Two-edged sword....

...immune complexes.
As with all body systems, the key to homeostasis is RANGE. Too much can be as dangerous as too little....
Lymphocytes produce antibodies specific to the pathogen, which under normal circumstances engage with the rest of the reticuloendotheliel system to clear both without residua. In a variety of circumstances, though, these "immune complexes" circulate at a level that the body cannot manage. They then essentially "lodge" in places they don't belong (here, in the kidney) and cause ongoing inflammatory damage. Immune complex disease is a major problem with several autoimmune disorders (such as lupus) and a number of infections (notably hepatitis B and C).
We are, as a species, Goldilocks. Mostly our porridge and bed is just right; when they aren't, it's worse than bears!