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

The products are predominantly used on newborns, infants and young children who are vulnerable to infection due to their immature immune systems, the federal agency said. —Nick Lentz, CBS News, 6 June 2026

Salmonella can cause serious and sometimes fatal infections, particularly in young children, older adults and people with weakened immune systems. —Angelique Brenes, PEOPLE, 5 June 2026

His immune system, no longer overwhelmed by runaway viral replication, then regained the upper hand and finished the virus off on its own. —Elie Dolgin, IEEE Spectrum, 4 June 2026

For a stronger microbiome and immune system, there isn’t one superfood that will make the difference –– the keys are balance, variety and consistency. —Madeline Holcombe, CNN Money, 3 June 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