Where are macrophages and lymphocytes that filter lymph typically located?

Macrophages and lymphocytes that filter lymph are primarily found in lymph nodes. Lymph nodes serve as crucial sites for the immune response, where lymph—a fluid containing immune cells, proteins, and waste—is filtered. Within the lymph nodes, macrophages play a vital role in engulfing pathogens and debris, while lymphocytes, including T cells and B cells, are essential for targeting and responding to specific antigens.

Both of these cell types work together in the lymph nodes to ensure that the lymph is thoroughly examined for harmful organisms before it can continue to circulate back into the bloodstream. This strategic location maximizes the body's ability to detect and respond to infections or foreign substances early on. The role of lymph nodes in this process is so significant that they act as major hubs in the lymphatic system and serve as critical components of the adaptive immune response.

In contrast, other options like the spleen, bone marrow, and thymus have different functions related to the immune system but do not primarily filter lymph. The spleen is involved in filtering blood and managing blood cells, the bone marrow is the site of blood cell production, and the thymus serves as the maturation site for T lymphocytes.