How Immune Cells Process Consumed Bacteria

Researchers from the University of Colorado Anschutz Medical Campus have made new discoveries about how immune cells process bacteria they consume. The study, published in Nature, challenges previous assumptions about bacterial storage in these cells.

The research found that macrophages, a type of immune cell, do not store consumed bacteria in specialized compartments as once thought. Instead, they break down the bacteria into essential nutrients used for protein building, energy creation, and cell survival.

Angelo D'Alessandro, co-senior author, explained, "We are what we eat. What we eat changes the composition of us and when immune cells eat bacteria the same thing happens to them."

The study revealed a critical distinction in how macrophages respond to live versus dead bacteria. Consumption of live bacteria triggers an inflammatory response, while dead bacteria do not. D'Alessandro noted, "When phagocytic cells eat dead bacteria some of the small molecules they recycle tell them not to induce inflammation, that everything is going to be fine. But when they eat live bacteria that signal is not there and it can induce inflammation which drives many diseases." 

The researchers identified key components in this process, including the mTORC1 protein complex, which regulates how macrophages utilize nutrients from consumed bacteria. They also discovered that dead bacteria contain cAMP, a molecule that potentially signals to immune cells that the bacteria are no longer a threat.

These findings have significant implications for understanding and potentially controlling chronic inflammation, which is associated with various conditions including cancer, long COVID, chronic fatigue syndrome, and shingles. D'Alessandro emphasized the importance of this research in the context of increasing antibiotic resistance, stating, "Understanding that there are brakes that nature has evolved will help us eliminate or boost this response depending on the circumstances."