Tissue-specific and growth-regulated expression of CD44 variable exon determinants in the mouse

CD44 variant DNA vaccination with virtual lymph node ameliorates experimental autoimmune encephalomyelitis through the induction of apoptosis

Standard CD44 (CD44s) and its alternatively spliced variants (CD44v) were found to be associated with the metastatic potential of tumor cells, and with cell migration of autoimmune inflammatory cells, including cells involved in experimental autoimmune encephalomyelitis (EAE). The aim of the present study was to evaluate whether induction of anti-CD44 immune reactivity, through cDNA vaccination could down-regulate EAE. Our vaccination technique involved the insertion of CD44s or CD44v cDNA into a silicone tube filled with 2.5 cm long segment of hydroxylated-polyvinyl acetate wound dressing sponge (forming a virtual lymph node) which was implanted under the skin of SJL/J mice immunized with myelin antigens for EAE induction. Animals vaccinated with CD44v cDNA developed significantly less severe EAE when compared with sham vaccinated animals or animals vaccinated with CD44s cDNA. The in vitro proliferation of lymphocytes was preserved regarding myelin antigens and mitogens. Histopathological examinations revealed a significant reduction of EAE lesions and enhanced apoptosis in central nervous system (CNS)-infiltrating cells of the successfully vaccinated animals. Such methods of cDNA vaccination with CD44 could be applicable in inflammatory CNS diseases, like multiple sclerosis.

Monoclonal antibodies to CD44 epitopes on mouse endothelium

CD44 is a widely expressed, plasma membrane protein. Many molecular forms of CD44 are possible as it is encoded by a gene with multiple exons that can be alternatively spliced and its deduced protein sequence contains numerous glycosylation sites. Through its role as an adhesion molecule, CD44 is involved in many and diverse biological processes, including angiogenesis, lymphogenesis, wound healing, inflammation, and cancer metastasis. We have developed a new panel of rat monoclonal antibodies (MAbs) to murine CD44 by immunization with mouse lung endothelial cells (LEII cells). The antibodies were characterized using immunoprecipitation, mass spectrometry, competition binding, and cross Western blot experiments with MAb 133-13A, which recognizes CD44 expressed on tumor cells. The new MAbs recognize three distinct epitope groups. MAbs 531-2A and 531-32A compete for binding with the MAb 133-13A that was described previously. MAb 531-30A identifies a CD44 epitope found on low molecular weight forms expressed in vivo, while MAb 531-22A appears to recognize an epitope specific for endothelial cells. This novel panel of anti-CD44 antibodies has potential for investigating the role of CD44 in disease pathogenesis models in the mouse. They may be particularly useful for examining the role of endothelial cells in these models.

Heterogeneity of CD44 expression among human B-cell subpopulations

CD44 is a widely distributed cell surface glycoprotein that participates in a number of cellular adhesion and signal transduction processes. Germinal center B cells express very low levels of CD44, whereas their precursors and differentiation products express much higher levels. In immunofluorescence studies comparing 20 antibodies classified as being against the hematopoietic isoform of CD44, one antibody, A1G3, was unreactive with germinal center B cells, whereas the other antibodies showed low intensity but definite reactivity. Western blotting and sequential immunoprecipitation studies of lysates from density-separated lymphocyte fractions showed two bands that were differentially expressed and reacted differently with A1G3 compared with the other CD44 antibodies. These results suggest that germinal center B cells and non-germinal center B cells express different forms of CD44. Of 21 malignant B-cell populations examined, 5 showed reactivity with a "standard" CD44 reagent and significantly reduced reactivity with A1G3, while one sample showed the opposite pattern and the remainder were positive for both reagents. Of 10 cell lines studied, 5 were differentially stained by A1G3 and a standard CD44 antibody. PCR amplification of reverse transcribed mRNA from sorted human tonsil B-cell subpopulations and Southern blotting showed that B cells express a number of splice isoforms of CD44. These results demonstrate that B cells express multiple forms of CD44; both splice insert isoforms and variants distinguished by A1G3; the form of CD44 expressed depends on B-cell differentiation state.

CD44 isoform expression in periodontal tissues: cell-type specific regulation of alternative splicing

CD44 functions as a receptor for various extracellular matrices and plays crucial roles in homotypic and heterotypic cell-cell interactions. Recently, the molecular structure of CD44 has been extensively analyzed and multiple isoforms produced by alternative splicing of messenger RNA have been identified. In this study, we examined the expression of CD44 isoforms on different cell types isolated from periodontal tissue. In order to examine tissue differences in CD44 isoform expression, we established in vitro cell culture of human gingival fibroblasts (HGF), human periodontal ligament cells (HPDL) and human gingival epithelial cells (HGEC). These cells all expressed CD44 protein and messenger RNA. However, immunoprecipitation and Northern blot analysis revealed that HGEC expressed larger CD44 isoforms than HGF and HPDL. Reverse transcription-polymerase chain reaction with primers flanking the insertion site of alternatively spliced exons was used to study details of the heterogeneity. All cells examined expressed a major band in the absence of alternatively spliced exons and additional larger bands. In particular, HGEC contained more abundant high molecular mass species. In vitro stimulation by IL-1 beta, TNF alpha or phorbol 12-myristate 13-acetate induced an increase in total CD44 messenger RNA in HGF but not change in overall patterns of CD44 isoform expression. However, the isoform expression of HGEC was sensitive to cell density. The amount of larger isoform was decreased by culturing cells beyond confluence. These findings suggest that CD44 isoform expression is cell type-specifically regulated in periodontium and altered according to growth phase of HGEC.