immune system

noun

: the bodily system that protects the body from foreign substances, cells, and tissues by producing the immune response and that includes especially the thymus, spleen, lymph nodes, special deposits of lymphoid tissue (as in the gastrointestinal tract and bone marrow), macrophages, lymphocytes including the B cells and T cells, and antibodies

Examples of immune system in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
People who have compromised immune systems could see their symptoms persist. — Brenda Goodman, CNN Money, 7 July 2026 This loss is often the result of an autoimmune process in which the body's immune system mistakenly attacks those cells. — Daryl Austin, USA Today, 8 July 2026 Patients who receive new organs must take medication to suppress their immune systems, which can lead to a recurrence if any cancer cells are left in the body. — Chicago Tribune, 8 July 2026 Harmful molecules called free radicals show up, certain enzymes start breaking down collagen and the immune system is activated. — Leslie Baumann, Miami Herald, 9 July 2026 See All Example Sentences for immune system

Word History

First Known Use

1899, in the meaning defined above

Time Traveler
The first known use of immune system was in 1899

Rhymes for immune system

See All Rhymes for immune system

Browse Nearby Words

immune surveillance
immune system
immunist
See all Nearby Words

Cite this Entry

“Immune system.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/immune%20system. Accessed 10 Jul. 2026.

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Kids Definition

immune system

noun
: the bodily system that protects the body from foreign substances, cells, and tissues by producing the immune response and that includes especially the thymus, spleen, lymph nodes, lymphocytes, and antibodies

Medical Definition

immune system

noun
: the bodily system that protects the body from foreign substances, cells, and tissues by producing the immune response and that includes especially the thymus, spleen, lymph nodes, special deposits of lymphoid tissue (as in the gastrointestinal tract and bone marrow), lymphocytes including the B cells and T cells, and antibodies

More from Merriam-Webster on immune system

Nglish: Translation of immune system for Spanish Speakers

Britannica.com: Encyclopedia article about immune system

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