Final answer:
The correct answer to the question about the spleen is that it contains a marginal zone rich in macrophages and dendritic cells, which are crucial for the immune response. It filters blood and plays a role in trapping pathogens and antigens, rather than filtering lymph or containing the pancreas and adrenal glands.
Step-by-step explanation:
The spleen is a secondary lymphoid organ that plays a vital role in the immune response to blood-borne pathogens. It is equipped with a marginal zone rich in macrophages and dendritic cells which serve as antigen-presenting cells (APCs). These APCs are crucial for the activation of T lymphocytes and B lymphocytes. The spleen filters blood rather than lymph, trapping pathogens and antigens that pass into it, and it contains a specialized environment for the immune functions, including the formation of antibodies by activated plasma cells.
Contrary to some misconceptions, the spleen does not include the pancreas or the adrenal glands, nor does it contain many neutrophils, which are more commonly associated with acute inflammation and are typically found in the blood and in sites of infection. Therefore, the correct answer to this question is: A. contains a marginal zone rich in macrophages and dendritic cells.