Which cell surface markers define helper T cells (CD4+) and cytotoxic T cells (CD8+) in flow cytometry?

Which cell surface markers define helper T cells (CD4+) and cytotoxic T cells (CD8+) in flow cytometry?

• A. CD3 marks helper T cells; CD19 marks cytotoxic T cells.
• B. CD4 marks helper T cells; CD8 marks cytotoxic T cells.
• C. CD8 marks helper T cells; CD4 marks cytotoxic T cells.
• D. CD19 marks helper T cells; CD3 marks cytotoxic T cells.

Answer: (B)

In flow cytometry analyses of T cells, specific surface proteins define the two main subsets. Helper T cells express CD4 on their surface, while cytotoxic T cells express CD8. This allows you to distinguish the two populations by staining for CD4 and CD8 and identifying CD4-positive cells as helpers and CD8-positive cells as cytotoxic. CD3 is a marker that is present on most mature T cells, so it’s useful for selecting T cells in general, not for telling them apart. CD19 marks B cells, not T cells, so it’s not used to define helper versus cytotoxic T cells. In practice, you’d gate on CD3-positive T cells and then separate them into CD4-positive (helper) and CD8-positive (cytotoxic) subsets.

In flow cytometry analyses of T cells, specific surface proteins define the two main subsets. Helper T cells express CD4 on their surface, while cytotoxic T cells express CD8. This allows you to distinguish the two populations by staining for CD4 and CD8 and identifying CD4-positive cells as helpers and CD8-positive cells as cytotoxic. CD3 is a marker that is present on most mature T cells, so it’s useful for selecting T cells in general, not for telling them apart. CD19 marks B cells, not T cells, so it’s not used to define helper versus cytotoxic T cells. In practice, you’d gate on CD3-positive T cells and then separate them into CD4-positive (helper) and CD8-positive (cytotoxic) subsets.