The Immune System

The Antigen Antibody Reaction

Antigen-Antibody reactions refer to the interaction between antigens and antibodies. These are reactions are studied under two different headings namely in vivo and in vitro reactions.

In vivo Ag-Ab reactions:

These reactions refer to the Ag-Ab reactions occurring inside the host. In the body, they form the basis of antibody mediated immunity in infectious diseases or of tissue injury in some types of hypersensitivity and autoimmune diseases. Functions of antibodies are also included under this category. They are

a. Agglutination

b. Neutralization

c. Opsonization (IgG1 and 3)

d. Complement fixation (IgM and IgG)

e. Induction of inflammation (IgE)

Specific and Nonspecific Immunity

Nonspecific immunity is when components eliminate pathogens before they can cause disease.

Specific immunity is when components adapt to new diseases (by creating memory cells) and their main role becomes to attack a certain kind of pathogen.

NONSPECIFIC DEFENSE MECHANISMS:

A). Skin and Mucus membranes
Skin is an impenetrable barrier to viruses and bacteria if it is not broken.
It is reinforced by chemical defenses. Oil and sweat give the skin a pH of 3-5.
Bacteria that live on the skin help by releasing acids and wastes to kill off unwanted microorganisms. Lysozyme is found in tears and saliva which can destroy the cell walls of most bacteria. Gastric juices kill off bacteria in food. Mucus captures bacteria in the nose and throat cavities of the body.

B). Phagocytes and Natural Killer Cells

Phagocyte are cells that eat other cells or objects found in the body.
Macrophages a type of phagocyte that eats bacteria, viruses, and the debris of damaged cells. They develop from a class of white blood cells called MONOCYTES. Neutrophils are another type of white blood cell capable of becoming phagocytotic.

Natural Killer Cells destroy the bodies own infected cells, especially those containing viruses. They may attack cells that might form tumors. They do not eat the cell but lyse it

C). Inflammatory Response

Damage to tissue by physical injury will trigger an inflammatory response.
Small blood vessels in the area will dilate and become leakier. This causes the redness and heat of the infected area. This enhances the migration of phagocytes into the area. Neutrophils arrive first, followed by monocytes that develop into macrophages. Clotting proteins seal off the infected area.
Injured cells release HISTAMINE which induces the dilation of the capillaries.
Sometimes white blood cells release chemicals called pyrogens. They act on the bodies thermostat and raise the temperature in an effort to kill the microorganism.

Antimicrobial Proteins

Interferons: Acts in warning other cells of a viral invasion. It is produced by infected cells.

Complement: Circulate in the body in an inactive form. They are activated by chemical markers, or the onset of the immune response.

SPECIFIC DEFENSE MECHANISMS:

Immune Response = a recognition system that distinguishes "self" form "non-self".
Antigen = Foreign substance.
Antibody = specific defensive proteins which help to counter antigens is various ways.
Immunity = protection afforded to an organism by previous exposure to an antigen.
Active Immunity = Immunity conferred by an encounter with the actual virus or bacterium. The body actually produces antibodies in its own defense.
Passive Immunity = Temporary acquired antibodies passed on to the organism. No antigen is passes on.

The Immune response is governed by 2 different parts of the immune system.
Humoral Immunity: results in the production of antibodies that circulate around the body in blood and lymph (humors).Defends against: free bacteria and viruses.
Cell-mediated Immunity: defense activities are carried out by specialized cells circulating around the body. Defends against: host cells infected with bacteria and viruses, fungi and protozoans, tissue transplants, own cancer cells.

Skin's function

Your body has a host of different defensive techniques to keep you protected from foreign invaders such as bacteria, viruses, and even household allergens. Whether it be the macrophages of your immune system or the earwax in your ear, the body is amazing at defending itself. One of the largest defense mechanisms that your body has is also the largest organ of your body: your skin.

The main way that your skin protects you against disease is through acting much as armor does to knight. The skin creates an impermeable layer that separates your body's internals from the disease causing bacteria and viruses outside of you. Of course, a break in the skin barrier can allow disease to make its way into the body, but as long as the skin is free of cuts or open sores, foreign invaders are unable to get in.

The skin also protects you from diseases by shedding on a regular basis. Although disease causing bacteria and viruses are unable to get through the skin to infect you without help from an opening or sore, they can attach themselves to the skin. Your skin is constantly making new cells and shedding old ones. When the dead skin cells are shed off your body to make room for the new cells, the bacteria and other disease causing agents fall of with the skin cells as well, removing them from the body.

Vaccination & Immunity

Relationship between vaccination and immunity

If you're immune to something, your system is resistant to it. However, if you're vaccinated, you're not immediately immune, and in fact, it may not help you at all. When you're vaccinated, you're simply given a shot.

What happens during an allergic response?

Allergic reactions are common. The immune response that causes an allergic reaction is similar to the response that causes hay fever. Most reactions happen soon after contact with an allergen.

Many allergic reactions are mild, while others can be severe and life-threatening. They can be confined to a small area of the body, or they may affect the entire body. The most severe form is called anaphylaxis or anaphylactic shock. Allergic reactions occur more often in people who have a family history of allergies.

Substances that don't bother most people (such as venom from bee stings and certain foods, medications, and pollens) can trigger allergic reactions in certain people.

Although first-time exposure may only produce a mild reaction, repeated exposures may lead to more serious reactions. Once a person has had an exposure or an allergic reaction (is sensitized), even a very limited exposure to a very small amount of allergen can trigger a severe reaction.

Most severe allergic reactions occur within seconds or minutes after exposure to the allergen. However, some reactions can occur after several hours, particularly if the allergen causes a reaction after it has been eaten. In very rare cases, reactions develop after 24 hours.

The immune system

Describe the function of the immune system.

-The purpose of the immune system is to keep infectious microorganisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious microorganisms that do invade the body.

Describe the actions of B cells and T cells in an immune response.

- T-cells are the ones that grab onto the antigens in your body (bacteria, viruses, etc). The T-cells then present them to the B-cells, which are the ones that actually make antibodies against the antigens. B-cells and their antibodies are called humoral immunity. T-cells and their effects on other cells are called cellular immunity.

Describe at least two immune disorders.

- Lupus. It is more common in women than in men. It is not believed to be contagious, and the exact cause of the disease has not been determined. Some research seems to show that lupus may be at least in part due to genetics, as people who have relatives who suffer from the disease have a higher risk of contracting lupus themselves. Some researchers believe there may be an environmental trigger that brings about the onset of lupus. Smoking and exposure to ultraviolent light are possibly linked to the disease.

Multiple sclerosis (MS) is an immune disorder that primarily affects the nervous system. It is considered a localized disorder, but because it attacks the nervous system, the symptoms can exhibit in many parts of the body. MS is a disease that causes the immune system to attack the protective coating of nerves. The severity of the disease varies greatly from one individual to another, but in very extreme cases, suffers may be unable to walk or speak. There is currently no cure for MS.