The chemical barriers include tears and saliva which contain an enzyme that breaks down the cell wall of many bacteria. Those that are not killed immediately are trapped in mucus and swallowed. Special cells line and protect the nose, throat and other passages within your body. Another is stomach acid that kills bacteria and parasites that have been swallowed.
White blood cells can can find, kill and ingest pathogens seeking an entrance into the body.
Inflammatory response is a fundamental type of response by the body to disease and injury. It is how your body recognizes and defends itself.