Indian System
The Indian blood group system comprises two specificities, ln a (= IN1) and ln b (= IN2)(1). The lna antigen is extremely rare in Europids but is found in 2–4% of Indians [4 ] and in more than 10% of some Arab and Iranian populations [5 ]; it has been des
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The six-digit ISST identification numbers (see Chap. 1) are 023 001 for Ina and 023 002 for Inb •
556 H. Schenkel-Brunner, Human Blood Groups © Springer-Verlag Wien 2000
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glycoprotein' [30,37], and the 'extracellular matrix receptor' (ECMRIII) or 'class III collagen receptor' (CRill) [7,16]. The CD44 glycoprotein is not only present on all circulating haematopoietic cells with the exception of platelets, but is also found in various tissue cells such as most mesenchymal cells (fibroblasts and smooth muscle), neuroectodermal cells, and endothelial and defined epithelial cells [15,34]. A highly homologous - if not identical - protein has also been detected in serum [31]. Moreover, the same glycoprotein is strongly expressed in different tumour tissues and in a spectrum of tumour cell lines of lymphoid, monocytic, epithelial, glial, and melanocytic origin [34,40].
CD44 is capable of binding to extracellular matrix components, such as hyaluronic acid [2,42], fibronectin [24], collagen types I and VI [7], heparan sulfate, [7], and the cytoskeletal protein ankyrin [27]. The broad tissue distribution of CD44 and its sequence relationship to cartilage link proteins (see below) suggest that this membrane constituent plays a general role in the adhesion of cell surfaces to extracellular glycosaminoglycan or collagen matrices. In lymphocytes CD44 is involved in mediating lymphocyte - endothelial cell interactions in the course of the recirculation of lymphocytes between the cardiovascular and lymphatic systems ('lymphocyte homing') [23,25]. Further studies have provided evidence that tumour cells in which CD44 levels are highly elevated use this same mechanism for metastatic spreading [19,20]. It has also been suggested that CD44 plays an important role in lymphocyte activation [13,21], control of lymphopoiesis [32], and cell - fibronectin interactions during erythropoiesis in haematopoietic progenitor cells [49]. CD44 is an acidic glycoprotein (pi -4.2) in which the major part of the negative charge is due to the presence of neuraminic acid and, to a lesser degree to the presence of sulfate groups. When the protein was isolated from lymphocytes and treated with endoglycosidases, it was recognised that the molecule bears 3-4 N-linked and several O-linked carbohydrate chains, the structures of which have not yet been investigated [25]. Some forms of the CD44 molecule contain covalently linked chondroitin-sulfate. Using radioiodinated Fab fragments, Anstee et al. [1] estimated a number of 6,000 to 10,000 copies of CD44 per red cell. A large number of CD44 isoforms have been detected [29]. These isoforms share the transmembrane region and the N-terminal 150 amino acids, but differ in the 557
24 INDIAN SYSTEM
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MDKFWWHAAW GLCLVPLSLA
-1
QIDLNITCRF AGVFHVEKNG RYSISRTEAA DLCKAFNSTL PTMAQMEKAL SIGFETCRYG
60
61 FIEGHVVIPR IHPNSICAAN NTGVYILTYN TSQYDTYCFN ASAPPEEDCT SVTDLPNAFD 120 121 GPITITIVNR DGTRVVQKGE YRTNPEDIYP SNPTDDDVSg gSSSERSSTg gGYIFYTFST 180 181 VHPIPDEDSP WITDSTDRIP ATRDQDTFHP ggGSHTTHES
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