CD45


CD45 is a protein found on the surface of most cells in the immune system, including white blood cells (also called leukocytes). CD45 helps these immune cells communicate and respond appropriately to infections and inflammation.

Why do pathologists test for CD45?

Pathologists test for CD45 to help determine if cells seen in a tissue sample are from the immune system. Testing for CD45 helps distinguish immune cells, including white blood cells, from other types of cells, such as epithelial cells (cells lining organs and tissues), muscle cells, or nerve cells. This distinction is important for diagnosing various conditions, especially lymphoma (cancer of immune cells).

How do pathologists test for CD45?

Pathologists test for CD45 using a technique called immunohistochemistry. This test involves applying antibodies designed to attach only to the CD45 protein on a thin slice of tissue placed on a microscope slide. A chemical reaction then causes the cells containing CD45 to change colour. Cells showing this colour change are called “positive,” indicating they have CD45 on their surface, while cells without a colour change are called “negative.”

What types of normal cells and tissues will be positive for CD45?

Normal cells positive for CD45 include nearly all immune system cells such as:

These cells naturally express CD45 because it helps them function within the immune system.

What types of tumours will be positive for CD45?

Tumours commonly positive for CD45 arise from immune cells or white blood cells.

Examples include:

  • Lymphomas, which are cancers of lymphocytes (immune system cells).

  • Leukemias, which are cancers of blood-forming cells.

  • Myeloid sarcoma, a tumour made of immature myeloid cells.

Identifying CD45 helps pathologists confirm the diagnosis of these tumours and differentiate them from other cancers that originate from non-immune cells. This information guides your doctor in choosing the best treatment for you.

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