammatory IL-1β expression in Salmonella-infected IECs via membrane ATG16L1 protein expression. Probiotics may enhance autophagic clearance of Salmonella infection and modulate inflammatory responses to protect the hosts. Hence, we can assume that probiotics could treat infectious and autoimmune diseases through mechanisms involving ATG16L1.

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