The immune system is the human body’s natural defense against infection. It is comprised of two main parts, the innate and the adaptive, and it protects the body from harmful foreign material called antigens. Non-living organisms have antigens and the immune system detects these antigens and kills them. The body’s nonspecific defenses include the skin and mucus. These body fluids contain enzymes that kill pathogens. The second part of the immune system protects the body from disease by recognizing its own normal antigens and destroying them.
The immune system also protects the body against infection by protecting the tissues from damage caused by bacteria. In addition to killing bacteria, body fluids contain anti-bacterial enzymes that help the body eliminate infections. The immune system also reacts to allergies by producing histamines, which trigger an allergic reaction. Allergic reactions are often mild, but there are some cases where the body reacts severely and needs antihistamine medication.
In a common cold, the immune system activates when exposed to an antigen, which can be a microbe, a chemical, or an object outside the body. Antigens attach to the special receptors on immune cells and trigger a series of processes. Antibodies attach to antigens and fight off the invader germ. If the virus or bacteria attacks the immune system, the cells that fought the infection remember and fight the pathogen more effectively.