Researchers have shown how probiotic bacteria in the gut could undermine immunity in pancreatic cancer, pointing toward more personalized cancer treatments.

Lactobacillus — a type of bacteria thought to promote gut health — can alter the function of immune cells called macrophages in the pancreatic tumour environment and spur cancer growth, the researchers found.

«Most studies focus on positive correlations between the microbiome and cancer outcomes,» said Tracy McGaha, a professor of immunology at U of T’s Temerty Faculty of Medicine and a senior scientist at Princess Margaret Cancer Centre, University Health Network. «This work focused on negative correlations of the microbiome with cancer, and suggests that in some conditions, the constituency of the microbiome may have a negative impact.»

The journal Immunity published the results today.

Macrophages are tissue-resident immune cells thought to play an important role in tumour growth and metastasis. The researchers showed that Lactobacillus affects macrophage function by metabolizing dietary tryptophan, an essential amino acid found in protein from plant- and animal-based foods.

Indoles, a class of metabolites resulting from microbial tryptophan metabolization, activate the aryl hydrocarbon receptor, or AHR — a protein that regulates gene expression, and which can enable both beneficial inflammation and immune suppression in other areas of the body.

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Materials provided by University of Toronto. Original written by Jim Oldfield. Note: Content may be edited for style and length.