THE IMMUNE SYSTEM

What happens when we get sick?

Why do we get better?

How does your body know when a substance is an invader?

Functions of the Immune System

• 1. Recognize self vs. non-self

• 2. Destroy non-self

Foreign Invaders

• Antigen:

– Any non-self substance capable of triggering an immune response

– An antigen can be a whole non-self cell, a bacterium, or a virus.

• Even allergens and cancerous cells

Foreign Invaders

• Antibody:

– Protein that recognize and bind to pathogens.

– Once the body has been exposed to a pathogen, the body creates memory B cells, reducing the chance of being infected again!

ANATOMY OF THE IMMUNE SYSTEM

• The immune system is localized in several parts of the body

– immune cells develop in the bone marrow and thymus

– immune responses occur in the secondary organs

ANATOMY OF THE IMMUNE SYSTEM:The immune system is localized in several parts of the body

– Spleen: filters and removes old and damaged red blood cells

• removes infectious agents and uses them to activate cells called lymphocytes

– Bone marrow: tissue insides bones that produces blood cells

• B cells and T cells are types of white blood cells

ANATOMY OF THE IMMUNE SYSTEM:The immune system is localized in several parts of the body

– Thymus: T cells mature here (learn their job)

– Lymph nodes: small organs that filter out dead cells, antigens, and other “stuff” to present to lymphocytes

ANATOMY OF THE IMMUNE SYSTEM:The immune system is localized in several parts of the body

– Lymphatic Vessels: collects fluid (lymph) “leaked” from blood into the tissues and returns it to circulation

– Tonsils: 3 pairs masses of lymphoid tissue- helps protect against bacteria around the throat

– Appendix: “safe house” for the beneficial bacteria living in the human gut

• Non-specific defense mechanisms:– The body’s attempt to destroy all types of foreign

invaders – General, not targeted to a specific pathogen (virus

or bacteria)

• Specific defense mechanisms:– Immune response specific for a pathogen

There are three lines of defense against infection

First Line of Defense:The outer layer of the body

• Goal:prevent organisms from gaining access to the body

• Details:

– Physical barriers: skin, hair

– Chemical barriers: sweat, tears, saliva, mucus, skin

• These contain enzymes that break down cell walls of many bacteria

Second line of defense: Cells and proteins in our blood stream

• Goal: recognize, neutralize and destroy invaders inside the body• Details: inflammation and fever (swelling, redness, warmth, pain)

– Increased blood flow brings cells to fight infection• Macrophage, phagocytes, and neutrophils

Third Line of Defense: The Immune Response

• Two types of cells are involved:

– B cells: provide immunity against antigens and pathogens in the body fluids by making antibodies• This is called humoral immunity• Vaccines cause B cells to produce antibodies

– T cells: provide defense against abnormal cells and pathogens inside living cells• This is called cell-mediated immunity

Putting it all Together• 1. Virus infects body

Putting it all Together2.Macrophage (WBC) eat virus and display viral antigen

Putting it all Together• 3. White blood cell activates Helper T cell

Putting it all Together• 4. Helper T Cells activate B cells and killer T cells

Putting it all Together• 5. Some B cells become memory cells for future

immune response, some become plasma cells

Putting it all Together• 6. Plasma cells make antibodies which bind to viral antigen

Putting it all Together• 7. Antibodies attach to the virus and infected body cells, signals for their destruction

– Antibodies protect against foreign invaders

Putting it all Together• 8. Killer T cells destroy infected body cells

• 1. Virus infects body, cells display viral antigens• 2. Macrophages engulf virus and display viral

antigen• 3. Macrophages activate helper T cells• 4. Helper T Cells activate cytotoxic T and B cells• 5. B cells form plasma cells

– Some B cells become memory cells for immune response later on

• 6. Plasma cells make antibodies which bind to viral antigen

• 7. Antibodies attach to the virus and infected body cells, signals for their destruction– Antibodies protect against foreign invaders

• 8. Cytotoxic T cells destroy infected body cells

HIV (Human Immunodeficiency Virus)

• Cause: – Human Immunodeficiency Virus

• Symptoms:– Fever, headache, tiredness, enlarged lymph nodes– AIDS (Acquired Immunodeficiency Syndrome)

• weight loss, fatigue, memory loss – Destroys Helper T cells (part of immune system)

• body cannot fight off illnesses caused by bacteria, other viruses, fungi, or parasites.

• Ultimately leads to death

HIV (continued)• Treatment:

– Reverse Transcriptase (RT) inhibitors & Protease Inhibitors- stops the virus from making copies of itself

• Transmission:– sexually (orally, vaginally)– Blood (needles, or through mucus membranes)– Breast milk mother to child– NOT from kissing, touching, insects bites

• Status:– No vaccine, several medicines to prevent spread in body– Worldwide: In 2004, 40 million people living with HIV/AIDS, 5

million newly infected, and 3.1 million deaths

• Prevention:– Abstinence, Safe sex (Condoms!), avoidance or risky behaviors

associated with sex and drug use