Final answer:
Lymph nodes contain immune cells such as B cells, T cells, and natural killer (NK) cells, along with macrophages and dendritic cells which capture and present antigens to initiate an immune response.
Step-by-step explanation:
Lymph nodes are critical components of the lymphatic system, serving as filters for foreign particles and as a key site for immune system activation. The main types of cells contained within lymph nodes are lymphocytes, which include B cells, T cells, and natural killer (NK) cells. These lymphocytes have large central nuclei surrounded by a thin layer of cytoplasm and are distinguished by their surface protein markers and the molecules they secrete.
B cells are involved in the production of antibodies and can rapidly divide to form germinal centers. T cells, on the other hand, are crucial for cell-mediated immunity and play a pivotal role in the activation of other immune cells. NK cells provide a first line of defense with their ability to recognize and destroy various infected or abnormal cells. In addition, lymph nodes also contain macrophages and dendritic cells, which capture and present antigens to T cells, initiating an immune response.
The lymph enters the lymph node through afferent lymphatic vessels and flows through the subcapsular sinus—occupied by dendritic cells, macrophages, and reticular fibers—before reaching the inner regions. Within the lymph node's cortex are the lymphoid follicles that comprise the germinal centers with B cells and a surrounding layer of T cells. The medulla contains bands of B cells and plasma cells, within which the lymph is collected before exiting the lymph node via efferent lymphatic vessels.