Innate body defenses to disease include surface membrane barriers, such as the skin and mucous membranes, as the first line of defense. Not only do the skin and mucous membranes act as a physical barrier to microorganisms, but they also secrete chemicals such as saliva, sebum, mucus, and HCl that kill microorganisms. Innate cellular defenses include the use of phagocytes and natural killer cells. Inflammation occurs in response to injury. The inflammation response includes vasodilation, increased vascular permeability, and phagocyte mobilization. Antimicrobial substances such as interferon and complement are also produced as innate defenses by the body.

Regulatory T cells important to the immune process - They are vital in the final stopping of an immune response after the antigen is inactivated. They may also help prevent autoimmune reactions.

Children born without a thymus must be kept in a germ-free environment if they are to survive. Explain why this is necessary.
If the thymus fails to develop, the T cells will not mature and become immunocompetent. If T cell function is disrupted, there is no resistance to disease.

What are the signs of inflammation, and how does inflammation serve as a protective function?
The four signs of inflammation are swelling, redness, heat, and pain. The signs are caused by local vasodilation and increased capillary permeability. This is of benefit because the process helps to dilute harmful substances that may be present; brings in large quantities of oxygen, nutrients, and cells necessary for the repair process; and allows the entry of clotting proteins. Pain helps immobilize the injury.

1. Cytotoxic T cells (CD8, MHC I) are the only T lymphocytes that can directly attack and kill other cells.
2. The antibody that becomes bound to mast cells and basophils and causes the cells to release histamine and other chemicals is IgE.
3. Harmful or disease-causing microorganisms are called pathogens.
4. Natural killer cells can lyse and kill cancer cells and virus-infected body cells before the immune system is activated.
5. What is the role of interferon in defense against disease - protects cells that have not yet been infected by viruses.
6. T cells - their proliferation is enhanced by interleukins 1 and 2.
7. Most critical cell in immunity - helper T cell.
8. Function of antibodies - complement fixation is the main mechanism by which antibodies provide protection.
9. The primary immune response - has a lag period while B cells proliferate and differentiate into plasma cells.
10. Clonal selection of B cells - results in the formation of plasma cells.
11. Natural killer (NK) cells - can kill cancer cells before the immune system is activated.
12. Helper T cells - function in the adaptive immune system activation.
13. Cytotoxic T cells - are the only T cells that can directly attack and kill other cells.
14. Active and passive immunity - active and passive humoral immunity are both mechanisms of adaptive immunity that use antibodies.
15. Immunocompetence - is the ability of individual cells to recognize a specific antigen by binding to it.
16. Fever - production is regulated by chemicals that reset the body's thermostat to a higher setting.
17. Phagocyte mobilization involves - mainly