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

Your immune system needs iron to fight infections, and your body uses iron to make hemoglobin, the protein in red blood cells that carries oxygen from your lungs to other organs and tissues. — Anahad O’Connor, Washington Post, 27 Aug. 2026

The gut microbiome can affect our brains by changing our immune systems and our metabolism, Cox said. — Norah O'Donnell, CBS News, 26 Aug. 2026

The immune system has been implicated in several medical conditions, including mood disorders such as depression. — Anand Kumar, The Conversation, 26 Aug. 2026

With up to nine doses of Keytruda, infused every six weeks, plus up to nine doses of the customized mRNA vaccine, the treatment trains the immune system to recognize and attack cancer cells. — Mariam Sunny, USA Today, 25 Aug. 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