Immunity (medicine)

Your body has a way to stay well.

It fights off bad things. It uses two parts to stay strong. One part is always there to help. It is your first line of defense.

The other part can learn. It learns to recognize specific germs. This helps your body remember them later. You can get this help from a shot. This is called a vaccine. It helps you stay healthy and strong.

Your body has a way to stay well. This is called immunity.

Immunity helps your body fight off germs. It has two main parts. The first part is innate immunity. This part is always there. It acts as your first line of defense. It works to stop germs from causing an infection.

The second part is adaptive immunity. This part is more advanced. It uses special cells called lymphocytes. These cells can learn to recognize specific germs. They also create a memory. This memory helps your body fight the same germ later.

You can get adaptive immunity in two ways. You can get it naturally from an infection. You can also get it through a vaccine. A vaccine is a way to make your body strong without getting sick.

There is also passive immunity. This is when you get ready-made help. A baby gets this from its mother. This happens through the placenta.

It can also happen through breast milk. This help is short-lived. It does not create a memory in your body.

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.

Immunity is the biological state of being resistant to a noxious agent or process. This resistance is especially important against a pathogen, which is an infectious agent that causes disease. In a healthy biological environment, the body maintains a balance between "self" and "non-self." The system aims to spare the body's own tissues while eliminating foreign substances through inflammatory and immunological responses. When the body fails to eliminate foreign invaders, or when it accidentally attacks its own tissues, disease can arise.

The immune system operates through two primary components: innate immunity and adaptive immunity. Innate immunity, also called native immunity, serves as the first line of defense. It is a semi-specific and widely distributed response that helps maintain homeostasis. Unlike the adaptive system, innate immunity does not change based on prior infections. Instead, it relies on genetically encoded recognition of specific patterns to identify threats. It includes processes such as inflammatory responses and phagocytosis, where cells engulf foreign particles.

Adaptive immunity is the more advanced, active component of the host response. This system is mediated by antigen-specific lymphocytes, which are specialized cells. Adaptive immunity is highly specific to particular pathogens and possesses the unique ability to develop immunological memory. This memory allows the body to recognize and respond more effectively to the same pathogen if it returns. The adaptive system is divided into two functional parts: humoral immunity and cell-mediated immunity.

There are several ways an organism can acquire these different types of protection. Active immunity occurs when the body is exposed to a pathogen, triggering the production of its own antibodies. This can happen naturally through infection or artificially through vaccination. Passive immunity, however, involves the transfer of ready-made antibodies or activated T-cells from an immune host. While passive immunity provides immediate protection, it is short-lived because the recipient does not develop immunological memory. This often requires booster doses for continued protection.

Passive immunity can be acquired through natural or artificial means. Naturally, a fetus acquires maternal passive immunity when antibodies are passed through the placenta. This occurs around the third month of gestation via an FcRn receptor on placental cells. IgG is the only antibody isotype capable of passing through the placenta. Additionally, mothers pass IgA antibodies through breast milk, such as colostrum, to protect a nursing infant's gut. Artificially, passive immunization uses human or animal blood plasma, pooled human immunoglobulin, or monoclonal antibodies. This is often used when there is a high risk of infection and no time for the body to react.

Human understanding of immunity has evolved significantly over thousands of years. Prehistoric views often attributed disease to supernatural forces or divine punishment. In Classical Greece, Hippocrates suggested that illness resulted from an imbalance of the four humors: blood, phlegm, yellow bile, and black bile. In 430 BC, the Athenian Thucydides observed that survivors of a plague were free from apprehension because they were not attacked a second time. In the 9th century, the Islamic physician Al-Razi provided the first clinical description of how exposure to smallpox and measles confers lasting immunity.

Modern immunology grew from the rejection of the miasma theory, which claimed "bad air" caused diseases like cholera. The 19th century saw the rise of germ theory and major scientific breakthroughs. In 1882, Ilya Mechnikov revealed the process of phagocytosis. Louis Pasteur's work with germ theory helped explain how bacteria cause disease and how bodies resist them. In 1798, Edward Jenner developed the smallpox vaccine by using the cowpox virus, a method known as vaccination. By 1890, the discovery of antitoxins for diphtheria and tetanus by Behring and Kitasato marked a major success for therapeutic immunology.