A good brief discussion of the CD system is given in Current
Protocols in Immunology, section A.4.1. CD stands for
"cluster of differentiation" (though Eugene Butcher says
it stands for "Completely Dull") and refers to a cluster of
antibodies against human cells that display the same
cellular reactivity and identify the same molecular species.
The example they give is CD2: "...CD2 antibodies are
monoclonal antibodies that react with a 50-kDa transmembrane
glycoprotein expressed on resting human T cells."
A similar standardized nomenclature was devised for
mouse lymphocyte antigens, the "Ly" system (Morse et al.,
Immunogenetics 25:71-78 (1987). Some people used the "Ly"
system, some used it with the analogous "CD" markers in
parentheses (e.g. Matheson and Sharrow, in Differentiation
Antigens in Lymphohemopoietic Tissues, 1988) and some used
the CD nomenclature exclusively. Now the CD system is used
for mice, replacing the Ly system (Morse, J. Immunol.
149:3129 1992). Presumably it could be used for any species
that has homologous molecules on cells of similar function.
However, Paul Kincade and Jeffrey Gimble have warned that
"Some antigens are structurally similar in many species, but
the cellular representation, or timing of acquisition of
these markers on lymphocytes, can be quite different."
Jack Komisar
