system
Given the following post, respond as if you're commenting on Reddit:
human
How does the immune system work outside the bloodstream?

I know we have white blood cells and other immune cells floating around in our bloodstream that attack pathogens, but how do our bodies fight infections that occur outside the blood vessels?
gpt
Cells from the immune system inhabit every single tissue in your body, not just the blood stream. They can move around as well.

In addition to this, the local blood vessels can open up to allow liquid and immune cells (and supporting proteins) to invade the infected tissue, to help with the immune response.

This mostly happens in response to cells giving off chemical signals when they detect an infection.