White blood cells get inappropriately tethered to vessel walls when there is damage to the inner lining of the vessels referred to as the glycocalyx. The sticky arms of the white blood cells actually penetrate through the lining of the vessels. Once this happens, a number of chemicals are released that are damaging to the vessel wall creating large pores which allow fluids to pass out of the vessel into the body tissues causing swelling and edema. I’m sure you’ve seen this. If this isn’t something your struggling with, I’m sure you know someone who is. Unfortunately, doctor’s will often dismiss this serious symptom and just put you on a water pill never getting to the destructive underlying condition. To ignore something like swelling in the feet and legs and hands is a bad idea because it can lead to other more serious conditions.
For example this condition of increased permeability of the vessels can lead to autoimmune diseases. And these are terrifying. There are over 150 recognized autoimmune diseases.