Immunity is the body’s natural defense against germs and substances that are harmful. The immune system is made up of organs, cells, and proteins that work together to protect the body from diseases. The immune system is also responsible for fighting cancer and other abnormal cell growth in the body.
The innate immune system is protection you’re born with, and it works quickly to respond to invaders. It creates physical barriers, such as the skin and mucous membranes that line the respiratory, gastrointestinal, and genitourinary tracts. These barriers stop germs, parasites (such as worms), and abnormal cells from entering the body. The innate immune system also includes immune system cells called natural killer cells and phagocytes, which fight these invading substances by attacking them.
An important function of the innate immune system is to help identify “antigens,” or substances that don’t belong in the body. Antigens are found on the surfaces of microbes, including viruses, bacteria, and fungi, as well as toxins produced by these organisms. Nonliving substances, such as a splinter or chemical, can also be antigens.
The adaptive immune system produces antibodies that are designed to specifically fight specific germs. It can be induced by infection with the disease organism or through vaccination. Once the body develops active immunity, it offers life-long protection against that particular disease. The adaptive immune system also keeps a memory of past encounters with disease organisms, so that the same germs won’t get a second chance to make you sick.
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