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Blood Film




  • Lymphocytes tend to be small leukocytes with a large nucleus, though may be larger with a lower nuclear:cytoplasmic ratio if reactive. These cells play several key roles in the adaptive immune response.
    • Normal Lymphocytes

    • Small lymphocyte (B cell, T cell): small cells with a large nucleus and thin cytoplasm
    • Large granular lymphocyte (cytotoxic T cell, NK cell): larger cells with a low nuclear : cytoplasmic ratio and cytoplasmic granules


  • Increased circulating lymphocytes.
    • Lymphocytosis
    • Causes of Lymphocytosis

    • Relative Lymphocytosis

    • Acute viral infection
    • Autoimmune disease
    • Thyrotoxicosis
    • Adrenocortical insufficiency
    • Hyposplenism
    • Absolute Lymphocytosis

    • Acute viral infection - EBV, CMV, viral hepatitis
    • Chronic infection - TB, brucellosis
    • Chronic lymphocytic leukaemia


  • Reduced circulating lymphocytes.
    • Causes of Lymphopaenia

    • Primary immunodeficiency disorders - e.g. severe combined immunodeficiency, Wiskott-Aldrich syndrome
    • Infection - viral (especially HIV), bacterial, TB, malaria, fungal
    • Medications - corticosteroids, cytotoxic chemotherapy, methotrexate, azathioprine, rituximab
    • Dietary deficiency - severe malnutrition, alcohol abuse, zinc deficiency
    • Autoimmune disease (especially SLE)
    • Sarcoidosis
    • Hodgkin lymphoma
    • Aplastic anaemia
    • Radiotherapy
    • Post surgery

Atypical Lymphocytes

  • There are many different types of atypical lymphocytes of varied morphology, though they tend to be identified as reactive or neoplastic in nature. These may be difficult to distinguish on morphological examination.
    • Atypical Lymphocyte Findings

    • Larger cell size
    • Irregular cell outline
    • Immature (less condensed) chromatin
    • Nucleoli
    • Basophilic cytoplasm
    • Types of Atypical Lymphocytes

    • Reactive lymphocytesEBV, CMV, HIV, toxoplasmosis, bordatella pertussis
    • Plasmacytoid lymphocytes (Türk cells) - small to medium lymphocytes with a deep blue cytoplasmReactive - the intermediate stage between a B cell and plasma cell
    • Neoplastic lymphocytesAcute lymphoblastic leukaemia, chronic lymphocytic anaemia, leukaemic phase of non-Hodgkin lymphoma
    • Examples

    • A reactive lymphocyte in a patient with acute mononucleosis.
    • A reactive lymphocyte in a patient with acute mononucleosis.
    • A plasmacytoid lymphocyte (Türk cell).
    • A plasmacytoid lymphocyte (Türk cell).

Circulating Plasma Cells

  • Plasma cells are specialised immune cells derived from B cells which secrete antibodies. They are not usually seen within the peripheral blood except in severe infection and plasma cell dyscrasias.
  • Morphologically they are medium-to-large cells with a deep blue cytoplasm and a perinuclear 'hof' (area of pallor adjacent to the nucleus representing the golgi zone).
    • Causes of Circulating Plasma Cells

    • Severe infection / inflammation / malignancy
    • Plasma cell myeloma
    • Plasma cell leukaemia
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