The Immune System

• Lymphatic system• Defence system

• Immune system disorders

• Inside your body there is an amazing protection mechanism called the immune system. It is designed to defend you against millions of bacteria, microbes, viruses, toxins and parasites (pathogens) that would love to invade your body

THE LYMPHATIC SYSTEM

• A network of vessels and nodes throughout the body

• Lymph is a pale, yellow interstitial fluid (similar to blood plasma)

• Lymph serves to maintain fluid balance in the body

• Lymph nodes contain lymphocytes and macrophages (phagocytic monocytes) which serve to trap & destroy bacteria

LYMPH NODES

• Viral and bacterial infections are by far the most common causes of illness for most people. They cause things like colds, influenza, measles, mumps, malaria, AIDS and so on. The job of your immune system is to protect your body from these infections. The immune system protects you in three different ways:

1. It creates a barrier that prevents bacteria and viruses from entering your body. (eg – skin)

2. If a bacteria or virus does get into the body, the immune system tries to detect and eliminate it before it can make itself at home and reproduce. (eg – phagocytic white blood cells)

3. If the virus or bacteria is able to reproduce and start causing problems, your immune system is in charge of eliminating it. (eg – B and T cells)

The Immune System is the Third Line of Defense Against Infection

Figure 22.10

Nonspecific Defenses (FIRST LINE - Physical Barriers)

Nonspecific Defenses(SECOND LINE - Phagocytes)

Figure 22.10

Figure 22.10

Nonspecific Defenses(SECOND LINE - Immunological

Surveillance)Natural killer T cells (cytotoxic T cells) destroy body cells that have become

cancerous or infected by viruses

Figure 22.10

Nonspecific Defenses(SECOND LINE –

Complement System)

Specific Defences(Antibody-Mediated Immunity)

• Antibodies are proteins that recognize foreign substances (antigens) and try to neutralize or destroy them.

• Antibodies are produced by LYMPHOCYTES

• All white blood cells are known officially as Leukocytes.

• White blood cells are not like normal cells in the body - they actually act like independent, living single-cell organisms able to move and capture things on their own.

•White blood cells behave very much like amoeba in their movements and are able to engulf other cells and bacteria.

• Many white blood cells cannot divide and reproduce on their own, but instead have a factory somewhere in the body that produces them. That factory is the bone marrow.

• Antibodies are produced by white blood cells.

• They are Y-shaped proteins that each respond to a specific antigen (bacteria, virus or toxin).

• Each antibody has a special section (at the tips of the two branches of the Y) that is sensitive to a specific antigen and binds to it in some way.

• When an antibody binds to the outer coat of a virus particle or the cell wall of a bacterium it can stop their movement through cell walls. Or a large number of antibodies can bind to an invader and signal to the complement system that the invader needs to be removed.

The immune system response

• Antigen triggers an immune response • Activates T cells and B cells

– T cells are activated after phagocytes exposed to antigen

• T cells attack the antigen and stimulate B cells• Activated B cells mature and produce antibody• Antibody attacks antigen

Figure 22.15

An Overview of the Immune Response

Major types of T cells

• Cytotoxic (Killer) T cells – attack foreign cells – pucture a hole in cell membrane

• Helper T cells – activate other T cells and B cells• Suppressor T cells – inhibit the activation of T and

B cells – make sure normal tissue isn’t destroyed• Memory T cells – remain in bloodstream and can

act quickly if antigen comes into blood again

Types of Immunity

Figure 22.14

IMMUNE SYSTEM DISORDERS

ALLERGIES

• An allergy is an exaggerated response of the immune system to a harmless material (eg – pollen, pet dander, grass, peanuts, etc)

ALLERGIES

2 types of allergic reactions:

• Immediate (or acute)

- occurs within seconds of exposure – disappears within 30 minutes

(eg) pets, nuts, pollen

• Delayed

- reaction is slower and lasts longer

- T-cells are sensitized by previous contact

(eg) cosmetics, jewellery

What happens during an immediate allergic reaction?

• Specialized antibodies trigger certain cells to release histamines

• Histamines are chemicals that increase the permeability of blood vessels

• Therefore, blood (mostly plasma with some WBCs) leaks out of the vessels and into the tissues – causing them to become red and swollen

• Symptoms: itchy, puffy eyes, runny nose, constriction of airways (asthma, or anaphylaxis)

What is anaphylaxis?

• Anaphylaxis is a severe allergic reaction to a specific allergen – eg peanuts, bee stings, etc.

• Airways can close almost immediately – which can be fatal

• An injection of adrenaline (Epi-pen) is given

COMMON ALLERGENS

AUTOIMMUNE DISORDERS

• Your body identifies your own cells as “self” cells

• Sometimes, T cells or antibodies make mistakes and attack your own cells, mistaking them for “non-self” cells

• An autoimmune disorder is the result

• EXAMPLES: rheumatoid arthritis, Type I diabetes

RHEUMATOID ARTHRITIS

• A chronic autoimmune disorder

• Characterized by inflammation of the joints

• Most common in people 25-50 years

• Immune system attacks bone, cartilage, ligaments