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n. 1 (context electronics English) a 120-mm (5-inch) CD (compact disc) 2 (context music English) a 5-inch CD single


CD5 or CD-5 may be:

  • CD5 (protein), cluster of differentiation 5 molecule, type I transmembrane protein
  • Compact disc, 5-inch CD, usually music CD
    • CD single, a music single on a 5-inch CD
CD5 (protein)

CD5 is a cluster of differentiation , and also on T cells. B-1 cells have limited diversity of their B-cell receptor due to their lack of the enzyme terminal deoxynucleotidyl transferase (TdT) and are potentially self-reactive. CD5 serves to mitigate activating signals from the BCR so that the B-1 cells can only be activated by very strong stimuli (such as bacterial proteins) and not by normal tissue proteins. CD5 was used as a T-cell marker until monoclonal antibodies against CD3 were developed.

In humans, the gene is located on the long arm of chromosome 11. There is no confirmed ligand for CD5 but there is evidence that CD72, a C-type lectin, may be a ligand or that CD5 may be homophilic, binding CD5 on the surface of other cells.

T cells express higher levels of CD5 than B cells. CD5 is upregulated on T cells upon strong activation. In the thymus, there is a correlation with CD5 expression and strength of the interaction of the T cell towards self-peptides.