Immune System

The immune system, which is made up of special cells, proteins, tissues, and organs, defends people against germs and microorganisms every day. In most cases, the immune system does a great job of keeping people healthy and preventing infections. But sometimes problems with the immune system can lead to illness and infection.

The immune system is the body's defense against infectious organisms (pathogens) and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade body systems and cause disease.

Here is an example of how a particular kind of pathogen, a virus, could infect one of your cells and begin to spread.

Antibodies and Antigens

The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The cells involved are white blood cells, or leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms, called pathogens.

T-cells help coordinate the attack on pathogens and help identify and remove infected cells. B-cells produce defensive proteins called antibodies that lock on to specific pathogens, disabling them and allowing other white blood cells to engulf and destroy them, a process known as phagocytosis.

This video shows how antibodies attach to the antigens of a pathogen. Antigens are protein structures on the invading microbe that allow it to enter a cell. Your immune system targets these specifically-shaped antigens with antibodies that have a shape that fits perfectly onto the antigen. The antibody (from your body) fits only with one type of antigen (on the pathogen). Think of the antibodies as hand-cuffs, disabling the pathogen.

The T-cells B-cells that worked together to produce the successful antibody reproduce themselves and remain in your lymph nodes and blood stream, effectively "remembering" how to fight off that pathogen. At that point, you have become immune to the pathogen.

Immunity is fantastic. Your body wipes out a specific pathogen before it has the chance to make you sick again. The only downside is that you had to get sick the first time. But guess what: science and medicine have discovered how to make you immune to a pathogen WITHOUT getting sick from it. Vaccines! This is especially helpful for more severe diseases like the measles, HPV, tetanus and polio.

Vaccines

Vaccines are designed to prepare your immune system so that when a particular pathogen enters your body in the future, the correct B-cells will already be plentiful and ready to fight off infection by producing antibodies extremely rapidly.

When biologists identify a pathogen, they can weaken it by removing or destroying the genetic material inside. The outside shape (antigens) of the pathogen is still the same, so when it is injected into an individual, the pathogen will not make them sick but its antigens will be able to be recognized by their immune system. The B-cells will learn about the pathogen's shape and produce antibodies that will be present if and when the person ever encounters the real pathogen in the future.

For example: here is how the HPV vaccine works:

Allergies

Allergies are a disorder of the immune system during which an overreaction to a harmless antigen creates uncomfortable symptoms of inflammation, sometimes in life-threatening amounts.

As part on an immune response to foreign antigens, histamine is produced by certain white blood cells. Histamine increases the ability of capillaries to allow diffusion of fluids, white blood cells, and various proteins. This allows for an increased ability to engage with potentially harmful foreign invaders. The increased diffusion of fluids to an area creates swelling and is called inflammation.

During a severe allergic reaction, too much histamine is released in response to a harmless antigen such as peanut oil or pollen. The large amount of swelling can restrict airways, and the dramatic loss of fluid from blood vessels could cause a dangerous drop in blood pressure. Anti-histamine drugs counter the effects of histamine. Adrenaline (aka epinephrine) is a hormone that can work to raise your blood pressure, and can be injected in cases of extreme allergic reactions (epi-pen).

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