This man does not know it but his first layer of defense, Skin, tears, saliva, mucus, stomach acid, cilia and urine. Pathogens started clashing with this line of defense. The first line of defense is always ready to block pathogens with physical barriers and chemical barriers as well.
While he rests his body is shutting down antigens and pathogens while he rests and gets on with his day to day life.
The Infection has become worse and has now entered his second line of defence, he has a fever, inflammation and his body is attacking the pathogen with white blood cells called phagocytes.
He can now tell that he has a respiratory infection and his snot is yellow, which is a sign that white blood cells have died fighting the infection and are now leaving his body.
His Infection has got even worse and is now attacking his 3rd line of defence, His body has started to make specific antibodies to attack the pathogen and shut them down. different pathogens have unique markers.
He can now go back to life as normal as his body has fought off the infection and now has cells prepared and memorized for the specific infection he has just defeated.