CD68 explained

CD68 (Cluster of Differentiation 68) is a protein highly expressed by cells in the monocyte lineage (e.g., monocytic phagocytes, osteoclasts), by circulating macrophages, and by tissue macrophages (e.g., Kupffer cells, microglia).^[1]

Structure and function

Human CD68 is a Type I transmembrane glycoprotein, heavily glycosylated in its extracellular domain, with a molecular weight of 110 kD. Its primary sequence consists of 354 amino acids with predicted molecular weight of 37.4 kD if it were not glycosylated.^[2] The human CD68 protein is encoded by the CD68 gene which maps to chromosome 17.^[3] Other names or aliases for this gene in humans and other animals include: CD68 Molecule, CD68 Antigen, GP110, Macrosialin, Scavenger Receptor Class D, Member 1, SCARD1, and LAMP4.^{[3] [4]} The mouse equivalent is known as "macrosialin".

CD68 is functionally and evolutionarily related to other gene/protein family members, including:^{[2] [4] [5]}

• the hematopoietic mucin-like family of molecules that includes leukosialin/CD43 and stem cell antigen CD34;
• the lysosome-associated membrane glycoprotein (LAMP) family (CD68 localizes primarily to lysosomes and endosomes, but with a smaller fraction circulating to the cell surface);
• the scavenger receptor family, whose members typically function to clear cellular debris, promote phagocytosis, and mediate the recruitment and activation of macrophages.

Use in pathology and research

Immunohistochemistry can be used to identify the presence of CD68, which is found in the cytoplasmic granules of a range of different blood cells and myocytes. It is particularly useful as a marker for the various cells of the macrophage lineage, including monocytes, histiocytes, giant cells, Kupffer cells, and osteoclasts. This allows it to be used to distinguish diseases of otherwise similar appearance, such as the monocyte/macrophage and lymphoid forms of leukaemia (the latter being CD68 negative). Its presence in macrophages also makes it useful in diagnosing conditions related to proliferation or abnormality of these cells, such as malignant histiocytosis, histiocytic lymphoma, and Gaucher's disease.^{[6] [7]}

Anti-CD68 monoclonal antibodies that react with tissues of rodent and other species include ED1, FA-11, KP1 (a.k.a. C68/684), 6A326, 6F3, 12E2, 10B1909, and SPM130. Monoclonals that react with humans include, Ki-M7, PG-M1, 514H12, ABM53F5, 3F7C6, 3F7D3, Y1/82A, EPR20545, CDLA68-1, LAMP4-824.^[8]

ED1

ED1 is the most widely used monoclonal antibody clone directed against the rat CD68 protein and is used to identify macrophages, Kupffer cells, osteoclasts, monocytes, and activated microglia in rat tissues.^{[9] [10] [11]} In this species, it is expressed in most macrophage populations and thus ED1 is commonly used as a pan-macrophage marker.^[12] However, in some cell types it is detectable only when up-regulated, such as activated but not quiescent microglia, and can thus be used as a marker of inflammatory conditions and immune reactions in those instances. Commercial suppliers report that ED1 is used for detection of the CD68 protein by immunohistochemical staining, flow cytometry, and western blot methods and that in addition to rat it cross-reacts with bovine species.

The ED1 anti-CD68 antibody is not to be confused with the fibronectin extra domain ED1.^[13]

See also

• Cluster of differentiation
• Lysosome-associated membrane glycoprotein
• Scavenger receptor (immunology)

Further reading

• Human Gene Database: GeneCards CD68
• UniProt Knowledgebase (CD68_HUMAN)
• Luo C, Kallajoki M, Gross R, Mulari M, Teros T, Ylinen L, Mäkinen M, Laine J, Simell O . Cellular distribution and contribution of cyclooxygenase COX-2 to diabetogenesis in NOD mouse . Cell and Tissue Research . 310 . 2 . 169–75 . November 2002 . 12397372 . 10.1007/s00441-002-0628-6 . 8645558 .
• O'Reilly D, Quinn CM, El-Shanawany T, Gordon S, Greaves DR . Multiple Ets factors and interferon regulatory factor-4 modulate CD68 expression in a cell type-specific manner . The Journal of Biological Chemistry . 278 . 24 . 21909–19 . June 2003 . 12676954 . 10.1074/jbc.M212150200 . 26171842 . free .
• Le BH, Boyer PJ, Lewis JE, Kapadia SB . Granular cell tumor: immunohistochemical assessment of inhibin-alpha, protein gene product 9.5, S100 protein, CD68, and Ki-67 proliferative index with clinical correlation . Archives of Pathology & Laboratory Medicine . 128 . 7 . 771–5 . July 2004 . 15214825 . 10.5858/2004-128-771-GCTIAO .
• Mazur G, Haloń A, Wróbel T, Kuliczkowski K . Macrophage/histiocytic antigen CD68 expression in neoplastic and reactive lymph nodes . Roczniki Akademii Medycznej W Bialymstoku . 49 . 73–5 . 2004 . Suppl 1 . 15638380 .
• Kunz-Schughart LA, Weber A, Rehli M, Gottfried E, Brockhoff G, Krause SW, Andreesen R, Kreutz M . [The "classical" macrophage marker CD68 is strongly expressed in primary human fibroblasts] . de . Verhandlungen der Deutschen Gesellschaft für Pathologie . 87 . 215–23 . 2003 . 16888915 .
• Kim JS, Romero R, Cushenberry E, Kim YM, Erez O, Nien JK, Yoon BH, Espinoza J, Kim CJ . Distribution of CD14+ and CD68+ macrophages in the placental bed and basal plate of women with preeclampsia and preterm labor . Placenta . 28 . 5–6 . 571–6 . 2007 . 17052752 . 10.1016/j.placenta.2006.07.007 .
• O'Reilly D, Greaves DR . Cell-type-specific expression of the human CD68 gene is associated with changes in Pol II phosphorylation and short-range intrachromosomal gene looping . Genomics . 90 . 3 . 407–15 . September 2007 . 17583472 . 10.1016/j.ygeno.2007.04.010 .
• Lee CH, Espinosa I, Vrijaldenhoven S, Subramanian S, Montgomery KD, Zhu S, Marinelli RJ, Peterse JL, Poulin N, Nielsen TO, West RB, Gilks CB, van de Rijn M . Prognostic significance of macrophage infiltration in leiomyosarcomas . Clinical Cancer Research . 14 . 5 . 1423–30 . March 2008 . 18316565 . 10.1158/1078-0432.CCR-07-1712 . 10778386 . free .
• Chen WS, Chen CH, Lin KC, Tsai CY, Liao HT, Wang HB, Chen YK, Yang AH, Chen TC, Chou CT . Immunohistological features of hip synovitis in ankylosing spondylitis with advanced hip involvement . Scandinavian Journal of Rheumatology . 38 . 2 . 154–5 . 2009 . 19165649 . 10.1080/03009740802409504 . 36057425 .

Notes and References

1. Holness CL, Simmons DL . Molecular cloning of CD68, a human macrophage marker related to lysosomal glycoproteins . Blood . 81 . 6 . 1607–13 . March 1993 . 7680921 . 10.1182/blood.V81.6.1607.1607. free .
2. Web site: CD68 - Macrosialin precursor - Homo sapiens (Human) - CD68 gene & protein. www.uniprot.org. 16 September 2017. en.
3. Web site: CD68 Symbol Report. www.genenames.org. 16 September 2017.
4. Web site: CD68 Gene - CD68 Protein - CD68 Antibody. www.genecards.org. 16 September 2017.
5. Web site: MACROPHAGE ANTIGEN CD68; CD68. omim.org. 16 September 2017. en-us.
6. Book: Leong, Anthony S-Y. Cooper, Kumarason. Leong, F Joel W-M. 2003. Manual of Diagnostic Cytology. 2. Greenwich Medical Media, Ltd.. 135–136. 1-84110-100-1.
7. Manduch M, Dexter DF, Jalink DW, Vanner SJ, Hurlbut DJ . Undifferentiated pancreatic carcinoma with osteoclast-like giant cells: report of a case with osteochondroid differentiation . Pathology, Research and Practice . 205 . 5 . 353–9 . January 2009 . 19147301 . 10.1016/j.prp.2008.11.006 .
8. Web site: Product Overview: anti-CD68 Antibodies. www.antibodies-online.com. 14 September 2017. en.
9. Dijkstra CD, Döpp EA, Joling P, Kraal G . The heterogeneity of mononuclear phagocytes in lymphoid organs: distinct macrophage subpopulations in the rat recognized by monoclonal antibodies ED1, ED2 and ED3 . Immunology . 54 . 3 . 589–99 . March 1985 . 3882559 . 1453512 .
10. Gomes LF, Lorente S, Simon-Giavarotti KA, Areco KN, Araújo-Peres C, Videla LA . Tri-iodothyronine differentially induces Kupffer cell ED1/ED2 subpopulations . Molecular Aspects of Medicine . 25 . 1–2 . 183–90 . 2004 . 15051326 . 10.1016/j.mam.2004.02.018 .
11. Xie R, Kuijpers-Jagtman AM, Maltha JC . Osteoclast differentiation and recruitment during early stages of experimental tooth movement in rats . European Journal of Oral Sciences . 117 . 1 . 43–50 . February 2009 . 19196317 . 10.1111/j.1600-0722.2008.00588.x . 848129 .
12. Damoiseaux JG, Döpp EA, Calame W, Chao D, MacPherson GG, Dijkstra CD . Rat macrophage lysosomal membrane antigen recognized by monoclonal antibody ED1 . Immunology . 83 . 1 . 140–7 . September 1994 . 7821959 . 1415006 .
13. Vincent PA, Rebres RA, Lewis EP, Hurst V, Saba TM . Release of ED1 fibronectin from matrix of perfused lungs after vascular injury is independent of protein synthesis . The American Journal of Physiology . 265 . 5 Pt 1 . L485-92 . November 1993 . 8238536 . 10.1152/ajplung.1993.265.5.L485 .