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Your immune system is a complex network of cells, tissues, and organs. Together they help the body fight infections and other diseases. When germs such as bacteria or viruses invade your body, they attack and multiply. This is called an infection.

The immune system is the body's defense against infections. The immune (ih-MYOON) system attacks germs and helps keep us healthy.

Many cells and organs work together to protect the body. White blood cells, also called leukocytes (LOO-kuh-sytes), play an important role in the immune system.

Some types of white blood cells, called phagocytes (FAH-guh-sytes), chew up invading organisms. Others, called lymphocytes (LIM-fuh-sytes), help the body remember the invaders and destroy them.

One type of phagocyte is the neutrophil (NOO-truh-fil), which fights bacteria. When someone might have bacterial infection, doctors can order a blood test to see if it caused the body to have lots of neutrophils. Other types of phagocytes do their own jobs to make sure that the body responds to invaders.

The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes start out in the bone marrow and either stay there and mature into B cells, or go to the thymus gland to mature into T cells. B lymphocytes are like the body's military intelligence system — they find their targets and send defenses to lock onto them. T cells are like the soldiers — they destroy the invaders that the intelligence system finds.

When the body senses foreign substances (called antigens), the immune system works to recognize the antigens and get rid of them.

B lymphocytes are triggered to make antibodies (also called immunoglobulins). These proteins lock onto specific antigens. After they're made, antibodies usually stay in our bodies in case we have to fight the same germ again. That's why someone who gets sick with a disease, like chickenpox, usually won't get sick from it again.



This is also how immunizations (vaccines) prevent some diseases. An immunization introduces the body to an antigen in a way that doesn't make someone sick. But it does let the body make antibodies that will protect the person from future attack by the germ.

Although antibodies can recognize an antigen and lock onto it, they can't destroy it without help. That's the job of the T cells. They destroy antigens tagged by antibodies or cells that are infected or somehow changed. (Some T cells are actually called "killer cells.") T cells also help signal other cells (like phagocytes) to do their jobs.

Antibodies also can:

neutralize toxins (poisonous or damaging substances) produced by different organisms
activate a group of proteins called complement that are part of the immune system. Complement helps kill bacteria, viruses, or infected cells.
These specialized cells and parts of the immune system offer the body protection against disease. This protection is called immunity.

Humans have three types of immunity — innate, adaptive, and passive:

Innate immunity: Everyone is born with innate (or natural) immunity, a type of general protection. For example, the skin acts as a barrier to block germs from entering the body. And the immune system recognizes when certain invaders are foreign and could be dangerous.
Adaptive immunity: Adaptive (or active) immunity develops throughout our lives. We develop adaptive immunity when we're exposed to diseases or when we're immunized against them with vaccines.
Passive immunity: Passive immunity is "borrowed" from another source and it lasts for a short time. For example, antibodies in a mother's breast milk give a baby temporary immunity to diseases the mother has been exposed to.
The immune system takes a while to develop and needs help from vaccines. By getting all your child's recommended vaccines on time, you can help keep your child as healthy as possible.

5 Ways to Boost Your Immune System
Maintain a healthy diet
As with most things in your body, a healthy diet is key to a strong immune system. This means making sure you eat plenty of vegetables, fruits, legumes, whole grains, lean protein and healthy fats.

In addition to providing your immune system the energy it needs, a healthy diet can help ensure you're getting sufficient amounts of the micronutrients that play a role in maintaining your immune system, including:

Vitamin B6, found in chicken, salmon, tuna, bananas, green vegetables and potatoes (with the skin)
Vitamin C, found in citrus fruit, including oranges and strawberries, as well as tomatoes, broccoli and spinach
Vitamin E, found in almonds, sunflower and safflower oil, sunflower seeds, peanut butter and spinach


Since experts believe that your body absorbs vitamins more efficiently from dietary sources, rather than supplements, the best way to support your immune system is to eat a well-balanced diet.

Exercise regularly
Physical activity isn't just for building muscles and helping yourself de-stress — it's also an important part of being healthy and supporting a healthy immune system.

One way exercise may improve immune function is by boosting your overall circulation, making it easier for immune cells and other infection-fighting molecules to travel more easily throughout your body.

In fact, studies have shown that engaging in as little as 30 minutes of moderate-to-vigorous exercise every day helps stimulate your immune system. This means it's important to focus on staying active and getting regular exercise.

Hydrate, hydrate, hydrate
Water plays many important roles in your body, including supporting your immune system. A fluid in your circulatory system called lymph, which carries important infection-fighting immune cells around your body, is largely made up of water. Being dehydrated slows down the movement of lymph, sometimes leading to an impaired immune system.

Even if you're not exercising or sweating, you're constantly losing water through your breath, as well as through your urine and bowel movements. To help support your immune system, be sure you're replacing the water you lose with water you can use — which starts with knowing how much water you really need.

Get plenty of sleep
Sleep certainly doesn't feel like an active process, but there are plenty of important activities happening in your body when you're not awake — even if you don't realize it. For instance, important infection-fighting molecules are created while you sleep.

Studies have shown that people who don't get enough quality sleep are more prone to getting sick after exposure to viruses, such as those that cause the common cold. To give your immune system the best chance to fight off infection and illness, it's important to know how much sleep you should be getting every night, as well as the steps to take if your sleep is suffering.

Minimize stress
Whether it comes on quick or builds over time, it's important to understand how stress affects your health — including the impact it has on your immune system. During a period of stress, particularly chronic stress that's frequent and long-lasting, your body responds by initiating a stress response. This stress response, in turn, suppresses your immune system — increasing your chance of infection or illness.

Stress is different for everyone, and how we relieve it is, too. Given the effect it can have on your health, it's important to know how to identify stress. And, whether it's deep breathing, mediation, prayer or exercise, you should also get familiar with the activities that help you reduce stress.

One last word on supplements
There's no shortage of supplements claiming they can stimulate your immune system — but be wary of these promises.

First thing's first, there's no evidence that supplements actually help improve your immune system or your chances of fighting off an infection or illness. In addition, unlike medications, supplements aren't regulated or approved by the FDA. For instance, if you think a megadose of vitamin C can help you keep from getting sick, think again.

If you're looking for ways to help boost your immune system, consider keeping up with the lifestyle habits above, rather than relying on claims on a label.