Secondary lymphoid organs

Definition

Secondary lymphoid organs are tissues where lymphocytes, a type of white blood cell, are activated to fight infection. They include the lymph nodes, spleen, tonsils, and Peyer's patches in the small intestine.

Related terms

Lymph nodes: Small, bean-shaped structures that filter lymph fluid and house immune cells that can attack pathogens.

Spleen:

An organ that filters blood, removing old red blood cells and hosting immune responses against blood-borne pathogens.

Tonsils: Clusters of lymphoid tissue at the back of the throat that act as a first line of defense against ingested or inhaled pathogens