Vasculitis

The Immune System's Friendly-Fire Traffic Jam

Imagine your blood vessels are a network of highways with three-layer walls (asphalt bottom, steel-reinforced middle, painted lane-markers on top). Normally, traffic flows smooth because the inner layer is slick like fresh asphalt. But in vasculitis, the immune system mistakes the highway wall itself for an enemy invader—like security guards thinking the concrete support beam is a bomb. They swarm in, throw roadblocks (inflammation), and literally tear chunks out of the middle-layer steel. Some highways narrow to a one-lane bottleneck (stenosis), starving towns downstream of deliveries (ischemia). Others develop weak spots where the steel is eaten away, causing the wall to balloon or burst (aneurysm or rupture). The red or purple splotches you see on skin are like blood leaking from a punctured water pipe buried under the asphalt—the guard-cell attack has weakened the tiny town-street pipes so badly they weep.