Function of the Spleen
The spleen serves as the body's primary blood filter and immune defense organ, performing three critical functions: filtering blood-borne pathogens and abnormal cells, producing antibodies against encapsulated bacteria, and removing old or damaged red blood cells from circulation. 1, 2, 3
Primary Immunologic Functions
The spleen operates as the largest secondary lymphoid organ in the body, uniquely combining innate and adaptive immunity through its specialized architecture 2, 3:
- Phagocytic filtration: The spleen removes bacteria and cellular debris from the bloodstream, particularly targeting poorly opsonized organisms that the liver cannot efficiently clear 1
- Antibody production: The organ produces opsonizing antibodies essential for rapid bacterial clearance, making it the most important organ for antibacterial and antifungal immune responses 1, 2
- Antigen presentation: The spleen facilitates low-probability interactions between antigen-presenting cells and cognate lymphocytes, initiating adaptive immunity to blood-borne antigens 3
Hematologic Functions
Beyond immunity, the spleen maintains blood cell homeostasis 4, 5:
- Erythrocyte clearance: The spleen filters and removes old or damaged red blood cells from circulation 2, 5
- Iron metabolism: The organ plays a key role in iron recycling and metabolism 4
- Hematopoiesis: Recent evidence suggests the spleen has additional hematopoietic functions beyond traditional understanding 4
Structural Organization
The spleen's unique architecture enables its dual functions through two distinct compartments 3, 5:
- White pulp: Houses lymphoid tissue responsible for initiating immune reactions to blood-borne antigens, including the marginal zone where initial pathogen capture occurs 3, 5
- Red pulp: Performs blood filtration, removing foreign material and damaged cells through its specialized vascular organization 5
Clinical Significance of Splenic Function
The critical importance of splenic function becomes evident when the organ is absent or dysfunctional 6, 7:
- Overwhelming post-splenectomy infection (OPSI): Loss of splenic function creates lifelong risk of fulminant bacterial infections, particularly from encapsulated organisms like Streptococcus pneumoniae (50% of cases), Neisseria meningitidis, and Haemophilus influenzae type b 6, 7
- Infection rates: Children under 5 years have infection rates exceeding 10% after splenectomy, compared to less than 1% in adults, reflecting the spleen's critical role in developing immunity 6, 7
- Functional hyposplenism: Conditions like sickle cell disease, celiac disease, and inflammatory bowel disease can cause splenic dysfunction detectable by Howell-Jolly bodies on blood film, requiring identical preventive measures as surgical splenectomy 6, 7
Common Pitfalls
Do not underestimate the spleen's role in immunity—even partial splenic preservation through angioembolization maintains immunologic function, as evidenced by preserved immunoglobulin titers despite elevated leukocyte and platelet counts 6. The spleen's intense vascularization allows continued immunological function even after partial injury 6.