CD45

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protein tyrosine phosphatase, receptor type, C
Identifiers
Symbol	PTPRC CD45
HUGO	9666
Entrez	5788
OMIM	151460
RefSeq	NM_080923
UniProt	P08575
Other data
Locus	Chr. 1 q31-q32

In immunology, the CD45 antigen (CD stands for cluster of differentiation) is a protein which was originally called leucocyte common antigen.

It is a type I transmembrane protein which is in various forms present on all differentiated hematopoietic cells except erythrocytes that assists in the activation of those cells (a form of co-stimulation).

It is expressed in lymphomas, B-cell chronic lymphocytic leukemia, hairy cell leukemia, and acute nonlymphocytic leukemia.

The CD45 family consists of multiple members that are all products of a single complex gene. This gene contains 34 exons and the primary transcripts are alternatively spliced to generate up to eight different mature mRNAs and after translation eight different protein products.

Isoforms of CD45 exist:

• on B lymphocytes, where the protein is called B220 (its molecular mass is 220 kDa) (this is true in mice, but there is not a B cell-specific isoform of CD45 known in humans)
• on naive T lymphocytes, where it is called CD45RA
• on activated and memory T lymphocytes, where it is called CD45RO

The cytoplasmic domain of CD45 is one of the largest known and it has an intrinsic phophorylase activitiy that removes an inhibitory phosphate group on a tyrosine kinase called Lck (in T cells) or Syk (in B cells) and activates it.