Learning Objectives
- Identify the morphological features of a basophil in a peripheral blood smear.
- Distinguish between basophils, band neutrophils, and lymphocytes.
- Recognize the staining characteristics of coarse, dark granules.
- Understand the clinical significance of basophilia in myeloproliferative disorders.
Overview of Basophils and Companion Cells
This high-power microscopic view of normal peripheral blood demonstrates a basophil alongside a band neutrophil and a lymphocyte. Basophils are the least common type of granulocyte in a normal differential count.
Characteristic Features: The Basophil
- Granules: Characterized by large, coarse, dark purple-to-black granules that are often so numerous they obscure the nucleus.
- Nucleus: Usually bilobed or S-shaped, though difficult to see through the dense granulation.
- Contents: The granules contain histamine, heparin, and peroxidase, which are released during inflammatory and allergic responses.
Companion Cell Comparison
- Band Neutrophil: Recognizable by its C-shaped or U-shaped nucleus without distinct lobes, representing an immature stage of neutrophil development.
- Lymphocyte: A small, mononuclear cell with a dense, round nucleus and a very thin rim of pale blue cytoplasm.
Clinical Relevance: Basophilia
- Myeloproliferative Neoplasms: A significant increase in basophils (basophilia) is a highly suggestive clinical finding for Chronic Myeloid Leukemia (CML).
- Allergic Reactions: Basophils work similarly to tissue mast cells; they bind IgE and degranulate during immediate hypersensitivity reactions.
- Inflammation: While rare, basophilia can occasionally be seen in chronic inflammatory states or certain viral infections.
