1. The Immune Response

2. The Third Line of Defense The third line of defense involves a specific response that is effective against specific pathogens. This involves a specialized group of white blood cells called lymphocytes, which produce antibodies. Antibodies are protein molecules that protect the body from invaders.

3. The Third Line of Defense (cont’d) All cells have special markers located on their cell membranes, which are known as antigens (antibody generator). Normally, the immune system does not react to the body’s own markers. However, intruding cells or foreign proteins activate the production of antibodies.

4. The Third Line of Defense (cont’d) There are two different types of lymphocytes found in the immune system. The first is the T cell, which is produced in the bone marrow and is stored in a tiny organ called the thymus gland. The T cell’s function is to seek out the intruder and signal the attack. Acting much like a sentry, some T cells identify the invader by its antigen markers.

5. The Third Line of Defense (cont’d) Once the antigen is identified, another T cell passes this information on to the antibody producing B cell. B cells multiply and produce chemical weapons: the antibodies. Each B cell produces a single type of antibody.

6. Antigen-Antibody Reactions Antibodies are Y-shaped proteins that are produced to target specific foreign invaders. Antibodies are specific; this means that an antibody produced against the influenza virus is not effective against HIV. Each antibody has a shape that is complementary to its specific antigen.

7. Antigen-Antibody Reactions (cont’d) There are many different antigen markers on the membrane of a virus or bacterium. The attachment of antibodies to the antigens increases the size of the complex, making the antigen-antibody combination more conspicuous and, therefore, more easily engulfed and destroyed by macrophages.

8. Immune Response Step 1: Pathogen enters body.

9. Immune Response (cont’d) Step 2: Macrophages engulf pathogen and pushes the antigen markers to its outer membrane.

10. Immune Response (cont’d) Step 3: A helper T-cell identifies the antigen present on the cell membrane of the macrophage.

11. Immune Response (cont’d) Step 4: Helper T cells alert the B cells, which multiply and begin to produce antibodies.

12. Immune Response (cont’d) Step 5: Antibodies attach to the antigens.

13. Immune Response (cont’d) Step 6: Antibodies immobilize and tag invaders for macrophages to destroy.

14. Immune Response (cont’d) Step 7: Helper T cells also send out chemicals to stimulate killer T cells. Killer T cells puncture the cell membranes of intruders. If killer T cells find a viral coat attached to a cell membrane, the T cell attacks the infected cells.

15. Immune Response (cont’d) Step 8: During the immune response, memory B cells and memory T cells are created. These cells contain a blueprint of the invader’s antigen. This will allow the immune system to react faster the next time that particular antigen enters the body.

16. Immune Response (cont’d) Step 9: A suppressor T cell ends the battle by signaling the immune system to return to its pre-infection state.

17. Immune Response Step 1: Pathogen enters the body. Step 2: Macrophages engulf pathogen and pushes the antigen markers to its outer membrane. Step 3: A helper T-cell identifies the antigen present on the cell membrane of the macrophage. Step 4: Helper T cells alert the B cells, which multiply and begin to produce antibodies. Step 5: Antibodies attach to the antigens. Step 6: Antibodies immobilize and tag invaders for macrophages to destroy. Step 7: Helper T cells also send out chemicals to stimulate killer T cells. Step 8: During the immune response, memory B cells and memory T cells are created. Step 9: A suppressor T cell ends the battle by signaling the immune system to return to its pre-infection state.

18. Components of the Immune Response