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.