ICAM-4 (LW blood group glycoprotein) is an erythroid-specific membrane component that belongs to the family of intercellular adhesion molecules and interactsThe main physiological function of red blood cells (RBCs), 1 which encapsulate hemoglobin, is to ensure the respiratory gases transport throughout the human body. However, the recent demonstration that mature RBCs express a growing number of adhesion molecules, many of which exhibit blood group specificities (1-3), reinforces the necessity to revisit the functional interaction of RBCs with leukocytes, platelets, and vascular endothelium under normal and pathological conditions.It is interesting that many RBC adhesion molecules contain protein domains characteristic of the immunoglobulin superfamily, suggesting some recognition function. These molecules might participate in the normal RBC physiology by playing a role during erythropoiesis (differentiation, maturation, enucleation, release), self-recognition mechanisms, red cell turnover, and cell aging through cellular interactions with counter

Rhnull human erythrocytes lack the antigens of the Rhesus blood-group system, have an abnormal shape, have an increased osmotic fragility, and are associated with mild chronic haemolytic anaemia. Rhnull erythrocytes also lack all antigens of the LW blood-group system, but the functional significance of this deficiency is unknown. We have identified, by immunoblotting with two mouse monoclonal antibodies (BS46 and BS56), the LW-active component(s) in normal human erythrocytes as a broad band of Mr 37 000-47 000 on SDS/polyacrylamide-gel electrophoresis. Treatment of intact human erythrocytes with endoglycosidase F preparation destroyed the epitopes recognized by antibodies BS46 and BS56, suggesting that one or more N-glycosidically linked oligosaccharides are required for the formation of the LW antigens. Estimation of the number of LW antigen sites per erythrocyte by using radioiodinated purified antibody BS46 gave average values of 4400 molecules/cell for Rh(D)-positive adult erythrocytes and 2835 molecules/cell for Rh(D)-negative adult erythrocytes. Like the Rh(D) polypeptide, the LW polypeptide(s) is (are) associated with the cytoskeleton of normal erythrocytes. These results suggest the possibility that the absence of the LW polypeptide may also contribute to the functional and/or morphological abnormalities of Rhnull erythrocytes.

The LW blood group antigens reside on a 42-kDa erythrocyte membrane glycoprotein that was purified by immunoaffinity and partiafly sequenced. From this information, a specific PCR-amplifled DNA fragment was used to screen a Agtll human bone marrow cDNA library. LW(a-b-). This showed that the protein encoded by these clones was LW gene product and suggested that the N terminus of the LW protein is oriented extracellularly. Most interestingly, the LW protein was found to exhibit sequence similarities (with -30% identity) with intercellular adhesion molecules ICAM-1, -2, and -3, which are the counterreceptors for the lymphocyte functionassociated antigens LFA-1. The extraceflular domain of LW consists, like that of ICAM-2, of two immunoglobulin-like doins, and the critical residues involved in the binding of LFA-1 to ICAMs were partially conserved in LW.The LW and Rh (rhesus) blood group systems were discovered simultaneously and were confused for a long time (reviews, refs. 1-3 Affinity Purification of the LW Protein. Membranes from two units of LW(a+b-) red cells were solubilized with 1% (wt/vol) Triton X-100 in phosphate-buffered saline (PBS) and applied to a specific affinity matrix column, prepared by binding 9 mg of purified murine monoclonal IgG antibody anti-LW (BS46) to 2 ml of protein A-agarose followed by cross-linking of the complex with dimethylpimelimidate (ImmunoPure IgG orientation kit, Pierce). After washing, the LW antigenic material bound was eluted with a glycine buffer (pH 2.8) and immediately brought to near neutrality.

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