The scientists used fruit flies as a model as they can be standardized for environmental factors. The flies can be modified with distinct genetic profiles while keeping environmental factors the same and were infected with an intestinal bacterium. The researchers used over a hundred fruit fly strains with well-defined differences in their sets of genes.
They discovered that there was a striking variation across the susceptibility of different strains. One strain would show 100% susceptibility to the bacterium (all the flies would die after three days), in another there would be 100% survival, and all others fell somewhere in between (e.g. 50-50 survival etc). The genes are linked to the production of highly reactive molecules that neutralize infectious microorganisms.
“It has to be the genome,” said Bart Deplancke, since all environmental factors such as food, temperature etc. were the same across the strains. “Just having slight differences in the genome can make you anywhere from completely resistant to completely susceptible to an infection.”
The immune response of these group of genes assists by resisting infections by lowering the activity of reactive oxygen species, minimizing their potential damage to the gut. The group of genes also helps with faster clearance of infectious pathogens and higher stem cell activity for tissue healing. The body may produce adverse health effects based on the gut immune response from the cluster of genes as the inability to repair damaged tissue and clear pathogens from the gut may lead to chronic gastrointestinal diseases.
“Our work shows how relatively minor, but systematic variation in a fly’s — and probably a human’s — genome can lead to wide differences in the susceptibility of the gut to infections, said Bart Deplancke.”
People are not equal in terms of gut immunity and previous studies have revealed a metabolic signalling pathway from gut bacteria that affect the immune response. Some individuals are more susceptible to infections than others, even when they share similar diets.
Maroun S. Bou Sleiman, Dani Osman, Andreas Massouras, Ary A. Hoffmann, Bruno Lemaitre, Bart Deplancke. Genetic, molecular and physiological basis of variation in Drosophila gut immunocompetence. Nature Communications, 2015; 6: 7829 DOI:10.1038/ncomms8829