CD Nomenclature

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CD antigens are cell-surface molecules expressed on leukocytes and other cells relevant for the immune system. CD nomenclature has been universally adopted by the scientific community, it provides a unified designation system for monoclonal antibodies (mAbs), as well as for the cell-surface molecules they recognize.

A non-descriptive cluster of differentiation number (CD followed by a number) is assigned to a group or cluster of mAbs that recognize the same cell surface molecule (e.g. CD2 or CD3). The CD designation refers to a group of mAbs shown by the statistical method of cluster analysis to recognize a particular cellular differentiation pattern. The CD nomenclature is also used to name the molecule itself. For example, CD4 designates both the group of mAbs recognizing the CD4 cell surface molecule as well as the CD4 molecule itself.

A lowercase “w” preceding the number designation stands for “workshop” (e.g., CDw12), and indicates that the CD designation is tentative; it denotes an insufficiently characterized antibody or molecule. In some cases, it corresponds to a molecule defined by only one antibody submitted to the HLDA workshops.

In other cases, lowercase letters have been used to name different members of the same gene family, as is the case with CD66. With regard to carbohydrate CD structures, a lower case suffix represents a modification of the same carbohydrate sequence, e.g. for CD15.

Uppercase letters following a CD number designate a spliced variant of the extracellular domain of a cell surface molecule. For example, CD45RA or CD45RO corresponds to splice variants of CD45. A lowercase letter following the CD number (e.g., CD1a, CD1b, CD1c, CD1d or CD1e) indicates several molecules that share a common chain.

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