Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Normal Mature T-cells* Click Here for Full Size › 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 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)