Immunity

Defenses Against Disease Lymph nodes makes lymphocytes. White blood cells engulf microorganisms. Cilia in respiratory tract sweep away debris. Spleen filters out bacteria. Stomach acid kills bacteria. Skin acts as a barrier.

Immunity The ability of the body to resist disease. First studied by Edward Jenner in 1776. He found that he could use fluid from a cowpox sore to vaccinate against smallpox (often fatal).

How Immunity Works The body is able to tell the difference between “self “(its own cells and molecules) and “ nonself “ (foreign cells and molecules).

How Immunity Works The reaction of the body to “nonself” cells is called the immune response. This involves destroying or neutralizing foreign cells or molecules with white blood cells and lymphatic tissue.

The Immune Response Antigens cause the immune response to happen. Most antigens are proteins, but some are carbohydrates and nucleic acids. Most microorganisms and toxins contain antigens.

The Immune Response Recognition and destruction of foreign antigens is the job of the lymphocytes. Lymphocytes are made in the bone marrow of the embryo and are stored in lymphoid tissue.

Two Types of Lymphocytes (B & T) Each lymphocyte has receptors for only one antigen. When the receptors recognize the antigen, the lymphocytes become activated.

Activation of B Lymphocytes (BLs) When BLs are activated, they enlarge and divide repeatedly to form two different cell types: 1. Plasma Cells 2. Memory Cells

1. Plasma Cells Plasma cells secrete antibodies, which are proteins that react specifically with antigens and inactivate them. Antibodies have active sites that fit a compatible site on a certain antigen.

Antigen-Antibody Reactions There are many different types of antibodies and they inactivate antigens in five different ways. antigens antibodies

Antigen-Antibody Reactions 1. Agglutination: Antigens are clumped together and thus inactivated. 2. Precipitation: Antibodies form a complex with the antigens, and the complex settles out.

Antigen-Antibody Reactions 3. Neutralization: Antibodies combine with antigens, inactivating the toxic site of the antigen molecule.

Antigen-Antibody Reactions 4. Lysis: Antibodies cause the cell membranes of the antigenic microorganisms to burst.

Antigen-Antibody Reactions 5. Complement System: The complement system is a group of enzymes in the plasma. The antigen-antibody complex activates these enzymes, which attack the antigenic material.

2. Memory Cells The memory cells stay in the lymphoid tissue. If the same antigen enters the body, the memory cells will immediately produce antibodies against it.

Activation of T Lymphocytes (TLs) When TLs contact an antigen, they divide rapidly and make more TLS.Some stay in the lymphoid tissue as memory cells. Other TLs pass into the circulatory system and body tissues, where they combine with the antigens and destroy them.

How Lymphocytes Make Antibodies Click here for animation.

Types of Immunity Three main types of immunity: 1. Inborn Immunity 2. Acquired Immunity 3. Passive Immunity

1. Inborn Immunity Does not involve antibodies. Present in all humans from birth. Prevents humans from becoming infected with certain types of bacteria and viruses. Ex. Feline leukemia affects cats not humans.

2. Acquired Immunity Two ways to get it: 1. Contracting a disease-Ex. Chicken pox. Memory cells will,stay in the body and produce antibodies. 2. Vaccination-Vaccine serves to stimulate the production of specific antibodies to certain antigens.

3. Passive Immunity Does not last long (about one month). Body destroys the “borrowed” antibodies. Fast acting. Found in babies who get antibodies via mother’s milk. Helps protect child for a few months.