What does the acronym CD stand for in immunology?

• A. Clusters of differentiation
• B. Cytokines differentiation
• C. Cell determinants
• D. Co-stimulatory domains

Answer: (A)

CD stands for clusters of differentiation. This naming comes from identifying immune cell surface proteins with panels of monoclonal antibodies and grouping them into clusters that help define cell types and stages of differentiation. These CD markers are used to immunophenotype cells—for example, CD4 marks helper T cells and CD8 marks cytotoxic T cells—often by flow cytometry in clinical and research settings. The other terms don’t describe this naming convention: cytokines are signaling molecules, not a labeling system; “cell determinants” isn’t a standard term for this context; and co-stimulatory domains refer to parts of receptors involved in signaling, not the CD naming scheme.