The immune system is a group of cells, molecules, and tissues that help defend the body against diseases and other harmful invaders. The immune system provides protection against a variety of potentially damaging substances that can invade the body. These substances include disease-causing organisms, such as bacteria, fungi, parasites, and viruses. The body's ability to resist these invaders is called immunity. A key feature of the immune system is its ability to destroy foreign invaders …showed first 75 words of 733 total…

…showed last 75 words of 733 total…The process of inducing an immune response is called immunization. It may be either natural, through infection by a pathogen, or artificial, through the use of serums or vaccines. The immune system cannot protect the body from diseases by itself. Sometimes it needs help. Physicians give their patients vaccines to help protect them from certain severe, life-threatening infections. Vaccines and serums boost the body's ability to defend itself against particular types of viruses or bacteria.