Cluster of Differentiation (CD) Antigens  Go back
Leukocytes express distinct assortments of molecules on their cell surfaces, many of which reflect either different stages of their lineage-specific differentiation or different states of activation or inactivation. Leukocyte cell surface molecules are routinely detected with anti-leukocyte monoclonal antibodies (mAbs). Using different combinations of mAbs, it is possible to chart the cell surface immunophenotypes of different leukocyte subpopulations, including the functionally distinct mature lymphocyte subpopulations of B-cells, helper T-cells (TH), cytotoxic T-cells (TC), and natural killer (NK) cells.
The abbreviations used for identifying different leukocyte cell surface molecules are somewhat complex because historically three conventions have been used:
Conventions for Naming Leukocyte Surface Molecules
  1. By one convention, cell surface molecules are named according to a particular function affected by an anti-leukocyte mAb. For example, the lymphocyte function-associated antigen 1, or LFA-1, was so named because antibodies recognizing this structure interfere with lymphocyte cell adhesion events and optimal lymphocyte function.
  2. The second convention is effectively no convention at all. Molecules are named arbitrarily according to individual laboratory preferences. For example, no obvious logic follows in the designations B7 and B220, except that the leading "B" reminds us that these antigens are typically expressed on B lymphocytes.
  3. By a third convention, leukocyte cell surface molecules are named systematically by assigning them a cluster of differentiation (CD) antigen number that includes any antibody having an identical and unique reactivity pattern with different leukocyte populations.
Although less intuitive, the CD antigen convention has become the accepted norm for formal designation of leukocyte surface molecules. This is a logical consequence of the fact that most leukocyte cell surface molecules were discovered only by their reactivity patterns with anti-leukocyte antibodies when little, if anything, was known about their functions. Also, because most leukocyte cell surface molecules are recognized by more than one antibody, it is easy to group antibodies according to identical reactivity patterns even though they may recognize different portions of the same molecule. An obvious problem, though, is that some antibodies recognize more than one distinct leukocyte surface structure as is the case, for example, with the structurally heterogeneous CD45 splice variants. Different variants have identical protein domains, and anti-CD45 antibodies recognizing these shared domains will cross-react with more than one CD45 variant.

A few hundred human cell surface molecules have so far been assigned CD antigen designations. Note that some CD antigens have also been named by one of the other conventions.

For example: Some CD antigens are widely expressed on different leukocyte populations while others are expressed on only one type or just a few types of leukocytes. For example:
Commercial listings of anti-CD monoclonal antibodies are easy to find on the web.
Cells & Organs of the Immune System
Blood Cell Morphology & Staining
© Duane W. Sears
29 August, 2009