cDNA sequence for the alpha M subunit of the human neutrophil adherence receptor indicates homology to integrin alpha subunits

Molecular Genetics of the Human Neutrophil Antigens

BACKGROUND AND OBJECTIVE

Antibodies to human neutrophil antigens (HNAs) have been implicated in transfusion-related acute lung injury and allo- and autoimmune neutropenia. To date, five HNA systems are assigned, and during the last decades enormous efforts have been undertaken to identify the underlying genes and to characterize the antigens. This review of the literature will provide the current genetic, molecular and functional information on HNAs.

RECENT FINDINGS

New information on alleles and antigens has been added to nearly each of the five HNA systems. HNA-1d has been added as the antithetical epitope to HNA-1c that is located on the glycoprotein encoded by FCGR3B*02 but not by FCGR3B. FCGR3B*04 and *05 now are included as new alleles. A CD177*787A>T substitution was demonstrated as the main reason for the HNA-2-negative phenotype on neutrophils. The target glycoprotein of HNA-3 antibodies could be identified as choline transporter-like protein 2 (CTL2) encoded by SLC44A2. The conformation sensitive epitope discriminates between arginine and glutamine at position 152 resulting in HNA-3a and HNA-3b. An additional Leu151Phe substitution can impair HNA-3a antibody binding. Recently an alloantibody against HNA-4b which discriminates from HNA-4a by an Arg61His exchange of the glycoprotein encoded by the ITGAM gene was reported in neonatal alloimmune neutropenia. An update of the current HNA nomenclature based on the new findings was provided in 2016 by the ISBT Granulocyte Immunobiology Working Party nomenclature subcommittee.

CONCLUSIONS

The molecular basis of each of the five HNA antigen systems has been decoded during the past decades. This enables reliable molecular typing strategies, antibody detection and specification as well as development of new assays based on recombinant antigens. However, research on HNA alleles, antigens, and antibodies is not finally terminated and also in the future will add new findings.

Structure-Function Relationships Underlying the Capacity of Bordetella Adenylate Cyclase Toxin to Disarm Host Phagocytes

Bordetellae, pathogenic to mammals, produce an immunomodulatory adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) that enables them to overcome the innate immune defense of the host. CyaA subverts host phagocytic cells by an orchestrated action of its functional domains, where an extremely catalytically active adenylyl cyclase enzyme is delivered into phagocyte cytosol by a pore-forming repeat-in-toxin (RTX) cytolysin moiety. By targeting sentinel cells expressing the complement receptor 3, known as the CD11b/CD18 (α_Mβ₂) integrin, CyaA compromises the bactericidal functions of host phagocytes and supports infection of host airways by Bordetellae. Here, we review the state of knowledge on structural and functional aspects of CyaA toxin action, placing particular emphasis on signaling mechanisms by which the toxin-produced 3',5'-cyclic adenosine monophosphate (cAMP) subverts the physiology of phagocytic cells.

The cytoplasmic domain of FcgammaRIIA (CD32) participates in phagolysosome formation

Signaling motifs located within the cytoplasmic domain of certain receptors contribute to lysosome fusion. Most studies have described lysosome fusion with respect to endocytic receptors. Phagolysosome fusion has not been extensively studied. To test the hypothesis that the tail of FcgammaRIIA participates in phagolysosomal fusion, a "reverse" genetic complementation system was used. It was previously shown that complement receptor type 3 (CR3) can rescue the phagocytic activity of a mutant FcgammaRIIA lacking its cytoplasmic domain (tail-minus form). This system has allowed us to study Fcgamma receptor-dependent phagocytosis and phagolysosome fusion in the presence and absence of the cytoplasmic domain of FcgammaRIIA. Fluorescent dextran was used to label lysosomes. After target internalization, wild-type FcgammaRIIA-mediated phagolysosome formation was observed as indicated by colocalization of fluorescent dextran and the phagosome. In addition, when studying mutants of FcgammaRIIA containing a full-length cytoplasmic tail with the 2 ITAM tyrosines mutated to phenylalanine, (1) phagocytosis was abolished, (2) CR3 restored phagocytosis, and (3) lysosomal fusion was similar to that observed with the wild-type receptor. In contrast, in the presence of CR3 and the tail-minus form of FcgammaRIIA, internalized particles did not colocalize with dextran. Electron microscopy revealed that the lysosomal enzyme acid phosphatase colocalized with immunoglobulin G-coated targets internalized by wild-type FcgammaRIIA but not by tail-minus FcgammaRIIA and CR3. Thus, the tail of FcgammaRIIA contributes to phagolysosome fusion by a mechanism that does not require a functional ITAM sequence.

Molecular cloning of a novel myeloid granule protein

Granulocytes are recognized by the presence of granules, including primary (azurophilic) and secondary types. Each granule type contains distinct and characteristic families of enzymes. We have screened a murine bone marrow cDNA library to obtain a series of sequences corresponding to mRNAs which are both myeloid-specific and appear to be expressed only in immature bone marrow cells. A 1,160 bp sequence (B9) has been isolated, which shows restricted expression in murine bone marrow, with the highest levels in cultures enriched for promyelocytes. Translation yields a single open reading frame of 167 amino acids and a calculated MW of 19.33 kd. A single potential N-glycosylation site is present. Evaluation of the amino terminal sequence shows 2 polar amino acids flanking a hydrophobic region, suggesting a signal sequence and the possibility of post-translational modification. An extensive search of the protein data base reveals 30% identity over 90 amino acids with porcine cathelin, a cystatin-like cysteine proteinase inhibitor. This sequence identity includes conservation of the 4 cysteine residues noted in all members of the cystatin superfamily. In an attempt to further characterize this novel sequence, a polyclonal antiserum was prepared by immunization with a 20 amino acid synthetic peptide corresponding to a unique portion of the carboxy terminus. Immunoelectron microscopy localized B9 to neutrophilic granules. We have identified a novel myeloid-specific granule protein related to porcine cathelin, but showing important structural differences. This may represent the first isolated member of a new cystatin family. More importantly, the small size of the B9 gene and its tight pattern of early expression make B9 an excellent reporter molecule for the study of new factors important in myeloid differentiation.

Investigation of the complement receptor 3 (CD11b/CD18) in human rectal epithelium

Rectal and cervicovaginal mucosa are common routes of transmission of HIV, although the mechanism of transmission is unknown. We have investigated human rectal and cervicovaginal epithelia for the expression of complement receptors (CR) and cell adhesion molecules which may be involved in HIV and other infections. In rectal mucosa, CR3 was detected in the surface and crypt epithelial cells by immunohistology, using MoAbs to CD18 and CD11b in 10 out of 15 specimens. RNA transcripts encoding both CD11b and CD18 were also demonstrated in surface and crypt epithelial cells by in situ hybridization. Although CD11b was detected in the epithelial cells in three out of the 14 cervicovaginal specimens, we were unable to detect CD18. We suggest that expression of the CD11b/CD18 heterodimer might facilitate transmission of HIV by enhancing binding of HIV-antibody complexes in seminal fluid to epithelial cells. Alternatively, since intercellular adhesion molecule-1 (ICAM-1) is a receptor for CD11b/CD18, this may promote adhesion between epithelial cells and HIV-infected mononuclear cells in seminal fluid.

Inhibition of neural crest cell attachment by integrin antisense oligonucleotides

Neural crest cell interactions with extracellular matrix molecules were analyzed with the use of antisense oligonucleotides to block synthesis of integrin subunits. When added to the culture medium of quail neural crest cells, selected antisense phosphorothiol oligonucleotides reduced the amounts of cell surface alpha 1 or beta 1 integrin subunits by up to 95 percent and inhibited neural crest cell attachment to laminin or fibronectin substrata. Differential effects on specific alpha integrins were noted after treatment with alpha-specific oligonucleotides. Cells recovered the ability to bind to substrata 8 to 16 hours after treatment with inhibitory oligonucleotides. The operation of at least three distinct alpha integrin subunits is indicated by substratum-selective inhibition of cell attachment.

Expression and function of beta 2 integrins on alveolar macrophages from human and nonhuman primates

The alveolar macrophage (AM) participates in diverse, adherence-related activities required for host defense and the inflammatory response. The beta 2 integrins (the CD11/CD18 heterodimer) mediate some of these activities on circulating leukocytes and peritoneal macrophages. We investigated expression of the CD11/CD18 leukocyte integrin subunits on AMs obtained by bronchoalveolar lavage of human and nonhuman primates. We also determined the role of the CD11/CD18 complex in AM chemotaxis and adherence to A549 alveolar epithelial cell monolayers. Immunofluorescence flow cytometry indicated that the CD11a/CD18 complex was expressed in high levels and CD11b/CD18 and CD11c/CD18 in lower levels on the AM surface. Northern blot analysis indicated the presence of CD11a, CD11c, and CD18 mRNA in the AMs. Smaller quantities of CD11b mRNA were also found. AM chemotaxis to zymosan-activated serum was markedly inhibited by a monoclonal antibody to CD18. In addition, adherence of AMs to A549 cells (stimulated by tumor necrosis factor to upregulate intercellular adhesion molecule-1 expression) was decreased from 30.3 +/- 5.0 to 20.8 +/- 2.4% (P less than 0.05) by the same monoclonal antibody. We conclude that: (1) AMs obtained from human and nonhuman primates constitutively express predominantly CD11a/CD18 surface antigen and mRNA, (2) chemotaxis of AMs is CD18 dependent, and (3) adhesion of AMs to an alveolar epithelial cell monolayer is partly but not completely dependent on the beta 2 integrins.

Establishment of a novel granulocytic sarcoma cell line which can adhere to dermal fibroblasts from a patient with granulocytic sarcoma in dermal tissues and myelofibrosis

A novel human myeloid cell line, designated HSM-1, has been established from the pleural effusion of a patient with granulocytic sarcoma (GS) who had been followed as having primary myelofibrosis for 10 years. When he was diagnosed as having granulocytic sarcoma in dermal tissues, no evidence of malignant transformation into leukaemia was found in both the peripheral blood and bone marrow. The established cell line was positive for myeloperoxidase, Sudan black B, Naphthol AS-D chloroacetate esterase. Surface marker analysis revealed that HSM-1 expressed CD4, CD13, CD11a, CD11b, Leu8, CD49b, CD49d, CD49e, CD29 and HLA-DR. To clarify why the unusual myeloid tumours developed in non-haematopoietic tissues, we examined the capability of HSM-1 to bind to skin fibroblast layers. The HSM-1 cells were found to bind to both bone marrow stromal layers and skin fibroblast layers. Among the other myeloid cell lines tested, none was found to bind to skin fibroblast layers. These findings suggest that the GS cell line may be derived from a haematopoietic precursor cell which can bind to skin fibroblasts and is localized in non-haematopoietic tissues resulting in the formation of extramedullary myeloid metaplasia. HSM-1 is a useful tool for analysing the characteristics of granulocytic sarcoma and homing receptors for haematopoietic stem cells.

Identification of the promoter of the myelomonocytic leukocyte integrin CD11b

The CD11b (or macrophage-1 antigen; MAC-1) subunit of the leukocyte integrin family forms a noncovalently associated heterodimeric structure with the CD18 (beta) subunit on the surface of human granulocytes and monocyte/macrophages, where it enables these myeloid cells to participate in a variety of adherence-related activities. Expression of the CD11b subunit is restricted to cells of the myelomonocytic lineage and depends upon the stage of differentiation with the most mature myeloid cells expressing the highest levels of CD11b. To study the regulation of CD11b expression, a genomic clone corresponding to the 5' region of the CD11b gene was isolated from a human chromosome 16 library. Primer extension and RNase protection assays identified two major transcriptional start sites, located 90 base pairs and 54 base pairs upstream from the initiation methionine. DNA sequence analysis of 1.7 kilobases of the 5' flanking sequence of the CD11b gene indicated the absence of a "CAAT" or "TATA" box; however, potential binding sites for the transcription activators Sp1, PU.1, ets, and AP-2 are present, as well as retinoic acid response elements. The 1.7-kilobase CD11b promoter sequence displayed functional activity in transient transfection assays in the monocytic cell line THP-1 and the myeloid cell line HL-60. In contrast, this 1.7-kilobase promoter sequence did not display functional activity in the Jurkat T-lymphoid cell line. Detailed characterization of the CD11b promoter sequence should provide insight into the molecular events regulating the tissue-specific and developmental stage-specific expression of the CD11b molecule in myelomonocytic cells.

Leukocyte adhesion molecules deficiency: its structural basis, pathophysiology and implications for modulating the inflammatory response

Understanding the molecular basis of a rare inherited disease, Leu-CAM deficiency in humans, has underscored the importance of the cellular component of inflammation and unravelled the complex series of homotypic and heterotypic cell interactions necessary for mobilization of leukocytes to infected sites. Furthermore, this disease has shown that several apparently distinct cellular inflammatory responses (e.g. aggregation, adhesion to endothelium, directed migration and phagocytosis) are mechanistically related and mediated by a set of molecules which belong to a larger group of adhesion molecules (Integrins) mediating similar phenomena critical for immune surveillance, lymphocyte homing, morphogenesis and thrombogenesis. This disease also showed the relative biologic importance of CD11/CD18 in leukocytes. CD11/CD18 are more critical for the functions of phagocytic cells as compared to lymphocytes although similar inhibitory effects of anti-CD11/CD18 mAbs can be demonstrated in vitro. Expression and function of CD11/CD18 is regulated at several levels which include formation of stable heterodimers, qualitative changes in the receptor and quantitative changes in the levels of expression of the receptors and their ligands. We have identified inherited single amino acid substitutions on CD18 which impair heterodimer formation and cell surface expression, thus accounting for the pathogenesis of Leu-CAM deficiency. We also found a stimulus-induced phosphorylation of CD18, which is transient in nature when elicited through other surface receptors. This may be important in regulation of CD11/CD18 receptor avidity, recycling, endocytosis and cross-talk with other receptors. Finally, realization of the profound impairment in the acute cellular inflammatory response present in Leu-CAM deficiency has permitted novel ways of controlling the inflammatory response in several situations were inflammation serves an injurious rather than a beneficial role to the host.

The leukocyte cell surface receptor(s) for the iC3b product of complement

CR3 is probably the major adhesion molecule on monocytes and neutrophils. Its function as a phagocytic receptor for iC3b-coated particles has been well characterized. CR3 also has binding affinity for other ligands, including those that compete with iC3b such as fibrinogen, factor X, and beta-glucan, and those that do not such as bacterial LPS. CR3 binding to endothelial cells probably plays an important role in the extravascular migration of monocytes and neutrophils, but the ligand that it recognizes on endothelial cells has not been identified. Structurally CR3 belongs to the integrin family, and it shares a common subunit with p150,95 and LFA-1. The expression of these three membrane antigens appear to be limited to leukocytes, and they are sometimes referred to collectively as the leukocyte integrins. All three antigens have a common binding affinity for bacterial LPS. p150,95 also has affinity for iC3b, but p150,95/iC3b-dependent cellular responses has not been demonstrated. Its status as a complement receptor therefore awaits further experimental support.

Isolation and characterization of Chinese hamster ovary cell variants deficient in the expression of fibronectin receptor

Chinese hamster ovary cell populations were enriched for cells displaying low surface expression of the 140-kD integrin fibronectin receptor (FnR) by means of fluorescence-activated cell sorting using monoclonal anti-FnR antibodies. Selected cells were cloned by limiting dilution, and the resulting clones were screened for low cell surface FnR expression by ELISA. Two multiply sorted populations gave rise to variant clones possessing approximately 20 or 2% FnR expression, respectively, compared with wild-type cells. Growth rates of the "20%" and "2%" clones on serum-coated plastic dishes were similar to that of wild-type cells. Variant cells expressing 20% FnR could attach and spread on substrata coated with purified fibronectin, although somewhat more slowly than wild-type cells, while cells expressing 2% FnR could not attach or spread. Cells from all variant clones attached normally to vitronectin substrata, but some of the 2% clones displayed altered morphology on this type of substratum. Motility assays in blind well chambers showed a correlation of movement with level of expression of FnR. The number of cells migrating in response to fibronectin was greatly reduced compared with wild-type cells for the 20% FnR variant clones, while variant clones with 2% FnR showed virtually no migratory activity. Surface labeling with 125I and immunoaffinity purification of FnR showed reduced levels of intact FnR on the plasma membranes of variants with 20% FnR, while none was detected in variants expressing 2% FnR. Nevertheless, beta subunits were detected on the surfaces of all variant clones. Immunoblots of cell lysates from wild-type cells and from both types of variant clones showed substantial amounts of FnR beta chain as well as enhanced amounts of a pre-beta moiety in the variants. alpha chain was markedly reduced in the 20% variants and essentially absent in the 2% variants, indicating that failure to assemble intact FnR in these variants was due to deficiencies of alpha chain production. Dot blots of total mRNA from a representative clone expressing 20% FnR showed reduced levels of material hybridizing to an 0.97-kb hamster FnR alpha chain cDNA probe as compared with wild type, while mRNA from a representative clone expressing 2% FnR had no detectable hybridizable RNA; this seems to agree well with the results obtained by immunoblotting. Thus, the defect in the variant clones seems to be due to reduced levels of alpha chain mRNA leading to a deficit of mature FnR and consequent alterations in cell adhesion and motility on fibronectin substrata.