The applications of immune mechanisms in medicine include vaccination(vaccines) and serum therapy. Let us learn their principles, including mRNA vaccines for COVID-19.
Basic Knowledge
Vaccination(vaccines) is a method in which an antigen whose pathogenicity has been weakened or eliminated(vaccine) is administered to the body in advance to create memory cells. When the actual pathogen enters, it can be dealt with quickly through a secondary response.
Types of vaccines:
① Live vaccines(weakened pathogens: measles・rubella・BCG・chickenpox)
② Inactivated vaccines(killed pathogens: influenza・Japanese encephalitis)
③ Toxoids(detoxified toxins: tetanus・diphtheria)
④ mRNA vaccines(genetic information for making pathogen proteins is administered: put into practical use for COVID-19)
⑤ Viral-vector vaccines(the target gene is placed in a harmless virus)
Serum therapy is a treatment in which animals such as horses are injected with toxins or pathogens to make them produce antibodies, and then the serum(a fluid containing antibodies) is injected into a patient. It was established in the 1890s by Shibasaburo Kitasato and Emil von Behring.
Vaccination（Administering a vaccine to acquire immunity against a pathogen in advance）
Live vaccine（A weakened pathogen; likely to provide long-term immunity）
Inactivated vaccine（A pathogen whose pathogenicity has been eliminated; highly safe）
Toxoid（A vaccine that uses a detoxified toxin as an antigen）
mRNA vaccine（A new-generation vaccine that administers mRNA for making antigen proteins）
Serum therapy（A method of directly treating a patient by injecting serum containing antibodies from another animal）
Herd immunity（The effect of preventing the spread of infection when many people have immunity）
Further Study
mRNA vaccines are groundbreaking technology first put into practical use in the 2020s as a measure against COVID-19. Unlike conventional vaccines, mRNA for making the spike protein of the virus is enclosed in lipid nanoparticles(LNP) and administered. The mRNA is translated into antigen inside the body's own cells, and the immune system recognizes it. Their advantages include a short development period and flexible response to variants. Their developers, including Katalin Karikó, received the Nobel Prize in Physiology or Medicine in 2023.
The essential difference between vaccines and serum therapy: vaccines provide active immunity(the body makes its own antibodies・memory is formed・for prevention・long-lasting), while serum therapy provides passive immunity(antibodies are received from another individual・no memory is formed・for treatment・short-lasting). Herd immunity is the effect by which even unvaccinated people become less likely to become infected when the vaccination rate exceeds a certain level; for measles it is about 95%, while for COVID-19 it varies depending on pathogenicity.
- Vaccine=prevention by creating memory cells(active immunity)
- Serum therapy=injection of antibodies themselves(passive immunity)
- Three classical types=live vaccines・inactivated vaccines・toxoids
- mRNA vaccine=next-generation vaccine that makes antigens in the body's own cells
- Shibasaburo Kitasato・Emil von Behring=established serum therapy
- Herd immunity=infection control by increasing the vaccination rate
- Active immunity lasts a long time, while passive immunity lasts a short time
Points to Note
① Vaccines(prevention) and serum therapy(treatment) have opposite purposes. ② Active immunity(the body makes its own antibodies) and passive immunity(antibodies from another individual). Antibodies received from the mother through the placenta are also passive immunity. ③ Live vaccines may be dangerous when immunity is weakened. ④ mRNA vaccines administer mRNA, but the mRNA is broken down inside cells within several days and is not incorporated into human genes(DNA).
Practice
- What is the vaccine that administers nucleic acid encoding antigen proteins and was put into practical use for COVID-19 called?
- Who was the Japanese medical scientist who established serum therapy?
- Are vaccinations classified as active immunity or passive immunity?