CD5

September 24, 2023

CD5 is a specialized type of protein normally found on the surface of immune cells where it is involved in modulating signal transduction pathways. It plays a significant role in regulating immune responses and maintaining the balance between activating and inhibiting signals within the immune system.

What does CD5 do?

• Regulates T-cell activation: CD5 is important in regulating the activation and sensitivity of T cells to antigens. It modulates the signaling threshold for T cell activation, ensuring that the immune response is appropriately calibrated.
• B-cell differentiation: In B cells, CD5 is thought to be involved in the differentiation and regulation of a subset of B cells known as B-1 cells, which are important for producing natural antibodies.
• Immune homeostasis: It plays a role in maintaining immune homeostasis by preventing overactivation of the immune system, which could lead to autoimmune disorders.

Normal cells that express CD5

• T cells: CD5 is widely expressed on the surface of T cells, which are a central part of the adaptive immune system. T cells are found throughout the body, particularly in lymphoid tissues such as the thymus, spleen, and lymph nodes.
• B cells: A subset of B cells, known as B-1 cells, also express CD5. B-1 cells are primarily located in the peritoneal and pleural cavities, and they play a role in the innate immune response by producing natural antibodies.

Cancers that express CD5

CD5 expression is associated with several types of hematological malignancies, including:

• Chronic lymphocytic leukemia (CLL): Most cases of CLL show CD5 positivity, making it a useful marker in the diagnosis of this condition.
• Mantle cell lymphoma (MCL): MCL cells typically express CD5, which helps differentiate it from other types of non-Hodgkin lymphomas.
• T-cell lymphomas: Some types of T-cell lymphomas may express CD5, although its expression can vary among different T-cell malignancies.

Detection of CD5 in tissue samples

Common tests used to detect CD5 in a tissue sample include immunohistochemistry (IHC) and flow cytometry. While IHC provides spatial information about where CD5 is expressed within tissue samples, flow cytometry offers quantitative data on the proportion of cells expressing CD5 and the intensity of that expression, making it invaluable for diagnosing and monitoring blood cancers.

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

Other helpful resources

Atlas of pathology