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

Those at greatest risk of having latent TB become an active infection are those who’ve been exposed to someone with active TB, people who have weakened immune systems from diseases such as HIV and diabetes, and young children under 5 years old. —Chase Hunter, Mercury News, 9 Mar. 2026

Key Takeaways In OSA, the complex interplay between intermittent oxygen deprivation, oxidative stress, and sympathetic nervous system overactivity generates a vicious cycle that weakens the immune system and fosters low-grade inflammation. —Daniel Combs, Verywell Health, 9 Mar. 2026

The appendix supports the immune system. —Lilia Goncharova, The Conversation, 9 Mar. 2026

Autoimmune conditions, such as alopecia areata, also factor into hair thinning by causing the immune system to attack hair follicles and drive hair loss, according to the National Institutes of Health. —Nicole Fallert, USA Today, 8 Mar. 2026

Word History

First Known Use

1899, in the meaning defined above

Rhymes for immune system

• cryptosystem
• ecosystem
• intersystem
• multisystem
• photosystem
• subsystem

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