atypical lymphocyte

atypical lymphocyte

An enlarged dysmorphic lymphocyte characterised by an often irregular monocyte-like nucleus that may stretch the length of the cell, with chromatin strands that parallel the length of the nucleus; nucleoli and azurophilic granules may be present. Atypical lymphocytes are seen in various non-neoplastic conditions, classically in infectious mononucleosis (<20% of circulating WBCs are atypical), toxoplasmosis, CMV infection and viral hepatitis.

ALs were formerly (and arbitrarily) grouped into three types, now of historic interest:
• Type I—Monocyoid or prolymphocytic kidney-shaped or lobulated nuclei, with densely homogeneous hypergranular chromatin, more similar to mature lymphocytes than plasma cells; cytoplasm is bubbly, eccentric and basophilic.
• Type II—Cytoplasmic radiations from the nucleus (“ballerina skirt” cells); cells have 1+ nucleoli; chromatin is less dense and cytoplasm is less foamy than type I, contains some azurophilic granules, is basophilic, and “scallops” around RBCs.
• Type III—Nuclei are coarse, span the cell’s breadth, have clumped red-to-purple chromatin with 1–4 nucleoli; the cytoplasm is abundant, basophilic, and “scallops” around adjacent RBCs. ALs have abundant cytoplasm, with basophilic condensations where they abut RBCs; mitochondria are large, numerous and scattered throughout the cytoplasm.

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atypical lymphocyte

Downey cell Hematology An enlarged dysmorphic lymphocyte characterized by an often irregular monocyte-like nucleus which may stretch the length of the cell, with chromatin strands that parallel the length of the nucleus; nucleoli and azurophilic granules may be present; ALs are seen in various non-neoplastic conditions, classically in infectious mononucleosis, toxoplasmosis, CMV infection, and viral hepatitis. See Azurophilic granule.

McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.