How Your Immune System Functions

What is the immune system?
Outside of your body, foreign invaders are waiting for a chance to spread. Bacteria, viruses, parasites, and fungi can all grow inside your body-often at your expense. Your immune system keeps them away from your healthy cells and protects you from infection. It tries to keep these invaders out. When it fails to do so, your immune system attacks the harmful pathogens that spread the disease. To do this, your body uses a wide variety of cells and a network of organs, all communicating to block the threat.

Ways to get infected with germs
In order to use your healthy cells, the germs need to find a way inside your body. There are only a few ways in. Sometimes they enter your skin from wounds or insect bites. Sometimes they come from the food you eat or drink and can cause food poisoning. Sometimes pathogens get into your eyes, ears, nose, or mouth when you swim. Sometimes you breathe them into your lungs. Sometimes you come in contact with germs and then rub your eyes, nose, or food. You can get germs in all these ways.

How Your Skin Protects You
Your skin is like a resilient shield around your entire body. It’s your first line of defense against bacterial invasion. But your skin shield can be broken, whether it’s by a paper cut or a mosquito bite. Keep your wounds clean, dry, and bandaged to help prevent skin infections.

Flushing Bacteria
Your body produces a variety of fluids that flush out bacteria. Think of the tears in your eyes, the mucus in your nose, and the sweat on your skin. All of these keep the bacteria out and away from your body. And they all produce a special antibody, IgA, to prevent infection.

Lymph and Lymph Nodes
Lymph is a clear fluid that washes away your cells. Lymph contains T-cells, which both direct your immune response and attack infection and cancer cells. Lymph flows through your lymph vessels and blood vessels. Bean-shaped lymph nodes collect in your armpits, groin, and around your neck. The lymph nodes are where T cells and other white blood cells are concentrated and where foreign cells such as microbes, dead cells, and cancer cells are removed from the bloodstream and destroyed.

What is an antigen?
An antigen can be anything that triggers an immune response. This includes viruses and bacteria, but also foreign tissues (such as organ transplants). Your immune system can make mistakes, such as mistaking harmless plant spores for pathogens, or even mistaking some of your healthy tissue for invaders. When this happens, it can lead to an autoimmune disease, such as type 1 diabetes or lupus.

Immune Types.” Congenital” and “Acquired”
Your innate immune system is your first line of defense against infection and is made up of parts of your immune system that respond to infection immediately or within a few hours. It is made up of the parts of your immune system that can respond to an infection immediately or within a few hours. The innate immune system includes your skin and other physical barriers. It also includes a number of cells that activate your immune response so that invading germs can be attacked and destroyed.

When your body successfully fights off an infection, you gain immunity to that infection. And when you receive a vaccine or antibody serum, you may gain immunity. In acquired immunity, some of your immune cells remember the infection or vaccine, so if the invader reappears, you’re ready to stop it. Immunity may last a few months or a lifetime, depending on the disease. The strength of the immunity depends on the antigen, its concentration, and the way it enters the body.

What is bone marrow?
Your bones would be empty without bone marrow, which is the jelly-like tissue inside the bone. Bone marrow is the source of most blood cells. Blood cells begin in your bone marrow as stem cells before they mature and specialize. This includes your white blood cells, which are key to immunity.

Phagocytosis of phagocytes
When your immune system senses an intruder, it sends out phagocytes to engulf it. A phagocyte is a type of white blood cell that eats invading germs. Phagocytes include the largest white blood cells (monocytes) and the most common white blood cells (neutrophils).

Natural Killer Cells (NK Cells)
Natural killer cells (NK cells) are a type of lymphocyte that can destroy antigens and also kill other foreign cells it recognizes. But unlike other lymphocytes, NK cells do not need to be told what to attack. This helps them to fight a wide variety of foreign cells.

What are basophils and mast cells?
When you have an allergy, basophils and mast cells are responsible for your symptoms. These cells are also effective against parasites. Parasites are usually much larger than bacteria and viruses. So these more general immune cells are more effective against them.

Lymphocytes
Lymphocytes are the white blood cells that pose a deadly threat to infection. Lymphocytes are vital to your immune system and make up about 20 to 40 percent of your white blood cell supply. They can bind to billions of foreign substances and can clone themselves, and once cloned, make more disease-fighting copies. Some of these cells can remember past infections and can multiply rapidly when an infection occurs again. Some lymphocytes have been genetically engineered to fight cancer.

Too few or too many lymphocytes can cause problems. The normal count for adults is 1,000 to 4,800 lymphocytes per microliter of blood. In children, the normal count is between 3,000 and 9,500 lymphocytes per microliter of blood.

Lymphocytopenia. This disease is caused by a lack of lymphocytes in the blood. It can be mild or severe, and fever is the most common symptom.
Lymphocytosis: Shortly after you have fought off an infection, you may have a large number of lymphocytes in your blood, which are harmless. However, lymphocytosis can also be caused by a number of conditions, some of which are fatal. They include
Leukemia
Hepatitis A, B, and C
HIV/AIDS
Hypothyroidism
Tuberculosis
Pertussis

What is an antibody?
Antibodies do many important tasks. Which tasks? It depends on their specialization. They can kill bacteria or help other cells digest microorganisms. Some antibodies mark invading cells so that other immune cells can attack. These antibodies are sometimes referred to as Ig (immunoglobulin). The three main types of antibodies are IgA, IgM, and IgG.

T Cell Types. Helpers and Killers
T cells are the main type of lymphocyte. t cells can either coordinate their destruction or attack them directly. there are two main types of t cells.

Helper T cells. These immune cells live up to their name. They can command phagocytes to engulf microorganisms. They can drive the production of antibodies. And they can trigger more helper T-cells.
Killer T cells (CTLs). These blood cells can find infected cells and kill them, including some cancer cells.

What is the function of the thymus gland?
Your thymus gland is located behind the chest plate in front of your chest, and T-cells thrive in this lymphatic organ, where they develop and multiply. This is where T-cells learn the difference between your healthy cells and foreign cells, and where they learn to distinguish between antigens.

Spleen, tonsils, appendix
The spleen is an organ located in the upper left side of the abdomen that filters foreign cells and has special compartments for immune cells to accumulate and work. It filters foreign cells and has special compartments for immune cells to accumulate and work. Like the lymph nodes, the spleen is the battleground between immune cells and antigens.

Your tonsils and appendix are some of the many areas in your body where lymphatic tissue comes together. Other areas include the lining of your respiratory and digestive tracts. These are the gateways to your body, so these organs act as gatekeepers, patrolling for infectious pathogens.

What are memory cells?
During and after infection, your white blood cells will surge, but most of them will not stay in your body for long. After a while, most cells will destroy themselves. However, a few cells will survive longer. These remaining cells are called memory cells. They provide the blueprint for your body’s immune response if the infection occurs again.

The Complement System. How it works
The complement system is a network of about 30 proteins. They complement the work of antibodies by responding to and destroying bacteria and antigens that bind to them. They do this through a complex series of interactions called the complement cascade. This cascade forms a tight protein cylinder that penetrates the cell wall, causing it to swell and burst. The complement system also contributes to the redness, pain, and swelling of inflammation.

What is a cytokine?
Cytokine proteins are chemical messengers. They have many functions. Some cytokines can turn other immune cells on and off. Other cytokines gather at the site of infection or injury and send chemical signals to attract other immune cells. Cytokines usually cause inflammation.

Abnormal Immune Response
Your immune system is complex and relies on many chemical reactions. They are not always. Sometimes you react to a harmless foreign substance such as ragweed pollen, which is an allergic reaction. Sometimes an error in the immune system can lead to an immune disorder, which can be of two types. An overreaction of the immune system that damages your body is called an autoimmune disorder. A weakened immune response is known as an immunodeficiency disorder.

Autoimmune disorders. Autoimmune diseases can be caused by a mix of genetics and environment. These diseases include Crohn’s disease, multiple sclerosis, and type 1 diabetes.
Immunodeficiency diseases. These are usually caused by chronic diseases, such as cancer or drug use, and are sometimes inherited. These diseases weaken the body’s immune system, making it less able to fight bacteria, viruses, cancer cells, and other harmful cells. Leukemia, HIV/AIDS, and other chronic diseases, including diabetes, can cause these diseases.