What are Downey Cells?
Downey cells are atypical lymphocytes, also known as reactive lymphocytes or variant lymphocytes. They are a type of cytotoxic (CD8+) lymphocyte that undergoes changes in appearance in response to infection, most notably during infectious mononucleosis (IM), caused by the Epstein-Barr virus (EBV). These changes are easily identifiable under a microscope.
Several characteristics distinguish Downey cells from normal lymphocytes:
- Morphology: Downey cells are larger than typical lymphocytes and have distinctive nuclear morphology. Their nuclei are often indented or bean-shaped.
- Cytoplasm: They possess reduced cytoplasm compared to normal lymphocytes, sometimes containing azurophilic granules and vacuoles.
- Types: There are different types of Downey cells; Type I cells are slightly larger than normal lymphocytes with indented nuclei, while Type II cells are the most common type. Differences in size, nuclear shape, and cytoplasmic inclusions help categorize them.
Two major types of Downey cells exist, with variations in size and nuclear shape.
- Downey type I cells: These are slightly larger than normal lymphocytes, possessing indented or bean-shaped nuclei and reduced cytoplasm which may contain a few azurophilic granules and vacuoles.
- Downey type II cells: These cells are the most common type and are distinguished by their morphological features, though specific characteristics are not consistently detailed across all sources.
The presence of Downey cells in a blood smear can be a significant indicator of infectious mononucleosis, although it's not the sole diagnostic criterion. A complete blood count with a manual differential is a quick way to potentially identify these cells and contribute to a diagnosis. However, a definitive diagnosis typically involves considering multiple factors beyond the mere presence of these cells.
The observation of Downey cells in a blood smear often involves a manual differential count by a trained hematologist or laboratory technician. Automated methods for detecting and classifying these cells are currently under development.
