Your immune system protects you from germs, diseases, and other harmful substances. It’s made up of special parts of your body, such as the thymus, spleen, lymph nodes, special deposits of lymphoid tissue in the groin and scrotum, and bone marrow, plus cells called lymphocytes including B cells and T cells. These cells, along with antibodies, fight off invaders and heal your body from infection.
You have natural immunity that’s already in place from the day you’re born. It’s called innate immunity, and it protects you from germs, bacteria, viruses, and even nonliving substances (such as poisons or toxins) that might cause disease.
Innate immunity works by recognizing and attacking anything that shouldn’t be in your body, such as germs or foreign substances. The white blood cells that make up innate immunity don’t need any previous training to tell the difference between cells that belong in your body and those that aren’t. They also don’t offer protection against specific germs in the future, but they do keep track of the antigens of a particular pathogen that they encounter for the first time.
When enough people in a community become immune to a particular pathogen, it cannot spread as easily. This is known as herd immunity and it can help prevent illness in people who haven’t received immunizations or whose immunity is weakened by cancer treatment. Herd immunity also makes it easier for medical professionals to give vaccinations, such as those against measles, whooping cough, and influenza.
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