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

Listeria monocytogenes is a bacterium that can cause serious infections, particularly in pregnant people, young children, older adults and those with weakened immune systems, according to the Centers for Disease Control and Prevention (CDC). —Moná Thomas, PEOPLE, 20 Jan. 2026

This reduces the effectiveness of dendritic cell vaccines, an immunotherapy that trains the immune system to attack cancer, according to the study. —Khloe Quill, FOXNews.com, 20 Jan. 2026

When the body encounters cedar pollen, the immune system releases a cascade of inflammatory chemicals. —Miriam Fauzia, Dallas Morning News, 20 Jan. 2026

Blood and saliva sampling to measure immune biomarkers and examine how space alters the immune system. —Matthew Glasser, ABC News, 20 Jan. 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