Surface orientation and antigen properties of Rh and LW polypeptides of the human erythrocyte membrane

A glycosyltransferase-enriched reconstituted membrane system for the synthesis of branched O-linked glycans in vitro

Mimicking the biochemical reactions that take place in cell organelles is becoming one of the most important challenges in biological chemistry. In particular, reproducing the Golgi glycosylation system in vitro would allow the synthesis of bioactive glycan polymers and glycoconjugates for many future applications including treatments of numerous pathologies. In the present study, we reconstituted a membrane system enriched in glycosyltransferases obtained by combining the properties of the wheat germ lectin with the dialysable detergent n-octylglucoside. When applied to cells engineered to express the O-glycan branching enzyme core2 beta (1,6)-N-acetylglucosaminyltransferase (C2GnT-I), this combination led to the reconstitution of lipid vesicles exhibiting an enzyme activity 11 times higher than that found in microsomal membranes. The enzyme also showed a slightly higher affinity than its soluble counterpart toward the acceptor substrate. Moreover, the use of either the detergent re-solubilization, glycoprotein substrates or N-glycanase digestion suggests that most of the reconstituted glycosyltransferases have their catalytic domains in an extravesicular orientation. Using the disaccharide substrate Galβ1-3GalNAc-O-p-nitrophenyl as a primer, we performed sequential glycosylation reactions and compared the recovered oligosaccharides to those synthesized by cultured parental cells. After three successive glycosylation reactions using a single batch of the reconstituted vesicles and without changing the buffer, the acceptor was transformed into an O-glycan with chromatographic properties similar to glycans produced by C2GnT-I-expressing cells. Therefore, this new and efficient approach would greatly improve the synthesis of bioactive carbohydrates and glycoconjugates in vitro and could be easily adapted for the study of other reactions naturally occurring in the Golgi apparatus such as N-glycosylation or sulfation.

LW protein: a promiscuous integrin receptor activated by adrenergic signaling

The LW blood group antigen glycoprotein, although part of the Rh macromolecular complex, is nonetheless a member of the intercellular adhesion molecule (ICAM) family. Thus, while it is only rarely clinically important in the setting of transfusion and pregnancy, LW is likely to contribute to red cell adhesion in a variety of settings, including during hematopoiesis, as well as in vascular disorders. The best documentation of a pathophysiological role for LW in human disease is in sickle cell disease, where it contributes to red cell adhesion to endothelial cells and the development of vaso-occlusion, the hallmark of that disease. LW may also contribute to other intravascular processes, such as both venous and arterial thrombosis, due to its ability to interact with both activated platelets as well as leukocytes. The evidence that LW itself can undergo activation on red cells holds promise that pharmacotherapeutic maneuvers may be found to prevent such pathophysiologic interactions.

Autoimmune haemolytic anaemia complicating haematopoietic cell transplantation in paediatric patients: high incidence and significant mortality in unrelated donor transplants for non-malignant diseases

Haemolytic anaemia is a recognized complication of haematopoietic cell transplantation (HCT) and can result from alloimmune- or autoimmune-derived antibodies. Unlike alloimmune haemolytic anaemia, autoimmune haemolytic anaemia (AIHA) is poorly understood, particularly in the paediatric population where only case reports have been published. Between January 1995 and July 2001, 439 consecutive allogeneic HCT were performed in paediatric patients at the University of Minnesota, 31% (n = 136) from related donors (RD) and 69% (n = 303) from unrelated donors (URD). Nineteen cases of AIHA were identified with documented significant haemolysis and a positive direct antiglobulin test. All cases of AIHA occurred in URD transplants, yielding a cumulative incidence of AIHA post-transplant of 6% at 1 year. Patients transplanted for non-malignant disease, particularly metabolic diseases, had a higher incidence of AIHA post-HCT when compared with patients transplanted for malignancies (RR 4.2 95% CI 1.2-15.4, P = 0.01). Mortality was high in our series of 19 patients with 10 (53%) dying following the onset of AIHA, three as a direct consequence of haemolysis. Fifty per cent of deaths occurred from infection while on immunosuppressive therapy to treat haemolysis. Alternative treatment strategies were employed, with the majority of patients demonstrating disease refractory to traditional steroid therapy.

Integrin receptor specificity for human red cell ICAM-4 ligand. Critical residues for alphaIIbeta3 binding

The red cell intercellular adhesion molecule-4 (ICAM-4) binds to different members of the integrin receptor families. To better define the ICAM-4 integrin receptor specificity, cell transfectants individually expressing various integrins were used to demonstrate that alphaLbeta2, alphaMbeta2, and alphaIIbbeta3 (activated) bind specifically and dose dependently to the recombinant ICAM-4-Fc protein. We also show that cell surface ICAM-4 interacts with the cell surface alphaVbeta3 integrin. In addition, using a alpha4beta1 cell transfectant and beta2 integrin-deficient LAD cells, we show here that ICAM-4 failed to interact with alpha4beta1 even after alpha4beta1 activation by phorbol ester or with the monoclonal antibody TS2/16 (+ Mn2+). ICAM-4 amino acids that are critical for alphaIIbbeta3 and alphaVbeta3 interaction were identified by domain deletion analysis, site-directed mutagenesis and synthetic peptide inhibition. Our results provide evidence that the beta3 integrin binding sites encompass the first and second Ig-like domains of ICAM-4. However, while the alphaIIbbeta3 contact site comprises the ABED face of domain D1 with an extension in the C'-E loop of domain D2, the alphaVbeta3 contact site comprises residues on both faces of D1 and in the C'-E loop of D2. These data, together with our previous results, demonstrate that different integrins bind to different but partly overlapping sites on ICAM-4, and that ICAM-4 may accommodate multiple integrin receptors present on leukocytes, platelets and endothelial cells.

Identification of critical amino-acid residues on the erythroid intercellular adhesion molecule-4 (ICAM-4) mediating adhesion to alpha V integrins

Intercellular adhesion molecule-4 (ICAM-4, syn. LW glycoprotein) interacts with the integrins alpha(L)beta(2), alpha(M)beta(2), A(4)beta(1), the alpha(V) family, and alpha(IIb)beta(3). Systematic mutagenesis of surface-exposed residues conserved between human and murine ICAM-4 defined 12 single amino-acid changes that affect the interaction of ICAM-4 with alpha(V) integrins. Mutation of 10 of these residues, 8 of which are spatially close on the surface of the molecule, led to a reduction in adhesion. Moreover, peptides corresponding to regions of ICAM-4 involved in its interaction with alpha(V) integrins inhibited these interactions. The other 2 mutations increased the extent of interaction of ICAM-4 with alpha(V) integrins. These mutations appear to prevent glycosylation of N160, suggesting that changes in glycosylation may modulate ICAM-4-alpha(V) integrin interactions. The region of ICAM-4 identified as the binding site for alpha(V) integrins is adjacent to the binding sites for alpha(L)beta(2) and alpha(M)beta(2). Selective binding of ICAM-4 to different integrins may be important for a variety of normal red cell functions and also relevant to the pathology of thrombotic disorders and vasoocclusive events in sickle cell disease. Our findings suggest the feasibility of developing selective inhibitors of ICAM-4-integrin adhesion of therapeutic value in these diseases.

Cell adhesion molecules, leukocyte trafficking, and strategies to reduce leukocyte infiltration

Leukocyte-endothelial cell interactions are mediated by various cell adhesion molecules. These interactions are important for leukocyte extravasation and trafficking in all domestic animal species. An initial slowing of leukocytes on the vascular endothelium is mediated by selectins. This event is followed by (1) activation of beta2 integrins after leukocyte exposure to cytokines and pro-inflammatory mediators, (2) adherence of leukocyte beta2 integrins to vascular endothelial ligands (eg, intercellular adhesion molecule-1 [ICAM-1]), (3) extravasation of leukocytes into tissues through tight junctions of endothelial cells mediated by platelet and endothelial cell adhesion molecule-1 (PECAM-1), and (4) perivascular migration through the extracellular matrix via beta1 integrins. Inhibiting excessive leukocyte egress and subsequent free radical-mediated damage caused by leukocyte components may attenuate or eliminate tissue damage. Several methods have been used to modify leukocyte infiltration in various animal models. These methods include nonspecific inhibition of pro-inflammatory mediators and adhesion molecules by nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, inhibition of cytokines and cytokine receptors, and inhibition of specific types of cell adhesion molecules, with inhibitors such as peptides and antibodies to beta2 integrins, and inhibitors of selectins, ICAMs, and vascular cell adhesion molecule-1 (VCAM-1). By understanding the cellular and molecular events in leukocyte-endothelial cell interactions, therapeutic strategies are being developed in several animal models and diseases in domestic animal species. Such therapies may have clinical benefit in the future to overcome tissue damage induced by excessive leukocyte infiltration.

Binding sites of leukocyte beta 2 integrins (LFA-1, Mac-1) on the human ICAM-4/LW blood group protein

The red cell ICAM-4/LW blood group glycoprotein, which belongs to the family of intercellular adhesion molecules (ICAMs), has been reported to interact with CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1) beta(2) integrins. To better define the basis of the ICAM-4/beta(2) integrin interaction, we have generated wild-type, domain-deleted and mutated recombinant chimeric ICAM-4-Fc proteins and analyzed their interaction in a cellular adhesion assay with LFA-1 and Mac-1 L-cell stable transfectants. We found that monoclonal antibodies against CD11a, CD11b, CD18, or LW(ab) block adhesion of transfectant L-cells to immobilized ICAM-4-Fc protein and that the ICAM-4/beta(2) integrin interaction was highly sensitive to the presence of the divalent cations Ca(2+) and Mg(2+). Deletion of individual Ig-domains D1 or D2 of the extracellular part of ICAM-4 showed that LFA-1 binds to the first Ig-like domain, whereas the Mac-1 binding site encompassed both the first and the second Ig-like domains. Based on the crystal structure of ICAM-2, we propose a model for the Ig-like domains D1 and D2 of ICAM-4. Accordingly, by site-directed mutagenesis of 22 amino acid positions spread out on all faces of the ICAM-4 molecule, we identified four exposed residues, Leu(80), Trp(93), and Arg(97) on the CFG face and Trp(77) on the E-F loop of domain D1 that may contact LFA-1 as part of the binding site. However, the single and double mutants R52E and T91Q on the CFG face of domain D1, which correspond to the key residues Glu(34) and Gln(73) for ICAM-1 binding to LFA-1, had no effect on LFA-1 binding. In contrast, all mutants on the CFG face of domain D1 and residues Glu(151) and Thr(154) in the C'-E loop of the domain D2 seem to play a dominant role in Mac-1 binding. These data suggest that the binding site for LFA-1 on ICAM-4 overlaps but is distinct from the Mac-1 binding site.

Insights into the structure and function of membrane polypeptides carrying blood group antigens

In recent years, advances in biochemistry and molecular genetics have contributed to establishing the structure of the genes and proteins from most of the 23 blood group systems presently known. Current investigations are focusing on genetic polymorphism analysis, tissue-specific expression, biological properties and structure-function relationships. On the basis of this information, the blood group antigens were tentatively classified into five functional categories: (i) transporters and channels, (ii) receptors for exogenous ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes and, (v) structural proteins. This review will focus on selected blood groups systems (RH, JK, FY, LU, LW, KEL and XK) which are representative of these classes of molecules, in order to illustrate how these studies may bring new information on common and variant phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in nonerythroid lineage.

Genetic and Immunological Properties of Phage-Displayed Human Anti-Rh(D) Antibodies: Implications for Rh(D) Epitope Topology

Understanding anti-Rh(D) antibodies on a molecular level would facilitate the genetic analysis of the human immune response to Rh(D), lead to the design of therapeutically useful reagents that modulate antibody binding, and provide relevant information regarding the structural organization of Rh(D) epitopes. Previously, we described a Fab/phage display-based method for producing a large array of anti-Rh(D) antibodies from the peripheral blood lymphocytes of a single alloimmunized donor. In the current study, we present a detailed analysis of 83 randomly selected clones. Sequence analysis showed the presence of 28 unique γ1 heavy chain and 41 unique light chain gene segments. These paired to produce 53 unique Fabs that had specificity for at least half of the major Rh(D) epitopes. Surprisingly, despite this diversity, only 4 closely related heavy chain germline genes were used (VH3-30, VH3-30.3, VH3-33, and VH3-21). Similarly, nearly all Vκ light chains (15/18) were derived from one germline gene (DPK9). λ light chains showed a more diverse VL gene usage, but all (23/23) used the identical Jλ2 gene. Several Fabs that differed in epitope specificity used identical heavy chains but different light chains. In particular, 2 such clones differed by only 3 residues, which resulted in a change from epD2 to epD3 specificity. These results suggest a model in which footprints of anti-Rh(D) antibodies are essentially identical to one another, and Rh(D) epitopes, as classically defined by panels of Rh(D) variant cells, are not discrete entities. Furthermore, these data imply that the epitope specificity of an anti-Rh(D) antibody can change during the course of somatic mutation. From a clinical perspective, this process, which we term epitope migration, has significance for the design of agents that modulate antibody production and for the creation of mimetics that block antibody binding in the settings of transfusion reactions and hemolytic disease of the newborn.

The red cell LW blood group protein is an intercellular adhesion molecule which binds to CD11/CD18 leukocyte integrins

Leukocyte adhesion involves the leukocyte-specific integrins CD11a/CD18, CD11b/CD18 and CD11c/CD18, which bind to intercellular adhesion molecules (ICAM). Three ICAM have been described, and are expressed on leukocytes and various other cells, but are absent from red cells. Here, we show that the red cell Landsteiner-Wiener (LW) blood group glycoprotein is an ICAM which binds to the leukocyte-specific integrins. This finding has important implications in red cell physiology.

Biochemical aspects of the blood group Rh (rhesus) antigens

Despite their importance in clinical haematology, the details of the structures and possible functions of the proteins associated with Rh antigen expression have only recently begun to emerge. The antigens are carried by a multimeric complex between a M(r) 30,000 polypeptide which is not glycosylated (the Rh30 polypeptide), and a heavily glycosylated glycoprotein (the Rh50 glycoprotein). The N-terminal amino acid sequences of the two types of proteins were determined and used to isolated cDNA clones. The Rh30 and Rh50 proteins are both very hydrophobic membrane proteins, each containing up to 12 membrane spans. The two proteins are homologous in sequence and clearly belong to the same family. They are erythroid-specific and not related to any other known family of proteins. The Rh30 polypeptides are the genetic determinants of Rh blood group antigen activity. One polypeptide (Rh30A) is probably associated with CcEe antigen activity, while another (Rh30B) is responsible for the D antigen. The proteins have structures typical of transporters but their functions are still unclear. A number of other red cell membrane proteins (LW, CD47, glycophorin B and Fy) show alterations in red cells lacking Rh antigens (Rhnull). These proteins may have a role in the biosynthesis or function of the Rh30 and Rh50 proteins.