Immunity

Defenses Against Disease

Lymph nodes makes lymphocytes.

Cilia in respiratory tract sweep away debris.

Skin acts as a barrier.

Stomach acid kills bacteria.

Spleen filters out bacteria.

White blood cells engulf microorganisms.

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.