COVID-19 can derange the immune system in complex ways, research shows. Here's how.

There’s a reason soldiers go through basic training before heading into combat: Without careful instruction, green recruits armed with powerful weapons could be as dangerous to one another as to the enemy.

The immune system works much the same way. Immune cells, which protect the body from infections, need to be “educated” to recognize bad guys — and to hold their fire around civilians. 

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