Which organ is primarily responsible for immune responses?

The spleen is primarily responsible for immune responses due to its crucial role in filtering blood and managing the body's immune functions. It contains various types of white blood cells, including lymphocytes and macrophages, which help identify and eliminate pathogens such as bacteria and viruses. The spleen acts as a reservoir for blood and filters out old or damaged red blood cells while also producing antibodies and activating immune responses when foreign substances are detected.

In addition to producing and storing immune cells, the spleen plays a pivotal role in initiating the immune response for systemic infections. It facilitates the interaction of antigens with immune cells, enhancing the effectiveness of the body's defense mechanisms. The significance of the spleen in the immune system can be seen in conditions where it is removed (splenectomy), leading to increased susceptibility to infections.

While organs like the liver, kidneys, and pancreas have important functions in metabolism, detoxification, and digestion, they do not primarily drive immune responses in the same direct and specialized manner as the spleen.