In vitro modulation of tumor necrosis factor α production in THP-1 cells by lactic acid bacteria isolated from healthy human infants

• We isolated 96 strains of lactic acid bacteria from human infant feces.
• Isolates were screened for inhibition of TNF-α production by THP-1 monocytes.
• Strains inhibiting TNF-α production were Lactobacillus paracasei, Lactobacillus casei, and Weissella confusa.
• All three strains showed acid and bile tolerance.
• Metabolites within culture supernatant appear to be responsible for this effect.

The human microbiota is a source of probiotics capable of modulating the host immune system. In this study, we collected fecal samples from 100 healthy infants and isolated lactic acid bacteria which were screened for immune modulating effects on tumor necrosis factor α (TNF-α) production. Cell-free culture supernatants from 26 isolates were able to decrease TNF-α production in vitro and three of the isolates were selected as candidate probiotics (MSMC39-1, MSMC39-3, MSMC57-1). These isolates were identified using 16S ribosomal DNA sequencing as Lactobacillus paracasei, Lactobacillus casei, and Weissella confusa respectively. All three isolates were acid tolerant and bile tolerant to pH 3.0 and 4% bile respectively. Preparations of cell-free culture supernatants were processed and tested, and revealed that cell-free culture supernatants of isolates L. paracasei MSMC39-1, L. casei MSMC39-3, and W. confusa MSMC57-1 decreased the production of TNF-α significantly and were heat resistant. Only L. paracasei MSMC39-1 supernatant was proteinase-K sensitive. The effects of viable bacteria, heat-killed bacteria, and sonicated bacteria were compared. The heat-killed preparations of isolate W. confusa MSMC57-1 decreased the production of TNF-α. Sonicated cell preparations did not significantly alter TNF-α production. For isolates L. paracasei MSMC39-1 and L. casei MSMC39-3, this suggests that a substance in the cell-free culture supernatant may be responsible for in vitro cytokine modulation.