CD45, also known as Protein tyrosin phosphatase, receptor C (PTPRC), and leucocyte common antigen (LCA), is a transmembrane glycoprotein with at least six human isoforms. They share a common intracellular domain and have heavily glycosylated extracellular domains. The isoforms are produced by alternative mRNA splicing of three exons (exon 4-6). CD45 has intrinsic tyrosine phosphatase activity, playing an important role in signal transduction, inhibition or upregulation of various immunological functions. The gene is located on chromosome 1q31-32. 

CD45 is expressed exclusively on cells of hematopoietic lineage with the exception of mature red cells. It is not detected on differentiated cells of other tissues. Almost all heematolymphoid cells, including precursor cells and mature B- and T-lymphocytes, granulocytes, monocytes/histiocytes and interdigitating reticulum cells and follicular dendritic cells express CD45. 

The isoforms are designated RABC, RAB, RBC, RB, RA and RO and are expressed on different subsets of hematopoietic cells. 


CD45 is detected in the large majority of hematolymphoid neoplasms. Overall, about 90% of malignant lymphomas are CD45 positive. The proportion is lower among precursor B-cell neoplasms (80% of B-ALL) and large cell anaplastic lymphomas, and only about 10% of plasmacytic neoplasms are positive. In Hodgkin lymphoma, the L&H cells in the LP-type are always positive, while Reed-Sternberg cells in classic Hodgkin lymphoma are negative or only show a faint cytoplasmic staining. CD45 is also detected in virtually all cases of mast cell neoplasms, and true histiocytic and dendritic cell neoplasms, with the possible exception of fibroblastic variants.


CD45 is an important marker in the primary tumour screening panel in order to identify hematolymphoid differentiation.


Tonsil and liver are recommendable as positive and negative tissue controls. In tonsil, all lymphocytes (B- and T-cells) and histiocytes must display a strong distinct membranous staining reaction. Squamous epithelial cells should be negative. In liver, the Kupffer cells should show a weak to moderate staining reaction whereas hepatocytes must be negative. Scattered lymphocytes can be seen in the liver and must display strong, distinct membranous staining reaction.

Selected references

Dahlke MH, Larsen SR, Rasko JE, Schlitt HJ. The biology of CD45 and its use as a therapeutic target. Leuk Lymphoma. 2004 Feb;45(2):229-36. Dunphy CH, Gardner LJ, Manes JL, Bee CS, Taysi K. CD30+ anaplastic large-cell lymphoma with aberrant expression of CD13: case report and review of the literature. J Clin Lab Anal. 2000;14(6):299-304. Gaertner EM, Tsokos M, Derringer GA, Neuhauser TS, Arciero C, Andriko JA. Interdigitating dendritic cell sarcoma. A report of four cases and review of the literature. Am J Clin Pathol. 2001 Apr;115(4):589-97. Maitra A, McKenna RW, Weinberg AG, Schneider NR, Kroft SH. Precursor B-cell lymphoblastic lymphoma. A study of nine cases lacking blood and bone marrow involvement and review of the literature. Am J Clin Pathol. 2001 Jun;115(6):868-75. Penninger JM, Irie-Sasaki J, Sasaki T, Oliveira-dos-Santos AJ. CD45: new jobs for an old acquaintance. Nat Immunol. 2001 May;2(5):389-96. Tchilian EZ, Beverley PC. CD45 in memory and disease. Arch Immunol Ther Exp (Warsz). 2002;50(2):85-93.

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