Type III hypersensitivity is where I started to lose track of how to keep them separate. I is allergies and done with IgE. II was antibody mediated and IgM and IgG. III is an antigen-antibody complex, so this is the first time we’re really forming a complex of more than one thing.
It’s not unusual for these complexes to become formed. What goes wrong is that for one reason or another macrophages don’t completely clear them and we have leftover complexes. They then get deposited on membranes, like the surface of blood vessels. That activates the complement system which leads to tissue destruction. The typical timeline for this is in the weeks area.
Some samples here are Poststreptococcal glomerulonephritis, Serum sickness and Systemic lupus erythematosus. Actually, SLE would be a good one to do as a solo article. Maybe look for that coming up.
However, without going into specifics of each disease, that should cover you for type III hypersensitivity!
Short, but it works!