Chapter 40-2 Notes

The Immune System



The function of the immune system: to fight infection through the production of cells that inactivates foreign substances or cells.


There are two categories of defense mechanisms against infection:

1. Non-specific defenses

2. Specific defenses


Nonspecific Defenses: Do not discriminate between one threat and another; they are always working.



§    Skin: creates a physical barrier.

§    Mucus/Saliva/Tears: contains enzymes that break down the cell walls of many bacteria.

§    Sweat Glands: creates an acidic environment to kill bacteria.

§    Inflammation: a response to tissue damage caused by injury or infection.

§    Fever: immune system releases chemicals that increase the core body temperatures that many pathogens cannot survive in.

§    Interferons: proteins produced by the body in response to a viral infection that helps block viral replication.


Specific Defenses:


Immune Response: a series of specific defenses that attack the particular disease-causing agent. 


There are two types of Specific Defenses:

1. Humoral Immunity: involves B cells

2. Cell-Mediated Immunity: involves T cells


Humoral Immunity: defense against pathogens in body fluids



1. The pathogen enters the body.

2. The pathogens contain antigens on its surface which are substances that trigger the immune response.

3.  The macrophage (a type of white blood cell) engulfs the pathogen and places the pathogen’s non-self antigens on the surface of the macrophage.

4.  Helper T-cells bind to the antigens on the surface of the macrophage which causes them to activate.

5. The activated helper T-cells activate the B-cells.

6. B-cells recognize the antigens as foreign and divide producing plasma B-cells and memory B-cells.

7. Plasma cells release antibodies.

8. Antibodies are proteins that bind to antigens to destroy the pathogen.

Antibodies and antigens must fit like a “lock and key”.  They have a complementary shape.


9. The memory B cells stay in the body for life for a second encounter.






How HIV damages T-cells:

Figure 6

Figure 7


Cell-Mediated Immunity: defense against pathogen inside cells and cancer cells.

1. White blood cells called phagocytes or macrophages engulf infected cells and display the antigens on their surface.

2. Helper T-cells bind to the phagocyte and stimulate the production of killer T-cells, memory T-cells, and suppressor cells.

3. Killer T-cells: disrupts the cell membranes of infected cells and destroys them.


4. Memory T-cells: (like memory B cells) remain in body for another encounter.

5. Suppressor T-cells: shut down the killer T cells once the pathogen is brought under control.


The killer T cells make it difficult for organ transplants because they often attack the tissue as being foreign and cause organ rejection from the recipient.  Recipients must take drugs to suppress the cell-mediated immune response.


Primary VS Secondary Immune Response:


1. Primary: first time the pathogen enters the body:

§    Slow response

§    Usually see symptoms

2. Secondary: second time the exact same pathogen enters the body:

§    Faster response because memory cells already there.

§    Usually don’t get symptoms