10.1 The Body’s Lines of Defence• David Vetter (1971-

1984)• Born with severe

combined immunodeficiency (SCID)

• SCID is an X-linked disorder, and David’s mother was a carrier

• Ten seconds after birth, David was placed in a plastic bubble

David Vetter

• David needed a germ-free environment, so he had to be inside his bubble for 12 years

• Doctors hoped to cure SCID using a bond marrow transplant

The Bone Marrow Transplant

• October 21, 1983, David received a bone marrow transplant from his sister, Katherine

• The marrow contained the Epstein-Barr virus that causes mononucleosis

Medical Ethics

• While knowing that David would have to live life in a bubble, doctors encouraged his mother to go through with the pregnancy. Some people have said that in this situation, it would have been better to terminate the pregnancy.

• What do you think?

What was gained?

• Doctors now know that SCID can be treated within three months of birth with bone marrow screened for pathogens

The Three Lines of Defense

• The first and second lines of defense of the human body are nonspecific immune responses

• The third line of defense, you immune system, reacts in specialized ways for various invaders

The First Line of Defense

• Mostly physical• Skin and mucous

membranes protect your body

• Acidic secretions keep skin at pH of 3-5

• Skin has acidic secretions that inhibit the growth of microbes

• Lysozyme, an antimicrobial enzyme, is secreted in tears, saliva, mucous and sweat.

Respiratory and Digestive System

• The respiratory passage is lined with mucous

• Cilia also lines the respiratory passage

• There is mucous in the respiratory passage that traps invading microbes and other foreign debris with the cilia.

• Acids in the stomach and protein digesting enzymes destroy most of the invading microbes carried into the body with food.

Immune System Overview: Goals

The Second Line of Defense

• Mobilized if an invader resides inside the body

• Leukocytes (white blood cells), engulf invading microbes, or produce antibodies

• Unlike red blood cells, white blood cells have a nucleus

Leukocytes• also called white blood cells are large opaque blood cells that engulf invading microbes. They can also produce antibodies.– They have a nucleus (so

different from red blood cells)– The size of the nucleus and

the types of granules that can be found inside of them can be used to classify them into different classes of leukocytes.

• Granulocytes: have cytoplasmic granules and are made in the bone marrow.

• Agranulocytes: do not have a granular cytoplasm and are also made in the bone marrow, but then modified in the lymph nodes.

Phagocytosis

• Non-specific defense mechanisms rely mainly on phagocytosis

• Monocytes migrate from the blood and into the tissues

• Macrophages extend pseudopods that grip the invading microbe

Neutrophils• Attracted to chemical signals emitted by

damage microbes

• Chemotaxis: A process where the neutrophils exit the capillaries and move toward the damaged tissue

• Lysosomal enzymes digest the microbe and the leukocyte

• The remaining fragments of protein, dead white blood cells and the digested microbes are called pus

Physical Injury

• Tissue damage initiates a localized inflammatory response– It is a nonspecific immune

response that results in swelling, redness, heat, and pain.

– Pus and inflammation are signs that the second line of defence has been at work.

System Wide Defense

• Injured cells emit chemicals that stimulate the production of phagocytic white blood cells, red blood cells and lymphocytes from the bone marrow

• Fever is another example of the body’s response to infection. – When you have infectious organisms in your

body, neutrophils and macrophages digest the invaders and release chemicals into the bloodstream

– When the chemicals reach the hypothalamus, they reset your body temperature to 40C in order to make it difficult for the bacteria to survive.