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Indian Blood Group System

Gene locus - CD44


The epitopes for the Indian system reside on a type I 80 kDa membrane glycoprotein, known as CD44 antigen (also known as the lymphocyte homing receptor, human hyaluronate receptor). It is an adhesion molecule that can bind to various extracellular matrix components. Two domains, important for hyaluronate binding have been identified. The protein is extensively glycosylated bearing both N- and O-linked glycans and contains potential chondroitin sulphate linkage sites near its amino terminus.

The genes

CD44 gene spans ~ 50kb and is organized into 19 exons, of which 10 are variable. Different isofoms, resulting from alternative splicing have been observed in different tissues, but the major form is the 80 kDa species expressed predominantly in hematopoietic and lymphoid tissues. The hematopoetic isoform is encoded by exons 1-5,15-17 and 19. So far only two antithetical antigenic specificities have been documented Ina and Inb.

Function of proteins

Plays a role in adhesion, between cells and adhesion of cells to hyaluronate, fibronectin, collagen and other components of the extracellular matrix. It is involved in immune stimulation and signaling between cells.

Tissue distribution

In erythrocytes and other blood cells such as neutrophils, lymphocytes, monocytes. Also, in most tissues, brain, breast, epithelium, intestine, heart, kidney, liver, lung, placenta, skin, spleen, thymus. In cell lines, fibroblasts, K652, HEL, HL-60, IM-9, MOLT4 (weak) but not on Raji, Daudi or Jurkat cells.

Disease association

CD44 may play a role in metastatic spreading of tumor cells. Serum CD44 is elevated in some patients with lymphoma. Joint fluid from patients with inflammatory synovitis has higher than normal levels of soluble CD44 (Moulds J.M. in Immunology of Transfusion Medicine ,Garratty G., ed., M. Dekker, NY, 273-297, 1994).Antibodies to Ina or Inb may cause hemolytic transfusion reactions.

About the alleles

So far, only two antigens in addition to Ina and Inb have been documented.The occurrence of the Inb is universally common in the population whereas Ina has a relatively high frequency in some Middle Eastern and Indian populations only. Thus, the highest frequency is among Arabs (11.8%), Iranians (10.6%) and South Asian Indians (4%), with only 0.1% frequency among Caucasians, Asians and Blacks. The DNA change defining the Inb to Ina phenotype is at 137G>C; thus, Inb is specified by an Arg and Ina by a Pro. In the list of alleles, the sequence, M59040, of CD44 exhibiting Inb (In a-b+ blood group phenotype) is taken as reference (codon 1 starts at nucleotide 29).

One should keep in mind, that the occurrence of isoforms characteristic of the In protein may pose a problem in the selection and use of the reference sequence.

When searching for a particular allele, use "name" if DNA alteration is known or, if you wish to search by phenotype or the designation used by the author, use "alias"(see "Details").

Other database IDs and links

NCBI genes Uniprot ID Genbank proteins Gene nomenclature database ID Genbank nucleic acids NCBI homologenes for homologs and orthologs NCBI dbSNP for single nucleotide polymorphisms OMIM ID - at Online Mendelian Inheritance in Man


New PubMed entries with the terms Indian and blood from the last 30 days.
NCBI Book Sections with the terms Indian and blood.


Marion E. Reid and Christine Lomas-Francis, Immunohematology, New York Blood Center, 310 East 67 St., New York, N.Y. 10021

Contributors for specific alleles are listed with the alleles.


Updated 2014-06-12 17:44:10.447
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