Lymphocytosis
Lymphocytosis: > 33%
Etiology
- Acute viral infections (e.g., rubella, infectious mononucleosis, mumps)
- Chronic infections (e.g., tuberculosis, syphilis, toxoplasmosis)
- Neoplasia (e.g., Hodgkin lymphoma, non-Hodgkin lymphoma, CLL)
Tip
The lymphocyte count may be increased or decreased in lymphoma.
T cell differentiation
Lymphatic system
Lymph nodes
Function
- Nonspecific lymph filtration: macrophages within lymph node
- Storage and circulation of B cells and T cells
- Immune system activation: Antigen presentation induces differentiation and proliferation of B lymphocytes and activation of T lymphocytes.
Structure
Clinical significance
- Inflammatory or immune reactions (e.g., due to EBV infection) → reactive paracortical hyperplasia → clinically apparent lymphadenopathy
- Depletion of paracortical lymphocytes: DiGeorge syndrome