Immunity (medicine)

Immunity is the way your body stays safe from harmful things. It helps you resist pathogens, which are tiny germs that cause disease.

You can get this protection naturally or through immunization. When your body stays healthy, it means it can tell the difference between "self" and "non-self." The immune system works to spare your own cells while eliminating foreign ones. This creates a dynamic environment that keeps you well.

Your immune system has two main parts that work together. The first part is innate immunity, which is always present. It acts as your first line of defense to prevent infection. It uses patterns to recognize germs rather than learning from them. The second part is adaptive immunity, which is much more specific. It uses special cells called lymphocytes to find exact germs. These cells also create an immunological memory to remember past invaders.

People have wondered about disease for thousands of years. In ancient times, some thought sickness came from supernatural forces. The Greek doctor Hippocrates believed it came from an imbalance of humors. In 430 BC, the Athenian Thucydides noted that people who recovered from a plague did not get sick again. Much later, the physician Al-Razi wrote about smallpox and measles in the 9th century. He noted that being exposed to these diseases gave lasting immunity.

Many important discoveries helped us understand how immunity works today. In 1882, Ilya Mechnikov showed how cells perform phagocytosis. Louis Pasteur later developed the germ theory of disease. In 1798, Edward Jenner created the smallpox vaccine using cowpox. This was a much safer method than older ways of inoculation. By 1890, scientists Behring and Kitasato discovered antitoxins for diphtheria and tetanus. These were the first big successes for modern medicine.

There are different ways to gain protection. Active immunity happens when your own body makes antibodies after seeing a germ. This can happen through an infection or a vaccine. Passive immunity is different because it gives you ready-made help. A baby gets this naturally from its mother through the placenta. Mothers also pass antibodies through breast milk to protect infants. This help is short-lived because your body does not make its own memory.