Answer :
Our body has many cells that protect us from diseases though our whole body has an arsenal to protect itself from pathogens and other various diseases. WBC or white blood cells or the anti-bodies are the cells which fight for us, in order to kill the disease or infection it needs to be quick and needs to detect viruses, diseases, and various infections rapidly therefore, the doctors sometimes use harmless viruses for the WBCs to work faster so, our body temperature rises during the struggle between our WBCs and foreign cells(diseases) . Fact:- A baby can't protect itself from diseases therefore the mother's milk contains anti-bodies to protect it from pathogens and deadly diseases.
When there is an infection our WBC's fight against the infection causing germs and these germs are not able to grow in high temperatures therefore our body temperature rises to prevent them from further multiplication while our WBC's are fighting them off.
Hope i helped u:)
Hope i helped u:)