Lymph nodes are populated predominantly by macrophages, dendritic cells,B lymphocytes, and T lymphocytes. B lymphocytes are located primarily in the follicles and perifollicular areas, T lymphocytes are found primarily in the interfollicular or paracortical areas of the lymph node.In young children palpable lymphadenopathy is the rule who are continuously undergoing exposure to new antigens, In fact, the absence of palpable lymphadenopathy would be considered abnormal. In adults, lymph nodes larger than 1 to 2 cm in diameter are generally considered abnormal.

Generalized immune proliferation and lymphadenopathy can occur with a systemic disorder of the immune system,disseminated infection,or disseminated neoplasia. Malignancies of the immune system might be manifested as:localized or disseminated lymphadenopathy.

Bacterial (e.g., all pyogenic bacteria, cat-scratch disease, syphilis,tularemia)
Mycobacterial (e.g., tuberculosis, leprosy)
Fungal (e.g., histoplasmosis, coccidioidomycosis)
Chlamydial (e.g., lymphogranuloma venereum)
Parasitic (e.g., toxoplasmosis, trypanosomiasis, filariasis)
Viral (e.g., Epstein-Barr virus, cytomegalovirus, rubella, hepatitis, HIV)
Benign disorders of the immune system (e.g., rheumatoid arthritis, systemic lupus erythematosus, serum sickness)
Drug reactions such as to phenytoin,
Castleman's disease, sinus histiocytosis with massive lymphadenopathy, Langerhans'cell histiocytosis,
Kawasaki syndrome, Kimura's disease 
Malignant disorders of the immune system (e.g., chronic and acute myeloid and
lymphoid leukemia, non-Hodgkin's lymphoma, Hodgkin's disease, angioimmunoblastic-like
T-cell lymphoma, Waldenström's macroglobulinemia, multiple myeloma with amyloidosis, malignant histiocytosis)
Other malignancies (e.g., breast carcinoma, lung carcinoma, melanoma, head and
neck cancer, gastrointestinal malignancies, germ cell tumors, Kaposi's sarcoma)
Storage diseases (e.g., Gaucher's disease, Niemann-Pick disease)
Endocrinopathies (e.g., hyperthyroidism, adrenal insufficiency, thyroiditis)
Miscellaneous (e.g., sarcoidosis, amyloidosis, dermatopathic lymphadenitis)

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