CD45

Assessments
Characteristics
CD45 is a family of single chain transmembrane glycoproteins, 180-235 kDa, consisting of at least four isoforms which share a common large intracellular domain. Their extracellular domains are rod shaped, heavily glycosylated. The different isoforms are produced by alternative messenger RNA splicing of three exons of a single gene on chromosome 1q31-32. CD45 is expressed on cells of the human haematopoietic lineage with the exception of mature red cells. It is not detected on differentiated cells of other tissues. CD45 has intrinsic tyrosine phosphatase activity with essential for development and effector functions, playing an important role in signal transduction, inhibition or upregulation of various immunological functions. CD45 is exclusively expressed in haematolymphoid cells. Almost all haematolymphoid cells, including precursor cells and mature B- and T-lymphocytes, granulocytes, monocytes/histiocytes and interdigitating reticulum cells and follicular dendritic cells express CD45. While CD45 is strongly expressed on the lymphocyte membranes, histiocytes only exhibit a weak membrane staining. CD45 is lost in maturing erythocytes, megakaryocytes and plasma cells. The extracellular isoforms are designated ABC, AB, BC, B and O. B-lymphocytes express the high molecular weight CD45 isoform of 220 kDa, which include the isoform ABC. T-lymphocytes can express multiple isoforms. Histiocytes and granulocytes mainly express the B and O. CD45 proteins that do not comprise all of the isoforms are designated CD45R (=restricted).
Neoplasms
CD45 is detected in the large majority of haematolymphoid neoplasms, i.e., leukaemias and malignant lymphomas. 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.
Application
CD45 is an important marker in the primary tumour screening panel in order to identify haematolymphoid differentiation. Loss of CD45 in precursor B-cell neoplasms is a negative prognostic parameter.
Controls
In tonsil all B- and T-cells must show strong and distinct membranous staining reaction, while Kupffer cells in liver or microglia in brain tissue must show an at least weak to moderate but distinct staining reaction. No staining should be seen in the squamous epithelial cells and hepatocytes.
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.
10.04.13 - MV/LE