What is Immunity
The human body, which is composed of more than 30 trillion cells*, is constantly exposed to the risk of invasion by various foreign substances such as harmful bacteria and viruses. Immunity is the biological defense system that prevents the invasion of foreign substances and detects and eliminates them from the body. The word immunity originated from the Latin words immunitus (remission of taxes, exemption) or immunis (exempt from service or tax), and the word immunity has now also come to mean avoiding epidemics (infectious diseases).
Immunity is broadly divided into “Innate Immunity” and “Adaptive Immunity.”
Humans are born with innate immunity and it is mostly mediated by phagocytes (which engulf foreign bodies such as bacteria) including neutrophils, macrophages, and dendritic cells, and natural killer cells. These cells have receptors that distinguish self from non-self and attack bacteria and viruses (pathogens) that have invaded the body.
A mechanism that memorizes bacteria and viruses that have invaded the body, and then reacts and attacks when the same pathogen invades again; it functions by obtaining information about foreign substances from innate immunity. There is cell-mediated immunity in which T cells play a leading role and humoral immunity in which B cells play a major role. In humoral immunity antibodies mainly eliminate target cells such as cancer cells and viruses. Therapeutic antibodies have been developed by applying this function to produce a wide range of antibodies to help cure diseases.