So respiratory viruses like the cold, flu, and covid enter the body through the nasal passages and not through the blood stream. Since the white blood cells are in the blood stream, how do they get to the virus to fight it?
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You blood vessels feed capillaries, much smaller tubes that worm their way into all your tissues. At the very end, blood cells must cross through the tissue and back into another capillary that returns them to the main circulatory system.
The red cells have to get within touching distance of just about every cell so that they can deliver oxygen, so at the cellular level all your tissues are webbed with these capillaries.
The immune cells also patrol this network, and will stop and linger in one location if they’re “flagged down” by a cell in distress.
When one of your cells gets infected by a virus, it attempts to self destruct and spew warning chemicals out to alert all the immune cells nearby.
Some particularly devious viruses can disable this mechanism, it’s a constant evolutionary battle.
It’s actually a misconception that white blood cells are in the blood stream, they’re everywhere, in blood and living dormant in tissues. So immune cells can attack things in their neighborhood—and the airway is chock full of resident immune cells
Certain types of white blood cells in the blood also know how to stick onto bacteria and viruses, and when they do, others are attracted to and begin sticking to the original guy, which can build an immune response.
I’m going really ELI5 here but it beats the insane language that immunologists use to describe things
Your respiratory infection symptoms are your immune system fighting the virus at those sites! So you have layers of protection in your nose/throat/lungs similar to your skin (mucosa), but with coats of mucous/secretions to help keep things wet. You also have white blood cells (WBCs) on the surface of this mucosa that are always on the hunt for infected cells.
When a virus lands on a cell in your nose, it goes inside of that cell, makes a bunch of copies, then explodes out to infect nearby cells. This goes on until WBCs show up to clean up the mess, and in doing so they pull the fire sprinkler system and cause all of the other healthy cells to make *lots of mucous* to trap the virus and get rid of it (by leaking out of your nose or down the back of your throat where it’s swallowed into the acid-pit that is your stomach).
When a virus lands in your lungs, the exact same thing happens, only this time the fire sprinkler system is thicker and causes you to cough. When you cough, you move this thicker mucous up through your lungs and up into your mouth where it’s either spit out or swallowed. Same goal though – get the bad stuff out.
[Here’s a neat video](https://www.youtube.com/watch?v=B9Qi7we0Ynk) that shows neutrophils (a kind of WBC) and how they move around the blood stream and wiggle their way through vessel walls into surrounding areas – this is how they can get to surface spots like in the nose/lungs.
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