CD 44

Available from Biodesign (T2.F4, BU52), Cymbus Bioscience (F10-44-2), Dako (DF1485, 2B11), Immunotech (J.173), Oncogene (A3D8, AIG3), Pharmingen (OX-49), RDI (F10-44-2), Sanbio (MEM-85), Seralab (A3D8, AIG3), Serotec (F10-44-2) and Sigma (A3D8).

CD 44v6
Available from R & D Systems (2F10) and various isoforms including v4, v5, v6, v7 and v7-v8 are available from Bender MedS.

The antibodies, particularly CA1G3, are effective in formalin-fixed, paraffin-embedded tissues but staining is optimal only after microwave-induced epitope retrieval in 10 mM citrate buffer at pH 6.0. Enzyme digestion should not be performed as this has been shown to alter the integrity of the antigen.

The CD 44 receptor is also known as phagocytic glycoprotein (Pgp-1), extracellular matrix receptor III (ECM-III), B cell p80 antigen, lymphocyte homing receptor (Hermes antigen) and hyaluronate cellular adhesion molecule (H-CAM). CD 44 shows considerable homology with the cartilage link proteins involved in adhesion between hyaluronate and other proteoglycans in the extracellular matrix including collagen, fibronectin and ankyrin. Besides this function, CD 44 has since been found to have a role in recognition between lymphocytes and endothelial cells and in lymphocyte homing to the reticuloendothelial tissues. This latter function has led to interest in its possible role in the regulation of tumor cell dissemination.
The CD 44 family of glycoproteins exists in a number of variant isoforms, the most common being the standard 85-95kD or hematopoietic variant (CD 44s) found in mesodermal cells such as hematopoietic, fibroblastic and glial cells and in some carcinoma cell lines. The receptor is coded in five distinct domains located on the short arm of chromosome 11. The heterogeneity in the CD 44 molecule results from posttranslational modification of the protein and alternative splicing of up to ten exons results in variant isoforms of higher molecular mass (140-160 kD) which may be expressed individually or in various combinations, with potentially diverse functions. Higher molecular weight isoforms have been described in epithelial cells (CD 44v) and are thought to function in intercellular adhesion and stromal binding. While the other functions and distributions of the CD 44 family have not yet been completely elucidated, they are also known to participate in embryonic development and angiogenesis as well as other molecular processes associated with specific adhesions, signal transduction and cell migration. The recent demonstration of a concordance of the cell proliferation nuclear antigen Ki-67 and CD 44 expression in adenomatous polyps, colonic carcinomas and adjacent mucosa raises the possibility of CD 44 involvement in stimulating cell growth (Abassi et al, 1993).
Following the discovery that the splice variants, especially exon v4-7, initiated the lymphatic spread of rat pancreatic carcinoma cells, the role of the highly interspecies-conserved CD 44 in human tumor progression and metastasis has been examined. It appears that the CD 44-hyaluronate interaction is central to tumor invasiveness, the receptor allowing the uptake and subsequent degradation of matrical hyaluronate. While many human tumors express CD 44, a positive correlation between increased CD 44v expression and tumor progression and/or dedifferentiation has been demonstrated in only some (East & Hart, 1993). Such tumors include non-Hodgkin's lymphoma (Stauder et al, 1995), hepatocellular carcinoma (Mathew et al, 1996), breast carcinoma, renal cell carcinoma (Terpe et al, 1993), colonic carcinoma (Abassi et al, 1993; Wielenga et al, 1993; Herrlich et al, 1995) and some soft tissue tumors (Wang et al, 1996). Conversely, CD 44v expression is downgraded in other tumors including neuroblastoma (Shtivelman & Bishop, 1991), squamous cell and basal cell carcinomas of the skin
(Herold-Mende et al, 1996).

The suggestion that there is a positive association between CD 44 isoform expression and progression in human tumors has important implications for diagnosis and prognosis. Unfortunately, the situation is not yet clearcut. Confusion over the complicated exon boundaries and the different nomenclature employed by researchers have added to problems of identifying the true metastasis-associated isoform. Furthermore, stromal cells may contribute to the isoform pattern detected. For example, activated lymphocytes may express the so-called metastasis-associated variant of CD 44, emphasizing the importance of immunohistological assessment as a method that allows morphologic discrimination.

Currently, applications of CD 44 still lie in the research domain. While antibodies to specific isoforms are available, some reactive in fixed paraffin-embedded tissues, the antibody to pan-CD 44 molecule has been the most widely used in paraffin sections. Microwave epitope retrieval is essential for the demonstration of the antigen. While CD 44 is a plasmalemmal determinant, both cytoplasmic and cell membrane-staining patterns have been demonstrated in non-neoplastic and neoplastic cells. It has been suggested that exclusive cytoplasmic staining may reflect the overproduction of the protein so that not all of it can be incorporated into the cell membrane. Alternatively, the production of aberrant forms or massive shedding of the CD 44 molecule from the cell membrane could account for this pattern of staining.

•Abassi AM, Chester KA, Talbot IC et al 1993. CD 44 is associated with proliferation in normal and neoplastic human colorectal epithelial cells. European Journal of Cancer 29A:294.

•East JE, Hart IR 1993. CD 44 and its role in tumor progression and metastasis. European Journal of Cancer 29:1921-1922.

•Herold-Mende C, Seiter S, Born AI et al 1996. Expression of CD 44 splice variants in squamous epithelia and squamous cell carcinomas of the head and neck. Journal of Pathology 179:66-73.

•Herrlich P, Pals S, Ponta H 1995. CD 44 in colon cancer. European Journal of Cancer 31:1110-12.

•Mathew J, Hines JE, Obafunwa JO et al 1996. CD 44 is expressed in hepatocellular carcinomas showing vascular invasion. Journal of Pathology 179:74-79.

•Shtivelman E, Bishop JM 1991. Expression of CD 44 is repressed in neuroblastoma cells. Molecular and Cell Biology 11:5446-5453.

•Stauder R, Eisterer W, Thaler J, Gunther U 1995. CD 44 variant isoforms in non-Hodgkin's lymphoma: a new independent prognostic variable. Blood 85: 885-2899.

•Terpe HJ, Tajrobehkar K, Gunthert U, Altmannsberger M 1993. Expression of cell adhesion molecules alpha-2, alpha-5 and alpha-6 integrin, E-cadherin, NCAM and CD 44 in renal cell carcinoma: an immunohistochemical study. Virchow's Archives 422:219-24.

•Wang HH, DeYoung BR, Swanson PE, Wick MR 1996. CD 44 immunoreactivity in soft tissue sarcomas. Applied Immunohistochemistry 4: 184-189.

•Wielenga VJM, Heider K-H, Offerhaus GJA et al 1993. Expression of CD 44 variant proteins in human colorectal cancer is related to tumour progression. Cancer Research 53: 4754-4756.

Manual of diagnostic antibodies for immunohistology / Anthony S.-Y. Leong, Kumarasen Cooper, F. Joel W.-M. Leong.