Monday April 12,1999
Announcements: Review session tonight in 110 Wartick

Lecture notes:

The immune system comprises you body's defense against invasion. There are three lines of defense, each line of defense becoming more specific for a particular invader.

First line of defense: barriers

Second line of defense: a. phagocytes

b. "complement"

c. inflammation

Third line of defense: a. anitbodies

b. cell mediated immunity

1. Intact skin
2. Cilliated mucous membranes a. mucus catches "junk"
   b. cilia sweep it out.
3. Secretions from exocrine glands on epithelial tissue. (lysozyme in tears)
4. Gastric fluid
5. "Flora" of microbes in the gut and in the vagina in females. They prevent the overgrowth of bacteria.

These cells originate in bone marrow from stem cells. These include:

1. neutrophils
2. monocytes (monocytes mature into "big eater" cells called macrophages)

Phagocytes engulf foreign cells and other substances by endocytosis.

Some circulate in the blood and can squeeze through the walls of capillaries to get to the invaders.

Some live in lymph nodes and spleen.

Some are in internal organs (liver and kidney) and in joints.

1 in 100 cells in your body is a white blood cell.

The complement system has a set of plasma proteins that enhance nonspecific and specific immune responses. They are secreted in an inactive form and activated where they are needed.

It is divided into "early" and "late" components, which travel in and inactive form.

Activation by foreign cells causes the "first" complement protein (C1) to change from its proenzyme form to its active form.

Active C1 cleaves other proteins and starts the "Cascade"

The early components create chemical gradients that attract phagocytes to the site.

Others form a coat on foreign cells that attracts phagocytes.

Late components form large proteins that disrupt membranes and kill foreign cells.

The purpose if inflammation is to destroy invaders and restore tissues to normal.

Inflammation occurs in both non-specific and specific defense responses.

Players:

Basophils: derived from myeloid stem cells in bone marrow. They circulate in the blood stream.

Mast cells: also derived from the myeloid stem cells in bone marrow. These are tissue bound (in glands, near blood vessels, lining the lungs and in nerves)

Events:

1. Invasion
2. Identification of a "foreign" substance by a mast cell or basophil.
3. Release of histamine
4. Histamine dilates blood vessels and causes seepage of fluid into tissues.
5. Vasodilation causes warmth and redness.
6. Seepage of fluid causes swelling.
7. Seepage also causes leakage of "complement" into the area.
8. Phagocytes follow the chemical trail to damaged tissue and engulf invaders and cellular debris.
9. Agents involved in clotting wall off the infection to keep it from spreading.
10. Tissues are repaired after inspection stopped.

This system mounts the most efficient attack.

The cells involved have 2 unique properties: specificity and memory

The system has 2 branches - both of which are active during most invasions.

The main actors are B and T lymphocytes. The supporting cast includes natural killer cells and macrophages.

Remember: the origin of lymphocytes are the lymphocyte stem cells in the bone marrow.

B-cells stay and mature in the bone marrow.

T-cells travel to the thymus and mature there.

B-cells are involved in the Antibody-Mediated Immune Response.

Killer T-cells are involved in the Cell-Mediated Immune Response.

Helper T-cells are involved with both.

How can the immune system tell the difference between its own tissue and "foreign" tissue?

MHC marker proteins identify "self". These proteins, "major histocompatibillity complex" marker proteins are on the plasma membrane of all body cells. Lymphocytes ignore them - they are self.

NON-SELF = Antigen

An antigen is a macromolecule (usually a protein of polysaccharide) that is recognized as foreign and triggers an immune response.

The word antigen comes from antibody generating.