Health Information | Vitamin Maniac
Understanding The Immune System

By: Kristy Haugen
The immune system functions to protect the body from attack by infectious agents such as bacteria and viruses. The immune system has many complicated intricacies that can occur. Understanding how the immune system functions can help us understand how we protect ourselves from illness.

Acquired immunity involves production of recognition molecules that distinguish “self” from foreign (“nonself”) material. There are two forms of acquired immunity: cellular immunity and humoral immunity. Cellular immunity refers to the formation of lymphocytes that are sensitized against the invading agent. Humoral immunity involves binding of circulating antibodies to the invading agent.

Antibodies (immunoglobulins) are specific recognition molecules. An antibody consists of four polypeptide chains. There are two identical light chains and two identical heavy chains. This creates a Y-shaped molecule. Each light chain contains two domains: constant domain and variable domain. Each heavy chain contains two to three constant domains and one variable domain. The variable regions provide specificity which enables antibody to bind to a specific region of another molecule such as antigen. The constant regions provide a mechanism for binding of the antibody to other cells such as macrophages. The constant regions can also bind to elements of complement.

Antibodies bind to an antigen on an invading organism, marking the foreign material for destruction by either the complement system or by macrophages. The complement system (proteins) destroys infectious organisms by puncturing the cell membrane. Antibodies inactivate invading organism by clumping together (agglutination), precipitation, and neutralization (antibody binds to and covers a toxic site).

Lymphoid tissues are responsible for acquired immunity. This type of immunity will not develop until after contact is made with the invading agent. Lymphoid tissues are widely distributed throughout the body such as in lymph nodes, the thymus, the bone marrow, and the spleen. Lymphoid cells are white cells or lymphocytes of the blood.

Two types of lymphocytes exist: T-lymphocytes and B-lymphocytes. T-lymphocytes form the sensitized cells of the cellular immune system. B-lymphocytes are responsible for the production of antibodies in humoral immunity. T-cells contain a class of recognition molecules called T-cell receptors. T-cell receptors recognize cells that bear both “self” and “nonself” markers.

B- and T-lymphocytes arise from embryonic stem cells. However, before becoming part of the lymphoid tissues a maturation process is required. T-cells originate from the bone marrow but mature in the thymus gland. B-cells originate in the bone marrow but mature in the spleen, lymph nodes, and other lymphatic organs.

Q. How does the body respond to a viral infection?

A. A macrophage will ingest a virally infected cell. This will cause the macrophage to display a specific viral antigen on the cell surface. The specific viral antigen assists in marking the cell. Helper T-cells with the proper T-cell receptors will recognize the processed viral antigen on the macrophage surface. These helper T-cells will then become activated.

Activated helper T-cells will multiply. These cells stimulate the multiplication of killer T-cells and activated B-cells that can recognize the same processed viral antigen. Activated B-cells will multiply. These cells differentiate into plasma cells that produce antibodies to this viral antigen. A few of the B-cells will become memory cells. This creates a rapid response to any future infections by the same virus.

Killer T-cells destroy viral host cells (infected cells). Killer T-cells inhibit viral replication. B-cell antibodies will bind to the virus. This prevents the virus from infecting other host cells. Once the infection is contained, suppressor T-cells stop the immune response. In case of future infections with this virus, memory T-cells and B-cells will remain in the blood and lymphatic system. In correspondence, the AIDS virus is damaging to the immune system because of its ability to invade and kill the helper T-cells.

In order to keep the body’s immune system function, the body needs to be at optimal health. Optimal health requires the necessity of a well-balanced diet and exercise program. Many experts agree in the importance of a vitamin supplement. This is one way to keep the body healthy.

References

1. Champe, Pamela C; Harvey, Richard A; and Ferrier, Denise R. Lippincott’s Illustrated Reviews: Biochemistry. 3rd ed. Lippincott Williams &Wilkins. Philadelphia, Pennsylvania. 2005.
2. Parham, Peter. The Immune System. New York, NY. Current Trends and Garland Publishing. 2000.
3. McKinley, Michael P. and O’Loughlin, Valerie Dean. Human Anatomy. 1st ed. New York, NY. McGraw-Hill. 2005.

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