Image MCQs: Downey Cells

Atypical lymphocytes or Downey cells are lymphocytes that become large as a result of antigen stimulation.

The nucleus of a reactive lymphocyte can be round, elliptic, indented, cleft or folded and may contain nucleolus. The cytoplasm is often abundant and can be basophilic. Vacuoles and/or azurophilic granules are also sometimes present.

The distinctive cell associated with EBV or CMV is known as a "Downey cell", after Hal Downey, who contributed to the characterization of it in 1923. It is sometimes called a "Downy cell".

The WBC's seen here are "atypical" lymphocytes. They are atypical because they are larger (more cytoplasm) and have nucleoli in their nuclei. The cytoplasm tends to be indented by surrounding RBC's. Such atypical lymphocytes are often associated with infectious mononucleosis.

These cells are most commonly seen in EBV infections but may also be seen in CMV, Toxoplasmosis and some other viral infections.

More related info:

Disease Mechanisms of Epstein-Barr Virus (EBV)

Virus in saliva initiates infection of oral epithelia and tonsillar B cells.
There is productive infection of epithelial and B cells.
Virus promotes growth of B cells (immortalizes).
T cells kill and limit B-cell outgrowth. T cells are required for controlling infection. Antibody role is limited.
EBV establishes latency in memory B cells and is reactivated when the B cell is activated.
T-cell response (lymphocytosis) contributes to symptoms of infectious mononucleosis.
There is causative association with lymphoma in immunosuppressed people and African children living in malarial regions (African Burkitt lymphoma) and with nasopharyngeal carcinoma in China.