CD5

CD5 is a protein normally found on the surface of specific immune cells, particularly certain types of lymphocytes (a kind of white blood cell). CD5 helps these immune cells communicate and interact within the immune system, especially in regulating immune responses and preventing autoimmune reactions.

Why do pathologists test for CD5?

Pathologists test for CD5 to help determine if specific immune cells are present in a tissue sample. Testing for CD5 can help identify particular types of cancers, especially certain lymphomas (cancers involving lymphocytes), and distinguish them from other lymphomas and related conditions.

How do pathologists test for CD5?

Pathologists test for CD5 using immunohistochemistry. This method involves applying antibodies designed to attach specifically to CD5 proteins present on cells in a thin slice of tissue placed on a microscope slide. A chemical reaction then makes cells containing CD5 change colour. Cells showing this colour change are called “positive,” meaning they express CD5, while cells without the colour change are called “negative.”

What types of normal cells and tissues will be positive for CD5?

Normal cells positive for CD5 include:

• T lymphocytes (T cells), a key type of immune cell involved in protecting the body from infection.

• A small subset of B lymphocytes (B cells), another type of immune cell important in antibody production.

CD5 is normally expressed by these cells as part of their natural function within the immune system.

What types of tumors will be positive for CD5?

Several types of tumours are typically positive for CD5, including:

• Chronic lymphocytic leukemia (CLL): Chronic lymphocytic leukemia is a cancer involving mature B lymphocytes commonly expressing CD5.

• Mantle cell lymphoma (MCL): Mantle cell lymphoma is an aggressive type of lymphoma originating from B cells that express CD5.

• T cell lymphomas: A group of cancers arising from T cells, which generally express CD5 as part of their normal identity.

Identifying CD5 in these tumours helps pathologists accurately diagnose and distinguish these cancers from similar types of lymphomas that do not express CD5. This precise diagnosis assists your doctor in selecting the most effective treatment.