Which organs or systems are mainly responsible for producing specific lymphocytes and plasma cells in response to circulating antigens?

The lymph nodes and spleen play pivotal roles in the immune response by producing specific lymphocytes and plasma cells when exposed to circulating antigens. Lymph nodes are strategically located throughout the body and act as filters for lymph fluid, where they trap pathogens and foreign particles. They contain specialized areas where B cells and T cells can be activated and proliferate in response to antigens.

The spleen serves a similar function for blood-borne antigens, filtering the blood and facilitating responses to pathogens. In both organs, B lymphocytes can differentiate into plasma cells, which produce antibodies against specific antigens. This antibody production is crucial for the adaptive immune response, providing long-term immunity.

Other organs mentioned, such as the liver and kidneys, primarily have roles in metabolic processes and waste elimination rather than direct involvement in the immune response to antigens. The heart and lungs are vital for circulation and gas exchange, but they do not produce lymphocytes or plasma cells. The skin and mucous membranes act as physical barriers and can initiate immune responses, but they are not the primary production sites for lymphocytes and plasma cells, which is why the lymph nodes and spleen are the correct answer.