What organs are immune cells produced?

Immune cells are primarily produced in the bone marrow. This is where hematopoiesis occurs, the process through which all blood cells, including red blood cells, white blood cells, and platelets, originate from hematopoietic stem cells. Specifically, various types of white blood cells, such as lymphocytes (which include T cells and B cells) that play crucial roles in the immune response, are generated in the bone marrow and subsequently mature in other organs.

While the tonsils, spleen, and lymph nodes are important components of the immune system, as they help to filter pathogens and serve as sites for immune activation, they do not serve as the primary production site for immune cells. Therefore, the bone marrow is the correct choice as the major organ responsible for the production of these vital cells.