What role does the spleen play in the immune response?

The spleen plays a crucial role in the immune response primarily through its functions in filtering blood and removing old red blood cells, as well as producing antibodies. Located in the upper left abdomen, the spleen acts as a blood reservoir and a site for immune system activation.

When blood flows through the spleen, it passes through various compartments where immune cells, such as lymphocytes and macrophages, are present. The spleen helps identify and respond to pathogens, filtering out debris and old or damaged red blood cells. Specifically, the white pulp of the spleen is involved in the immune response, where B cells can produce antibodies against antigens encountered in the blood. This process is essential for mounting an effective adaptive immune response.

On the other hand, other options presented do not accurately describe the functions of the spleen. Insulin production is a function of the pancreas, not the spleen. The spleen does not store nutrients or regulate appetite, nor does it absorb vitamins directly from the digestive system; those functions are more associated with the intestines and other organs involved in nutrient absorption. Thus, the correct answer highlights the primary immune-related functions of the spleen.