The Immune System

By: Lauren Ashley

Skin and Mucous Membrane

The first line of defense for the immune system are the skin and mucous membranes. Skin acts as a physical barrier, blocking pathogens from entering. Mucus within the nasal cavity blocks some of the pathogens from entering the body. Cilia also aids in protecting the immune system by acting as a barrier as well. There is also mucus lining the bronchial tubes, which like other mucus, blocks pathogens.

White Blood Cells

Neutrophil: Most abundant phagocyte, it circulates blood vessels and squeezes through the capillary walls to the infection sight and attacks pathogens.

Macrophage: Engulfs pathogens and cellular debris. Some are stationed in body tissues and other seek out pathogens in the body.

Natural Killer Cells: Large white blood cells that attack pathogen-infected cells.

Fevers and Proteins

When the body is fighting pathogens, the body temperature rises, letting you know that your body is responding and fighting off an infection. It also slows down bacteria growth and helps white blood cells attack pathogens. However, if the body gets too hot, it can destroy the important cellular proteins in the body. It's dangerous to have a body temperature over 103 degrees, and if you’re over 105 degrees you could easily die.


Antigens join with antibodies and cause lymphocytes to react. When lymphocytes recognize an antigen, they bind to the antigen to start a specific attack, called an immune response.


Lymphocytes have a unique receptor proteins all over the surface of its cell membrane. The receptor proteins recognize and bind to antigens to match their shape. Each kind of lymphocyte carries unique receptors, and when a specific pathogen enters the body, the lymphocytes that match the antigen of the pathogens respond.

B Cells vs. T Cells

B cells: Made in the bone marrow and they stay there until they are developed. They attack pathogens outside of the cells by dividing into plasma cells, as well as memory cells, which help remember the infection if it tries to attack again.

T cells: Made in bone marrow, but travel to the thymus to finish developing. They attack pathogens inside of the cell by recognizing and destroy cells that have been infected by a pathogen. Some of them also help shut down the immune response after the body has been cleared from the pathogen.

Immunity and Vaccines

Vaccines trick your body into thinking it is being infected, so your immunes cells (T cells and B cells) recognize the viral pathogens and build an immune defense to them. Since the virus is viable it won't infect your cells or replicate and make you sick. Vaccines cause your cells to remember the infection and build up from it. Next time you get that infection, your body will be ready to send a strong force of white blood cells right away and get rid of it. That way, it builds up an immunity to that disease. Vaccines are pretty much a practice drill, so your body can practice fighting a disease and prevent it from happening.

Passive vs. Active Immunities

Passive Immunity: In passive immunity, a person has antibodies passed down to them naturally, from their mother, or through human intervention. The antibodies given are already working and protect the recipient from illness.

Active Immunity: In active immunity, you build up immunities and antibodies to a pathogen by direct exposure to it. Your body itself is currently in the process of building up antibodies to pathogens to protect you. Your body memorizes the antigen, then it creates the antibodies, so you have a lower chance of getting it again. There is also another type of active immunity, which is when you are given a vaccine to help your body form antigens to the disease you are getting vaccinated for.

Allergies, Asthma, and Autoimmune Diseases

Allergy: They are physical responses to an antigen. Antigens that can trigger common allergic reactions include things like pollen, animal dander, dust mites, food, etc.

Asthma- They are allergies that can trigger respiratory disorder that causes the airways of the lungs to narrow. Asthma attacks can be caused by cigarette smoke, allergens, etc.

Autoimmune diseases: They are diseases in which the immune system attacks the organism's own cells. Lymphocytes that recognize and react to the body’s own cells are usually eliminated during development before they become functional. They also prevent an attack directed at the body’s own tissues.


AIDS is caused by an infection with a virus called human immunodeficiency virus (HIV). This virus is passed from one person to another through blood-to-blood or sexual contact. In addition, infected pregnant women can pass HIV to their babies during pregnancy or delivery, as well as through breast feeding. People with HIV have what is called HIV infection, and some of these people will develop AIDS as a result of their HIV infection.

The Three Phases of Infection (HIV)

Phase I: Called the "Asymptomatic stage." There are few or no symptoms, and the amount of virus increases due to replication. The immunes system, begins to attack, and plasma cells make antibodies to fight the virus. It usually takes several weeks for the amount of anti-HIV antibodies to become large enough to result in a positive HIV test.

Phase II: Phase II is the beginning or worsening of symptoms that mark the start of the second phase of HIV infection. B cells continue to make antibodies against HIV, but the number of T cells drops steadily as the virus continues to get stronger. The immune system fails, and lymph glands become swollen as a result. Side affects like fatigue, weight loss, fever, diarrhea develop or worsen. Some infected people may notice mental changes as well, like forgetfulness.

Phase III: The number of helper T cells drops so low they can’t stimulate B cells and cytotoxic T cells start to fight invaders. The amount of anti-HIV antibodies falls, and HIV rises dramatically. AIDS is diagnosed when the helper T cell count drops to 200 cells per milliliter of blood or lower. This is the stage of infection that occurs when your immune system is badly damaged and you become vulnerable to opportunistic infections. Without treatment, people who are diagnosed with AIDS typically survive about 3 years. Once someone has a dangerous opportunistic infection, life-expectancy falls to about 1 year.

Evolution of HIV

It is hard to develop a vaccine for HIV, because there is a ridiculous amount of strands to treat, and it keeps evolving. You could find a vaccine for one strand, but it would only treat the one specific strand that is usually unique to that one infected person. It is pretty much impossible to treat, but there have been some vaccines that are effective in slowing down the spread of the HIV virus.

Break-down of the Immune System (Vocab)

Bone Marrow: Makes billions of new lymphocytes needed by the body everyday.

Thymus: A gland located above the heart that helps produce a special kind of lymphocyte.

Lymphnodes: They are located throughout the body and contain lymphocytes. They also collect pathogens from the lymph and expose them to lymphocytes.

Spleen: Stores healthy blood cells that breaks down aging red blood cells, and it also helps develop lympocytes and other types of white blood cells. Another important thing it does is collect pathogens from the blood and attack them.

adenoids/tonsils- masses of lymph tissue found in the throat and nose.

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Immune response - Animation