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An Orderly Swarm

Bacteria-fighting neutrophils swarming to the site of infection self-limit their numbers

14 August 2021

An Orderly Swarm

The immune system prowls the body looking for a fight. When its abundant foot soldiers, neutrophils, encounter a threat they attack the invading microbe and call for backup, which arrives in large numbers, each reinforcement also calling for more. This swarm of support mounts an effective defence, but left unchecked could cause collateral damage, like superheroes wrecking buildings while defeating villains. A new study has visualised the process in mice (pictured, falsely coloured neutrophils forming a red cluster over time) and revealed that the swarming neutrophils become insensitive to their own secreted alarm signals once concentrations become high enough. In experiments where this stop mechanism was blocked, excessive swarming set in which counterintuitively reduced the swarm’s effectiveness. A measured, regulated swarm was best equipped to fight off infection. Understanding the order beneath the swarm’s chaos is key to understanding the body’s defence mechanisms, and may help turn them to therapeutic benefit.

Written by Anthony Lewis

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