Hi, lotusbud.
There are more than 250 types of CD (cluster of differentiation) molecules on the surfaces of cells in our bodies. Because they are useful for classifying white blood cells, they are used in diagnosing lymphoma, leukemia, and MDS, each which involve WBCs.
You can find general information and links to specific information about certain common markers at
http://en.wikipedia.org/wiki/Cluster_of_differentiation
Technical details about specific markers can also be found at
http://www.pathologyoutlines.com/cdmarkers.html
Hope this helps,
Ruth