Which of the following is NOT a function of the spleen?

The spleen plays several critical roles in the body's immune system and blood regulation, but producing white blood cells is not a primary function attributed to the spleen. Instead, while the spleen does contain a variety of immune cells and helps modulate immune responses, the bulk of white blood cell (WBC) production occurs in the bone marrow.

Moreover, the spleen does engage in important immune functions, such as filtering blood and responding to pathogens, hence contributing to the adaptive and innate immune responses. It stores blood, recycles iron from hemoglobin in old red blood cells (RBCs), and filters out aged and damaged RBCs, ensuring an efficient regulatory function.

Understanding these roles highlights the distinction between the spleen's involvement in immune system regulation versus its function in the production of white blood cells, which primarily occurs elsewhere in the body.