Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Normal

NK Cell*


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› Microscopic Features:

• Slightly larger than a mature RBC
• High nuclear to cytoplasmic ratio but with a
• Round mature Nucleus (clumped chromatin)
• Nucleoli are absent
• Cytoplasm may have some granules

› Normal % blood-PB, marrow-BM, lymphoid tissue-LN:

• PB: Rare scattered (Note that lymphocytes in general are the 2nd most common WBCs in blood. Majority are T-cells, followed by scattered B-cells and rare scattered NK-cells)
• BM: Rare scattered
• LN: Rare scattered

› May Resemble:

• Mature T-cell (can't distinguish it from mature T-cell or B-cells based on morphology)
• Mature B-cell (can't distinguish it from mature T-cell or B-cells based on morphology)
• Reactive lymphocyte [Compare]
• Monocyte [Compare]

› Differential Diagnoses:

If increased in blood, Lymph node or bone marrow: Infection Neoplastic (NK cell leukemia and lymphoma)

› Classic Immunophenotype:

• surface CD3- (as opposed to T-cells which are +)
• CD2+ (similar to T-cells)
• CD5- (as opposed to T-cells which are +)
• CD7+ (similar to T-cells)
• TCR- (as opposed to T-cells which are +)

› Cartoon Image:


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for direct comparison
› Misc:

• Morphologically you cannot distinguish NK cells from mature T-cells or mature B-cells