CHICAGO, Feb. 14 (Xinhua) -- Northwestern University (NU) and University of Washington researchers have uncovered that immune cells count their neighbors before deciding whether or not the immune system should kick into high gear.

The researchers examined macrophages, a type of immune cell that is part of the first line of defense for combatting infection and disease. They observed how macrophages responded to a chemical produced by bacteria, a red flag that alerts the body to the presence of infection, using techniques that enabled them to watch individual cells' responses over time. They then used computational models to help interpret and explain these observations.

"Over time, the cells observe their surroundings to get a sense of their neighbors," said first author Joseph Muldoon, a graduate student in NU's Interdisciplinary Biological Sciences Graduate Program. "Each cell becomes poised to respond as a high activator or not."

"It's especially interesting because the immune system is decentralized," Muldoon said. "Immune cells are individual agents that need to work together, and nature has come up with a solution for how they can get on the same page. Cells arrive at different activation states, but in such a way that, on the whole, the population response is calibrated."

The researchers believe this information could be used to help design better drugs as well as to guide the engineering of advanced cell-based therapies.

The body's immune system is constantly working to maintain a delicate balance. When a threat is introduced, the system needs to respond strongly enough to fight off infection or disease but not so strongly that it causes harm.

"When it comes to immune responses, it's the difference between life and death," said Joshua Leonard, an associate professor of chemical and biological engineering at NU's McCormick School of Engineering. "If your body over-responds to a bacterial infection, then you could die from septic shock. If your body doesn't respond enough, then you could die from rampant infection. Staying healthy requires the body to strike a balance between these extremes."

The research was published Thursday in the journal Nature Communications. Enditem

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