Blood Group Antigen Gene Mutation Database

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Indian Blood Group System

Introduction

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 In^a and In^b.

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)

About the alleles

So far, only two antigens in addition to In^a and In^b have been documented.The occurrence of the In^b is universally common in the population whereas In^a 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 or Inb is specified by an Arg and Ina by a Pro. In the list of alleles, the sequence, acc.no. M59040, of CD44 exhibiting In^b (In a-b+ blood group phenotype) is taken as reference (codon 1 starts at nucleotide 29).

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").