Mature T-cells

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Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Lymphoid ›› T-cells ›› Normal

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›Microscopic Features:

Slightly (~1.5x) larger than a mature RBC
High nuclear to cytoplasmic ratio but with
Round mature Nucleus (clumped chromatin)
Nucleoli are absent
Cytoplasm is scant, light blue and lacks granules

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

PB: 2nd most common nucleated cell (WBC) in blood and most common lymphocyte in blood
BM: Scattered (<10%)
LN: Mainly scattered in Interfollicular areas of lymphoid tissue

›May Resemble:

Mature B-cells (can't distinguish T-cell and B-cell based on morphology)
Orthochromic normoblast
Plasma cell (mature)
Reactive lymphocyte
Monocyte

›Differential Diagnoses:

If increased in blood, Lymph node or bone marrow:
Infection
Neoplastic (mature T-cell lymphoma or leukemia)
Drug-induced
Autoimmune disorders
Idiopathic

›Classic Immunophenotype:

CD2+
CD3+
CD4+ or CD8+
CD5+
CD7+
TCR+
TdT-
CD34-

›Cartoon Image:

Click and drag Red blood cell for scale

for direct comparison

›Misc:

Morphologically you cannot distinguish mature T-cells from mature B-cells
In blood: There are more CD4+ T-cells than CD8+ T-cells (CD4:CD8 ratio is ~2-3:1)
Majority of the mature T-cells express the Alpha/Beta TCR (only a small minority express the Gamma/Delta TCR)