A 25-year-old woman is transported to the emergency department by emergency medical services with multiple injuries from a motor vehicle accident. Her vitals show blood pressure of 80/50 mm/Hg, heart rate of 150 beats/minute, and respirations of 27/minute. Physical examination shows multiple abrasions and obvious deformities of the right wrist and right knee. There is an ecchymosis of the left upper quadrant of the abdomen. A CT scan demonstrates a ruptured spleen. The patient is taken to the operating room, and she undergoes a splenectomy. After the surgery, the patient is counseled on the importance of vaccinations against encapsulated bacteria.
Through which of the following mechanisms does the spleen protect against these organisms?
D: Opsonization of bacteria with antibodies which are then phagocytosed by macrophages
The spleen is the largest secondary lymphoid organ in an adult human and is made up of red and white pulp. In the white pulp, infectious antigens are presented by antigen-presenting cells to activate T-cells and B-cells, which eventually leads to the production of opsonizing antibodies. Encapsulated bacteria are able to evade the immune system due to their unique polysaccharide capsule. However, opsonization of bacteria with antibodies makes them visible to the immune system. After opsonization, macrophages, dendritic cells, and neutrophils are able to phagocyte antigens and clear infection.
Answer choice A: Collective cord of Billroth filtration system, is incorrect. The cord of Billroth system makes up the red pulp. They filter blood and cause phagocytosis of infected erythrocytes which helps to form a defense against intraerythrocytic parasites such as babesiosis and malaria.
Answer choice B: Fas ligands of T cells binding leading caspase activation, is incorrect. This is the mechanism of apoptosis of normal cells via the extrinsic signaling pathway. Fas ligands on activated T cells bind to Fas receptors on the cells to initiate apoptosis via caspase (protease) enzyme activation.
Answer choice C: Macrophage receptors recognize and bind with bacteria capsule antigen, is incorrect. The capsule of encapsulated bacteria is made up of polysaccharide which helps the bacteria evade complement deposition and phagocytosis by cells such as macrophages.
Answer choice E: Spleen lipase reacts with bacterial liposaccharides, is incorrect. This is the splenic mechanism for protection against Gram-negative bacteria, not encapsulated bacteria specifically.
Key Learning Point
The spleen has many functions including 1) Filtration of old and abnormal erythrocytes and platelets via splenic cords in the red pulp; 2) Iron recycling and storing; 3) Extramedullary hematopoiesis to assist the bone marrow to compensate for hemolytic situations; and 4) Infection prevention by phagocytosis of the filtered blood and production of opsonizing antibodies.
