Deficiency of a surface membrane glycoprotein (Mo1) in man

Neutrophil migration across a cultured intestinal epithelium. Dependence on a CD11b/CD18-mediated event and enhanced efficiency in physiological direction

Neutrophils (PMN) migrate across intestinal epithelia in many disease states. Although such migration serves as a histological index of disease activity, little is known concerning the molecular events underlying PMN-intestinal epithelial interactions. We have studied chemotactic peptide-driven movement of PMN across cultured monolayers of the human intestinal epithelial cell line T84. Using a transmigration microassay, we show that both the decreased transepithelial resistance (76 +/- 3%) and transmigration (4 +/- 0.6 x 10(5) PMN.cm-2, when PMN applied at 6 x 10(6).cm-2) are largely prevented by MAbs which recognize either subunit of the PMN surface heterodimeric adhesion glycoprotein, CD11b/CD18. In contrast, such PMN-epithelial interactions are unaffected by MAbs recognizing either of the remaining two alpha subunits CD11a or CD11c. PMN from a leukocyte adherence deficiency patient also failed to migrate across epithelial monolayers thus confirming a requirement for CD11/18 integrins. By modifying our microassay, we were able to assess PMN transmigration across T84 monolayers in the physiological direction (which, for technical reasons, has not been studied in epithelia): transmigration was again largely attenuated by MAb to CD18 or CD11b (86 +/- 2% and 73 +/- 3% inhibition, respectively) but was unaffected by MAb to CD11a, CD11c. For standard conditions of PMN density, PMN transmigration in the physiological direction was 5-20 times more efficient than in the routinely studied opposite direction.

An in vivo animal model of gene therapy for leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is an inherited disorder of leukocyte function that is caused by defects in the CD18 gene and is associated with diminished cell surface expression of CD11/CD18 proteins. We have developed an in vivo model for gene therapy of LAD. Recombinant retroviruses were used to transduce a functional human CD18 gene into murine bone marrow cells which were transplanted into lethally irradiated syngeneic recipients. A reliable flow cytometric assay for human CD18 in transplant recipients was developed based on: (a) the availability of human specific CD18 monoclonal antibodies and (b) the observation that human CD18 can form chimeric heterodimers with murine CD11a on the cell surface. Human CD18 was detected on leukocytes in a substantial number of transplant recipients for at least 6 mo suggesting that the gene had been transduced into stem cells. Expression was demonstrated in several lineages of a variety of hematopoietic tissues, but was consistently highest and most frequent in granulocytes. Murine granulocytes demonstrated appropriate posttranscriptional regulation of human CD18 in response to activation of protein kinase C. No apparent untoward effects of human CD18 expression were noted in transplant recipients. These studies suggest a specific strategy for LAD gene therapy that may be effective and safe.

Defective neutrophil and lymphocyte function in leucocyte adhesion deficiency

We report a Chinese girl with the moderate phenotype of leucocyte adhesion deficiency (LAD), presenting with persistent omphalitis and recurrent soft tissue infections. She had subnormal adhesion-dependent neutrophil functions, such as chemotaxis and chemiluminescence response to a particulate stimulant (opsonised zymosan). Despite her adequate humoral response to documented herpes simplex virus type 1, parainfluenza type 2 and adenovirus infection in vivo, there was marked impairment in the generation of plaque-forming cells (PFC) driven by pokeweed mitogen (PWM) in vitro. IgM PFC were less severely affected than IgG and IgA PFC, probably because IgM production is less dependent on T cell help than IgA and IgG production. The patient's B cells and accessory cells had reduced function compared with the control subsets, while helper function of her CD4+ cells was virtually absent in the PWM-driven PFC assay. She also had marked defect in natural killer cell activity. The proliferation of her lymphocytes was normal to several plant lectins, including phytohaemagglutinin, concanavalin A and PWM, but markedly defective to OKT3.

Primary immunodeficiencies: milestones in the history of pediatric immunology

Pediatric immunology is a recent and important branch of pediatrics. Besides development of vaccines, the discovery of primary immunodeficiencies has represented a major contribution in the history of pediatric immunology. Characterization of these disorders as inborn errors of immunity has been crucial for understanding the functional organization and ontogeny of the immune system. Thus, progress in the study of immunodeficiency diseases has contributed to progress in pediatric immunology as a whole. As a result of these advances and a major biotechnology breakthrough, new therapeutic strategies have been devised. The benefits of these strategies extend far beyond the area of immunodeficiencies; they permit better care of infants and give new therapeutic approaches to other inherited disorders.

Molecular mimicry in Candida albicans. Role of an integrin analogue in adhesion of the yeast to human endothelium

Hematogenous infection with the yeast Candida albicans now occurs with increasing frequency in the neonate, the immunocompromised patient, and the hyperglycemic or hyperalimented host. Yeast-phase C. albicans expresses a protein that is antigenically and structurally related to CD11b/CD18, a member of the beta 2 integrins and a well-characterized adhesin for mammalian neutrophils. Both the neutrophil protein and its analogue in C. albicans have an identical affinity for the C3 ligand iC3b, and both proteins are significantly increased in expression at 37 degrees C. Given these several similarities, we therefore studied the role of the integrin analogue on C. albicans in the adhesion of the yeast to human umbilical vein endothelium (HUVE). After growth of C. albicans in 20 mM D-glucose, as opposed to 20 mM L-glutamate, flow cytometric analysis with monoclonal antibodies recognizing the alpha-subunit of CD11b/CD18 demonstrated a 25.0% increase in mean channel fluorescence (range 18.4-31.8%), as well as an increased percentage of yeasts fluorescing (P less than 0.02). This increased intensity of fluorescence, which corresponds to increased expression of the integrin analogue, also correlated with a significant increase of 30-80% in adhesion of glucose-grown C. albicans to HUVE (P less than 0.02). Blockade of the integrin analogue on C. albicans by monoclonal antibodies recognizing adhesive epitopes on neutrophil CD11b/CD18 inhibited glucose-enhanced adhesion of C. albicans to HUVE. Incubation of glucose-grown C. albicans with saturating concentrations of purified human iC3b, the ligand for CD11b/CD18, reduced adhesion of the yeast to HUVE by 49.7%, whereas BSA in equimolar concentration had no effect (P less than 0.001). These results identify a glucose-responsive integrin analogue on C. albicans as one of possibly several cellular structures that mediate adhesion of the yeast to human endothelium.

Ligands "activate" integrin alpha IIb beta 3 (platelet GPIIb-IIIa)

Integrin alpha IIb beta 3 (platelet GPIIb-IIIa) binds fibrinogen via recognition sequences such as Arg-Gly-Asp (RGD). Fibrinogen binding requires agonist activation of platelets, whereas the binding of short synthetic RGD peptides does not. We now find that RGD peptide binding leads to changes in alpha IIb beta 3 that are associated with acquisition of high affinity fibrinogen-binding function (activation) and subsequent platelet aggregation. The structural specificities for peptide activation and for inhibition of ligand binding are similar, indicating that both are consequences of occupancy of the same site(s) on alpha IIb beta 3. Thus, the RGD sequence is a trigger of high affinity ligand binding to alpha IIb beta 3, and certain RGD-mimetics are partial agonists as well as competitive antagonists of integrin function.

Histamine inhibits cell spreading and C3bi receptor clustering and diminishes hydrogen peroxide production by adherent human neutrophils

Cell adherence plays a central role in many host defense mechanisms. Human peripheral blood neutrophils possess cell surface receptors that contribute to cell adherence or detachment. Receptors specific for the C3bi cleavage fragment of the third component of complement (CR3) promote adhesion, whereas histamine receptors promote detachment. In the present study, we tested the ability of histamine to down-regulate the physiological effects of CR3 receptors. Histamine decreased the binding of 51Cr-labeled neutrophils to complement-coated surfaces (C3-coated surfaces) in a dose-dependent fashion. Scanning electron microscopic and optical microscopic observations of neutrophils on C3-coated surfaces revealed polarized or spherical cell morphologies in the absence or presence of histamine, respectively. Histamine inhibited the ability of CR3 to cluster on plasma membranes of neutrophils adherent to C3-coated surfaces as shown by fluorescence microscopy. In addition, histamine diminished but did not abolish the FMLP-stimulated increase in plasma membrane CR3 expression as measured by fluorometry. Histamine did not inhibit the release of marker proteins from specific or gelatinase containing granules by neutrophils in suspension. Histamine also diminished the FMLP-stimulated production of respiratory burst oxidants from cells in suspension or cells allowed to adhere to fibrinogen substrates. We suggest that histamine may modulate selective changes in neutrophil function by diminishing adherence and preventing changes in cell shape following cell activation.

ICAM-1 (CD54): a counter-receptor for Mac-1 (CD11b/CD18)

While the leukocyte integrin lymphocyte function-associated antigen (LFA)-1 has been demonstrated to bind intercellular adhesion molecule (ICAM)-1, results with the related Mac-1 molecule have been controversial. We have used multiple cell binding assays, purified Mac-1 and ICAM-1, and cell lines transfected with Mac-1 and ICAM-1 cDNAs to examine the interaction of ICAM-1 with Mac-1. Stimulated human umbilical vein endothelial cells (HUVECs), which express a high surface density of ICAM-1, bind to immunoaffinity-purified Mac-1 adsorbed to artificial substrates in a manner that is inhibited by mAbs to Mac-1 and ICAM-1. Transfected murine L cells or monkey COS cells expressing human ICAM-1 bind to purified Mac-1 in a specific and dose-dependent manner; the attachment to Mac-1 is more temperature sensitive, lower in avidity, and blocked by a different series of ICAM-1 mAbs when compared to LFA-1. In a reciprocal assay, COS cells cotransfected with the alpha and beta chain cDNAs of Mac-1 or LFA-1 attach to immunoaffinity-purified ICAM-1 substrates; this adhesion is blocked by mAbs to ICAM-1 and Mac-1 or LFA-1. Two color fluorescence cell conjugate experiments show that neutrophils stimulated with fMLP bind to HUVEC stimulated with lipopolysaccharide for 24 h in an ICAM-1-, Mac-1-, and LFA-1-dependent fashion. Because cellular and purified Mac-1 interact with cellular and purified ICAM-1, we conclude that ICAM-1 is a counter receptor for Mac-1 and that this receptor pair is responsible, in part, for the adhesion between stimulated neutrophils and stimulated endothelial cells.

Correction of CD18-deficient lymphocytes by retrovirus-mediated gene transfer

Leukocyte adhesion deficiency (LAD) is an inherited disorder of leukocyte function caused by derangements in CD18 expression. The genetic and functional abnormalities in a lymphocyte cell line from a patient with LAD have been corrected by retrovirus-mediated transduction of a functional CD18 gene. Lymphocytes from patients with LAD were exposed to CD18-expressing retrovirus and enriched for cells that express CD11a and CD18 (LFA-1) on the cell surface. Molecular and functional analyses of these cells revealed (i) one copy of proviral sequence per cell, (ii) viral-directed CD18 RNA that exceeded normal endogenous levels, (iii) normal quantities of CD11a and CD18 protein on the cell surface, and (iv) reconstitution of LFA-1-dependent adhesive function.

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.

Point mutations impairing cell surface expression of the common beta subunit (CD18) in a patient with leukocyte adhesion molecule (Leu-CAM) deficiency

The leukocyte adhesion molecules CD11a/CD18, CD11b/CD18, and CD11c/CD18 (Leu-CAM) are members of the integrin receptor family and mediate crucial adhesion-dependent functions in leukocytes. The molecular basis for their deficient cell surface expression was sought in a patient suffering from severe and recurrent bacterial infections. Previous studies revealed that impaired cell surface expression of Leu-CAM is secondary to heterogeneous structural defects in the common beta subunit (CD18). Cloning and sequencing of complementary DNA encoding for CD18 in this patient revealed two mutant alleles, each representing a point mutation in the coding region of CD18 and resulting in an amino acid substitution. Each mutant allele results in impaired CD18 expression on the cell surface membrane of transfected COS M6 cells. One substitution involves an arginine residue (Arg593----cysteine) that is conserved in the highly homologous fourth cysteine-rich repeats of other mammalian integrin subfamilies. The other substitution involves a lysine residue (Lys196----threonine) located within another highly conserved region in integrins. These data identify crucial residues and regions necessary for normal cell surface expression of CD18 and possibly other integrin beta subunits and define a molecular basis for impaired cell surface expression of CD18 in this patient.

Continuous cell activation is necessary for stable interaction of complement receptor type 3 with its counter-structure in the aggregation response of human neutrophils

Human neutrophils aggregate after stimulation with various stimuli; this response is completely absent in neutrophils from patients with leukocyte adhesion deficiency (LAD). To investigate the cellular requirements of this process a method was used in which neutrophils are separately loaded with hydroethidine (HE) and sulfofluorescein (SFDA), to give them either red fluorescence or green fluorescence. After mixing HE- and SFDA-labeled cells in a ratio of 1:1, the number of double-colored aggregates formed after activation was determined by analysis on a fluorescence-activated cell sorter. In this way, essential information is obtained when cells of different origin are used. The formation of aggregates between neutrophils of an LAD patient and control neutrophils was thus quantified. Because neutrophil aggregation is dependent mostly on the presence of complement receptor type 3 (CR3), which is not present on LAD neutrophils, this result revealed the presence of a counter-structure for CR3 on LAD neutrophils (and hence on normal human neutrophils). In addition to the presence of these proteins on the cell surface, aggregation required continuous cell triggering as indicated by the transient aggregation induced by short-term activation of protein kinase C. This phenomenon was substantiated by the fact that energy depletion caused profound disaggregation. The present study reveals that neutrophil aggregation is a well-controlled process, which needs constant activation of CR3 for a stable interaction with a constitutively expressed counter-structure.

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.

Constitutive and stimulus-induced phosphorylation of CD11/CD18 leukocyte adhesion molecules

The leukocyte CD11/CD18 adhesion molecules (beta 2 integrins) are a family of three heterodimeric glycoproteins each with a distinct alpha subunit (CD11a, b, or c) and a common beta subunit (CD18). CD11/CD18 mediate crucial leukocyte adhesion functions such as chemotaxis, phagocytosis, adhesion to endothelium, aggregation, and cell-mediated cytotoxicity. The enhanced cell adhesion observed upon activation of leukocytes is associated with increased surface membrane expression of CD11/CD18, as well as a qualitative upregulation of CD11/CD18 functions. To elucidate the nature of the qualitative modifications that occur, we examined the phosphorylation status of these molecules in resting human leukocytes and upon activation with PMA or with the chemotactic peptide F-met-leu-phe (FMLP). In unstimulated cells, all three CD11 subunits were found to be constitutively phosphorylated. In contrast, phosphorylation of the common CD18 subunit was minimal. PMA induced rapid and sustained phosphorylation of CD18 that occurred at high stoichiometry, but had only minimal effects on phosphorylation of the associated CD11 subunits. FMLP also induced rapid phosphorylation of CD18, but the effect was of short duration. FMLP-induced phosphorylation of CD18 was not related to its Ca++-mobilizing effect, as CD18 phosphorylation was not observed upon treatment of leukocytes with the Ca++ ionophore, ionomycin. Phosphoamino acid analysis of CD11/CD18 in PMA- or FMLP-treated monocytes revealed a predominance of phosphoserine residues in all CD11/CD18 subunits. A small component of phosphothreonine was present in CD11c and CD18 and a minor component of phosphotyrosine was also detected in CD18 upon leukocyte activation may regulate the adhesion functions mediated by the CD11/CD18 family of molecules.

Monoclonal antibodies for diagnosis of immunodeficiencies

Progress in immunophenotyping is characterized by the availability of monoclonal antibodies and an increased number of clusters of differentiation consisting of reagents with known specificity and defined reactivity patterns. Technical improvements have lead to standardization of immunofluorescence staining procedures and broad application of flow cytometry. These developments have contributed to better diagnosis of immunodeficiencies characterized by the lack of certain lymphocyte subsets or more broadly expressed, functionally important cell-surface molecules. Antibodies valuable for routine immunophenotyping of immunodeficiencies as well as examples of the different antibody groups desirable for immunofluorescence studies are presented. When used in concert with clinical and other laboratory tests, immunophenotyping provides a valuable instrument for differential diagnosis of defects in the immune system. As a consequence, detection of new defects of cell surface antigens and respective cell subpopulations is facilitated and a basis is provided for further study of the genetic and molecular regulatory aspects of immunologic disorders.

History and implications of the neutrophil glycoprotein deficiencies

This review focuses on the initial clinical descriptions and subsequent investigation of the syndrome of recurrent infections associated with neutrophil membrane glycoprotein deficiencies. Characterization of the missing group of three glycoprotein heterodimers and their role in adhesion-related neutrophil function is summarized. Study of the clinical consequences of these genetically determined membrane glycoprotein defects has also contributed to the understanding of the role of normal neutrophils in both host defense and host tissue damage.

Effects of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) on the expression of LFA-1 in the moderate phenotype of leukocyte adhesion deficiency (LAD)

Leukocyte adhesion deficiency (LAD) is a recessive autosomal disease characterized by life-threatening recurrent bacterial infections, associated with defective functions of leukocytes due to deficient membrane expression of leukocyte adhesion glycoproteins. These proteins, LFA-1, Mac-1 (CR3), and p150,95 are alpha 1 beta 1 heterodimers composed of different alpha chains noncovalently associated with a common beta chain. Patients with the severe phenotype of the disease completely lack the three glycoproteins on leukocyte surfaces, while patients with the moderate phenotype can express low levels of leukocyte adhesion proteins (1-10%). We have studied a patient with the moderate phenotype of LAD. Polymorphonuclear functions such as chemotaxis and adherence were altered, natural killer activity was low, and cytotoxic T-lymphocyte activity was abolished. Previous biochemical studies showed a conserved synthesis of both the LFA-1 alpha-chain precursor and the beta-chain precursor with, occasionally, some amount of alpha-beta complexes in the cytosol. beta chain-specific mRNA transcripts of normal size were detected at normal levels in patients' cells. Attempts to increase the transcription of the beta gene by in vitro treatment with TNF-alpha or IFN-gamma were successful but did not result in increased membrane expression of the alpha-beta complexes.

Kinetics and characterization of intercellular adhesion molecule-1 (ICAM-1) expression on keratinocytes in various inflammatory skin lesions and malignant cutaneous lymphomas

The kinetics of expression of the intercellular adhesion molecule-1 (ICAM-1) were studied on keratinocytes in skin biopsy specimens of sensitive persons in whom the haptens were applied in a standardized format for allergic contact dermatitis testing. There was no ICAM-1 expressed on keratinocytes of normal skin; ICAM-1 was induced as early as 4 hours after the application of the patch in some subjects. By 48 hours after the application of the patch, all specimens contained ICAM-1-positive keratinocytes. This was concurrent with a heavy mononuclear cell dermal infiltrate and maximum clinical manifestations. Expression of human lymphocyte antigen (HLA)-DR or other inducible surface proteins on keratinocytes under these conditions was much less frequent. When specimens from primary irritant dermatitis were used, only 1 of 14 cases had keratinocytes expressing ICAM-1 at 48 hours, the time of maximum clinical manifestation. Among benign inflammatory lesions, most cases resembled the allergic patch test specimens in that ICAM-1 was expressed to a large degree on keratinocytes. Again, the expression of HLA-DR was variable. Malignant skin lesions, on the other hand, were much less consistent and generally lower in terms of ICAM-1 expression on keratinocytes. Furthermore, in contrast to the benign cutaneous conditions, some malignant skin lesions contained keratinocytes that expressed class II antigens or other inducible surface proteins in the absence of ICAM-1. These data suggest that ICAM-1 plays a role in the specific immune response by facilitating either antigen presentation or lymphocytic infiltration.

Intercellular adhesion molecule-I (ICAM-I) expression correlated to inflammation

The presence of intercellular adhesion molecule-I (ICAM-I) on keratinocytes of psoriatic skin lesions before and during 8-methoxapsoralen and UVA light (PUVA) treatment was studied. ICAM-I was expressed on the keratinocytes in biopsies of the skin lesions of five patients with psoriasis. The patients who responded to PUVA treatment had a concurrent reduction of ICAM-I expression on the keratinocytes with a reduction of the number of cells in the mononuclear cellular infiltrate and a lessening of the severity of the disease. Patients who went into remission during therapy and then relapsed showed an increase in ICAM-I expression on keratinocytes with an increase in the number of cells in the mononuclear cell infiltrate and an increase in the severity of the disease. HLA-DR expression on keratinocytes was variable during treatment and showed no strong correlation with disease severity.

Histiocytic differentiation in benign and malignant bone tumors

In this study fresh frozen tissue samples of benign osseous tumors (five non-osteogenic fibromas, one fibrous dysplasia, one chondromyxoidfibroma), tumors of uncertain biological behaviour (eight cases of histiocytosis X, two giant-cell tumors), and of malignant intraosseous tumors (two malignant fibrous histiocytomas, two malignant histiocytosis, four osteosarcomas, one chondrosarcoma and two Ewing sarcomas) were studied with a panel of monoclonal antibodies reactive with monocyte/macrophages and various types of dendritic cells. In addition, tumors were further defined with a broad spectrum of antibodies against filamentous proteins and lymphocyte differentiation antigens. The specimens were stained with a triple-layer immunoalkaline phosphatase protocol. Tumors stained with these antibodies could be roughly divided into two groups. The first group comprised tumors with one predominant cell population reactive with one particular monoclonal antibody. In this group, cases of histiocytosis X were found to be consistently labelled with CD-1 antibodies. The giant-cell tumors showed a very homogeneous staining with certain monocyte/macrophage antibodies (Ki-M8). Nevertheless, even in these tumors, heterogeneity was demonstrated by the occurrence of cells with monocytic differentiation in histiocytosis X and conversely by the occurrence of cells with differentiation antigens of the dendritic cell system in giant-cell tumors. An exception has to be made for the two cases of malignant histiocytosis examined. These tumors were selectively labelled with antibodies against monocyte/macrophages (Ki-M8, IOM-1). The second group comprised tumors showing a high degree of heterogeneity demonstrated by the varying amounts of tumor cells reacting with the applied markers of the monocyte/macrophage and dendritic cell systems. In most cases it was difficult to ascribe labelled cells to the tumor cell population as opposed to an "innocent bystander" inflammatory cell population. This distinction was especially difficult in malignant fibrous histiocytomas underlining the current concept that these tumors are of primitive mesenchymal rather than true histiocytic origin.

The phenotype of human placental macrophages and its variation with gestational age

The antigenic phenotype of human villous stromal macrophages (M phi s) from first and third trimester placentas was analyzed using a large number of monoclonal antibodies (MAbs) to monocyte (Mo)/M phi-associated cell membrane determinants. The purpose of this study was to investigate M phi phenotypic heterogeneity to create a database for the correlation of M phi phenotype with specific immunologic functions. The results showed that villous stromal mononuclear cells express many cell surface antigens found on Mo and M phi s and that they are morphologically diverse, ranging in appearance from classic Hofbauer cells to spindle-shaped cells with long cytoplasmic processes. Villous stromal M phi s were the numerically dominant cell type in this structure and exhibited some major phenotypic differences from M phi s in other tissues. Comparison of first- and third-trimester placentas revealed variation in antigen expression with increasing gestational age, in particular of class II major histocompatibility complex (MHC) determinants: HLA-DR and HLA-DP antigen density was low on first-trimester villous M phi s and much higher on third-trimester M phi s while HLA-DQ was undetectable in the first trimester but present on cells in third trimester placentas. The CD1 (T6) antigen, found on Langerhans (LH) cells and cortical thymocytes, was detected on villous M phi s by two thirds of the MAbs directed against different epitopes on this determinant. Furthermore, comparison with similar studies of lymphoid tissues showed that villous M phi s and dendritic cells share the expression of a number of other cell surface antigens. Finally, it was shown that M phi s in first- and third-trimester villi exhibit strong reactivity with MAbs (Leu 3a,b) to the CD4 antigen that serves as the receptor for the human immunodeficiency virus (HIV), suggesting that these cells may be a portal of entry or reservoir for this virus in the fetuses of pregnant, HIV+ women.

Neutral-red uptake and expression of monocytic antigens in amniotic-fluid mononuclear phagocytes: evaluation of a novel approach for prenatal diagnosis of neural-tube defects

In cases of fetal neural-tube defects macrophages are present in the amniotic fluid. We found that these viable phagocytic cells take up neutral-red and are easily identified as "red cells" by microscopic examination. This method is suitable for the rapid identification and counting of amniotic-fluid macrophages in suspension. We have studied 298 amniotic fluid samples. In the 226 normal cases studied, 0 to 1,200 macrophages per milliliter amniotic fluid have been found. In contrast, we found 1,250 to 99,000 macrophages per milliliter amniotic fluid in our 70 open neural tube defect (ONTD) cases. Statistical evaluation was performed to estimate the normal and pathologic ranges. Specificity and sensitivity of the neutral-red test and predictive value of positive and negative results have been calculated and presented in comparison with alpha-fetoprotein (AFP) determinations and ultrasonic methods. In 5 cases of anencephaly and 7 normal cases amniotic fluid cells were studied by immunocytochemistry: mononuclear cells present in the abnormal cases showed intense immunoreactivity for the Mo1 and Mo2 surface antigens of the phagocytic cell lineage.

Heterogeneity in the molecular defect leading to the leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is a recessive autosomal disease characterized by life-threatening recurrent bacterial infections, by defective functions of leukocytes and by deficient membrane expression of leukocyte adhesion glycoproteins. These proteins, LFA-1, Mac-1 and p150,95, are alpha 1/beta 1 heterodimers composed of different alpha chains and of a common beta chain. Patients with the severe phenotype of the disease completely lack the three glycoproteins on cell surface. Previous studies showed a conserved synthesis of the LFA-1 alpha chain precursor in cytosol of patients' cells and an inconstant presence of the beta chain precursor. When present, precursors are in free form and not associated to alpha/beta complexes in the cells of patients with the severe phenotype. The availability of the beta chain cDNA probe allowed us to examine the beta chain gene expression in the lymphoblastoid cell lines of 4 patients. On the basis of the results obtained both at protein and RNA levels we can distinguish 3 types of mutations characterized by (a) barely detectable beta subunit messenger RNA and undetectable beta precursor, (b) decreased level of beta subunit mRNA and undetectable beta precursor and (c) normal beta subunit mRNA level and detectable beta precursor of normal size.

Absence of complement receptor type 3 and lymphocyte function antigen 1 causing deficient phagocyte and lymphocyte functions

We describe a patient with delayed umbilical cord detachment, recurrent bacterial infections, and inability to form pus, despite persistent leucocytosis. Immunofluorescence studies with specific monoclonal antibodies showed a severe deficiency in the expression of alpha-chains of the receptor for the C3bi fragment of C3, complement receptor type 3, and the lymphocyte function antigen 1 molecule, found on neutrophil, monocyte and lymphocyte membranes. These membrane antigen defects were responsible for abnormalities in adhesive cell functions. Polymorphonuclear leucocytes demonstrated a markedly reduced chemiluminescence response as well as an impaired nitroblue tetrazolium test and superoxide generation to a particulate stimulus (zymosan), while the responses to a soluble stimulus (phorbol myristate acetate) were normal. In addition, random migration und chemotactic response to zymosan-activated serum were impaired. The lymphocytes demonstrated abolished natural killer cell cytotoxicity as well as abnormal humoral immunity and a lack of antibody response to pertussis and tetanus antigens.

Severe hypoplasia of lymphoid tissues in Mo1 deficiency

A lymph node was examined from a 4-year-old female child with documented "Mo1" (CR3) deficiency. There was hypoplasia of the lymph node, with small, poorly delineated germinal centers and overall lymphopenia. Retrospective analysis of the clinical course of a decreased elder sister of the index patient indicated that the elder sister probably also had "Mo1" deficiency. Review of findings at autopsy revealed severe hypoplasia of all lymphoid organs with lymphopenia. Our observations suggest that lymphoid tissue hypoplasia may be a feature of CR3 deficiency and is likely a result of the defective lymphocyte adherence functions to endothelium associated with absent lymphocyte function-associated antigen (LFA-1).

Amino acid sequence of the alpha subunit of human leukocyte adhesion receptor Mo1 (complement receptor type 3)

Mo1 (complement receptor type 3, CR3; CD11b/CD18) is an adhesion-promoting human leukocyte surface membrane heterodimer (alpha subunit 155 kD [CD11b] noncovalently linked to a beta subunit of 95 kD [CD18]). The complete amino acid sequence deduced from cDNA of the human alpha subunit is reported. The protein consists of 1,136 amino acids with a long amino-terminal extracytoplasmic domain, a 26-amino acid hydrophobic transmembrane segment, and a 19-carboxyl-terminal cytoplasmic domain. The extracytoplasmic region has three putative Ca2+-binding domains with good homology and one with weak homology to the "lock washer" Ca2+-binding consensus sequence. These metal-binding domains explain the divalent cation-dependent functions mediated by Mo1. The alpha subunit is highly homologous to the alpha subunit of leukocyte p150,95 and to a lesser extent, to the alpha subunit of other "integrin" receptors such as fibronectin, vitronectin, and platelet IIb/IIIa receptors in humans and position-specific antigen-2 (PS2) in Drosophila. Mo1 alpha, like p150, contains a unique 187-amino acid stretch NH2-terminal to the metal-binding domains. This region could be involved in some of the specific functions mediated by these leukocyte glycoproteins.

Studies on phagocytosis of unopsonized rabbit erythrocytes by human monocytes

Monolayers of freshly isolated human monocytes are known to ingest particulate activators of the human alternative complement pathway. The ingestion of rabbit erythrocytes, ER, by human monocytes in serum-free medium was studied. The process is Mg2+-dependent and optimum phagocytic activity was obtained at approximately 20 mM MgCl2. Preincubation of mononuclear leukocytes increased the number of monocytes ingesting ER by at least twofold and this involved de novo protein synthesis, as evidenced by inhibition with cycloheximide. However, preincubation of the mononuclear leukocytes for longer periods (greater than 4 hr) caused a decrease in the percentage of ingesting monocytes. No inhibition of ingestion of ER was observed by cobra venom factor (CVF) or F(ab')2 rabbit anti-human C3 of F(ab')2 murine monoclonal anti-human Bb, known to inhibit C3 convertase activity. The ingestion was also not inhibited by (a) rabbit anti-human CR1, (b) OKM1 or anti-MO1, two monoclonal anti-CR3 antibodies, (c) goat anti-human IgG Fc receptor, or (d) mannan, a competitive inhibitor of ligand uptake by the mannosyl-fucosyl receptor (MFR). In contrast, ingestion was inhibited by glucan particles of yeast.

Increased adherence of human granulocytes to herpes simplex virus type 1 infected endothelial cells

We studied the interaction of human polymorphonuclear leukocytes (PMNs) with umbilical vein endothelial cells infected with herpes simplex virus (HSV) type 1. PMNs labeled with 51Cr were added to endothelial monolayers at varying times after infection and their adherence assessed 1 h later. Granulocyte adherence (GA) to uninfected cells averaged 26.5 +/- 1.9%. Increased adherence began 6 h postinfection and rose to a maximum at 20 to 24 h. HSV-1 glycoproteins seemed to mediate the increase in GA: tunicamycin treatment of infected monolayers for 18 h abolished the increased GA as did incubation of infected cells with F(ab')2 fragments prepared from human antiserum containing HSV-1 antibody.

Molecular cloning of the alpha subunit of human and guinea pig leukocyte adhesion glycoprotein Mo1: chromosomal localization and homology to the alpha subunits of integrins

The cell-surface glycoprotein Mo1 is a member of the family of leukocyte cell adhesion molecules (Leu-CAMs) that includes lymphocyte function-associated antigen 1 (LFA-1) and p150,95. Each Leu-CAM is a heterodimer with a distinct alpha subunit noncovalently associated with a common beta subunit. Leu-CAMs play crucial roles in cell-cell and cell-matrix interactions. We describe the isolation and analysis of two partial cDNA clones encoding the alpha subunit of the Leu-CAM Mo1 in humans and guinea pigs. A monoclonal antibody directed against an epitope in the carboxyl-terminal portion of the guinea pig alpha chain was used for immunoscreening a lambda gt11 expression library. The sequence of a 378-base-pair insert from one immunoreactive clone revealed a single continuous open reading frame encoding 126 amino acids including a 26-amino acid tryptic peptide isolated from the purified guinea pig alpha subunit. A cDNA clone of identical size was isolated from a human monocyte/lymphocyte cDNA library by using the guinea pig clone as a probe. The human clone also encoded a 126-amino acid peptide including the sequence of an additional tryptic peptide present in purified human Mo1 alpha chain. RNA gel blots revealed that mature Mo1 alpha chain mRNA is approximately 5 kilobases in guinea pigs and humans. Southern analysis of DNA from hamster-human hybrids localized the human Mo1 alpha chain to chromosome 16, which has been shown to contain the gene for the alpha chain of lymphocyte function-associated antigen 1. A comparison of the Mo1 alpha chain coding region revealed significant homologies with carboxyl-terminal portions of the alpha subunits of fibronectin, vitronectin, and platelet IIb/IIIa receptors. These data suggest that the alpha subunits of Leu-CAMs evolved by gene duplication from a common ancestral gene and strengthen the hypothesis that the alpha subunits of these heterodimeric cell adhesion molecules on myeloid and lymphoid cells, platelets, and fibroblasts are evolutionary related.

Reduction of experimental canine myocardial reperfusion injury by a monoclonal antibody (anti-Mo1, anti-CD11b) that inhibits leukocyte adhesion

A monoclonal antibody (904) that binds to a leukocyte cell adhesion-promoting glycoprotein, (Mo1; CD11b/CD18) was administered (1 mg/kg, iv.) to open chest anesthetized dogs 45 min after the induction of regional myocardial ischemia. Ischemia was produced by occluding the left circumflex coronary artery (LCX) for 90 min and then reperfusing for 6 h. There was no difference between control and antibody treated groups with respect to arterial blood pressure, heart rate, or LCX blood flow. Administration of antibody produced no observable effect on circulating neutrophil counts, suggesting that antibody-bound neutrophils were not cleared from the circulation. The mean size of myocardial infarct expressed as percentage of the area at risk of infarction that resulted was reduced by 46% with anti-Mo1 treatment (25.8 +/- 4.7%, n = 8) compared to control (47.6 +/- 5.7%, n = 8; P less than 0.01). The area at risk of infarction was similar between groups. Circulating (serum) antibody excess was confirmed in all 8 anti-Mo1 treated dogs by immunofluorescence analysis. Analysis of ST segment elevation on the electrocardiogram as an indicator of the severity of ischemia suggests that the anti-Mo1 reduces infarct size independent of the severity of ischemia. An additional group of dogs (n = 5) was tested with a control monoclonal antibody of the same subtype (murine IgG1) and was found to produce no significant reduction in myocardial infarct size. Accumulation of neutrophils within the myocardium was significantly attenuated with 904 treatment when analyzed by histological methods. These data demonstrate that administration of anti-Mo1 monoclonal antibody after the induction of regional myocardial ischemia results in reduced myocardial reperfusion injury as measured by ultimate infarct size.

Neutrophil C3bi receptors: formation of membrane clusters during cell triggering requires intracellular granules

Video-intensification fluorescence microscopy has been used to study the cell surface distribution of the complement receptor (CR) for C3bi (CR3) on human neutrophils. Fluorescein- or rhodamine-labeled monoclonal IgG or Fab fragments of antireceptor antibody were used as probes of receptor localization. C3bi receptors are uniformly distributed on untreated cells. Glass coverslips were coated with lipopolysaccharide (LPS) and serum was added; the serum deposits complement components, including C3bi, on the surface. When neutrophils were adherent to these coverslips, receptors were found in large clusters, and a fraction of the fluorescence remained uniform. Double-labeling studies were conducted by first labeling with anti-CR3 followed by attachment to LPS/serum-treated slides. This, in turn, was followed by labeling with the antibody conjugated to a second fluorophore. These studies revealed that the CR3 clusters were predominantly new antigenic sites exposed after attachment to the LPS/serum-treated slides. To determine the contribution of granule-associated CR3, we have studied neutrophils defective in receptor up-regulation, neutrophil cytoplasts, and a stimulator of granule release, A23187. Neutrophils from a patient with specific granule deficiency were found to be defective in granular CR3 and did not form clusters on C3-modified surfaces. The patient's neutrophils were defective in CR3 up-regulation and enzyme release as shown by fluorescence flow cytometry and gelatinase release, respectively. Cytoplasts also failed to show CR3 clusters on LPS/serum-treated coverslips. Furthermore, neutrophils treated with A23187 demonstrated numerous CR3 clusters. We suggest that formation of CR3 membrane domains during immune recognition requires the participation of intracellular granules. We speculate that these domains are formed by fusion of CR3-bearing granules at local sites of adhesion.

Human spleen contains phenotypic subsets of macrophages and dendritic cells that occupy discrete microanatomic locations

Macrophages (M phi s) are an important component of the immune response and mediate numerous other functions. Phenotypic and functional subsets of circulating monocytes have been described, but few similar studies have analyzed M phi s in human tissues. By use of immunohistochemical techniques and a large number of monoclonal antibodies, the presence and distribution of phenotypic subpopulations of M phi s and dendritic cells in human spleen were assessed. The results of this study show that different subsets of M phi s and dendritic cells are present in the spleen and that some of these occupy discrete microanatomic locations. In the red pulp (RP) certain groups of antigens are expressed by different proportions of uniformly distributed M phi s in the cords. On the other hand, some antigens are present on M phi s that form clusters of variable size within the red pulp. M phi s in the splenic marginal zone (MZ) share some antigens with red pulp M phi s, but in addition express CR3, Mo-2, 61D3, and 63D3. These antigens are found on only a few RP M phi s. MZ cells expressing one antigen shared with RP M phi s (Leu-3a,b) and one present largely on the MZ cells (63D3) form clusters around small vessels; these structures resemble the so-called splenic ellipsoids that may play a role in the trapping of circulating antigens. Phagocytic M phi s (tingible body M phi s) of the white pulp follicular germinal centers were also shown to differ from RP and MZ cels with respect to the expression of the antigens detected by anti-FcR, Leu-M3, Mo-2, 25F9, and anti-CR3. The unique topographical and surface antigenic features of dendritic cells were confirmed by this study. Furthermore, these cells were found to share a number of antigens with RP, MZ, and white pulp M phi s, which suggests that they may be derived from a common progenitor. The presence of phenotypic subpopulations and variation in distribution among human splenic phagocytic cells and dendritic cells may be indicative of functional specialization.

Comparison of blocking effects of monoclonal antibodies anti-MO1-alpha and anti-LFA1-alpha on human neutrophil functions

In order to analyse the role of LFA1 and MO1 on neutrophil functions, the blocking effects of two monoclonal antibodies (MAb), one (anti-MO1) recognizing an epitope of the MO1-alpha chain and the other (25.31) an epitope of the LFA1-alpha chain, were measured. Adherence of 51Cr-labelled control neutrophils was 66 + 8% (mean +/- 1 SD) on plastic nuclon plates; this figure decreased to 33 +/- 5% and 23 +/- 6% of control adherence when the neutrophils had been pretreated with anti-LFA1-alpha (anti-alpha L) and anti-MO1-alpha (anti-alpha M), respectively. On another support (plastic culture chambers), 84 +/- 6% of control neutrophils adhered and the adherence of neutrophils pretreated with anti-alpha L or anti-alpha M was 10% and 43% of the control figure, respectively. These results show that adherence of neutrophils is dependent upon the plastic used. Moreover, inhibition of adhesion by the two MAbs was also dependent upon the support used for the assay, suggesting that MO1 and LFA1 may be surface proteins with different specificities. Both antigens capped upon adhesion, while they were randomly distributed in resting neutrophils. Anti-alpha L inhibited (congruent to 50%) locomotion more than did anti-alpha M (congruent to 25%), without altering chemoattractant-induced shape changes. These results suggest that the two MAbs inhibit chemokinesis but not chemotaxis. Many other adherence-associated functions, such as ingestion of opsonized Klebsiella pneumoniae, and cytotoxicity towards K/562 cells were decreased more by anti-alpha L than by anti-alpha M. In contrast, chemiluminescence and iodination induced by opsonized zymosan were inhibited more by anti-alpha M than by anti-alpha L. Degranulation induced by zymosan or opsonized zymosan was altered by anti-alpha M only, and this alteration involved azurophilic and not specific granules. Chemiluminescence induced by phorbol myristate acetate was inhibited to a greater extent by anti-alpha M than by anti-alpha L, while degranulation induced by phorbol myristate acetate was not altered by either of the two Mabs.

Human breast cancer cells share antigens with the myeloid monocyte lineage

We have examined the expression of several myeloid cell associated antigens, some of which are involved in myelomonocyte adhesion, in seven well characterized human breast cancer cell lines, since common properties of adhesiveness and migration are found in haemopoietic cells and epithelial cancer cells. Five of these cell lines were of metastatic origin and two were derived from primary breast carcinoma. Antigenic expression was evaluated by immunofluorescence (IF), flow cytometry (FCM), radioimmunoassay on live cells (RIA) and immunoperoxidase staining. None of these cell lines expressed T or B lymphoid specific antigens. Myeloid antigens My4, MO1, and MOF11 (derived from the hybridization of mouse X63 - Ag8 cells with spleen cells from Balb/c mice immunized with purified human monocytes) were expressed in the 7 cell lines. Leu M1, Leu M3, My9, and MO2 antigens were expressed in some of the cell lines. Leu M2 and My7 antigens were not expressed or at very low levels. The expression of these myeloid antigens was also tested by immunoperoxidase staining, and found on frozen sections of normal mammary gland, fibroadenoma of the breast, primary breast cancer, and lymph node and skin metastases of breast tumours. This common expression in epithelial breast cells and in myeloid cells might be related to common biological functions such as interaction with extracellular matrix which precedes cell migration, a normal function of macrophages and an abnormal function expressed or amplified in human cancer epithelial cells.

Expression of CR1 and CR2 complement receptors following Epstein-Barr virus infection of Burkitt's lymphoma cell lines

Epstein-Barr virus (EBV) infection of human B lymphocytes involves a specific receptor closely associated with, or identical to, the C3d complement receptor, CR2. Thus, 25 out of 29 EBV-positive Burkitt's lymphoma (BL) cell lines but none of 15 EBV-negative BL lines were found to express C3 receptors. Furthermore, in vitro infection with EBV of six EBV-negative cell lines resulted in the expression of C3 receptors in association with that of EBV-determined nuclear antigen (EBNA). Rosette assays using erythrocytes coated with human C3b, C3bi, and C3d, inhibition of rosette formation with anti-receptor antibodies, and flow cytometry analysis of stained cells demonstrated that EBV-converted lines expressed C3b and C3d receptors, CR1 and CR2. Anti-receptor antibodies recognized an average of 40,700 anti-CR1 and 140,000 anti-CR2 binding sites on an EBV-converted line (BL41/B95), whereas no specific binding occurred on the corresponding EBV-negative (BL41) cells. Because CR1 and CR2 are involved in B-cell proliferation and/or differentiation, enhanced expression of C3 receptors following the interaction between EBV and B cells and/or subsequent infection of the cells by EBV may provide a basis for positive control of B lymphocyte proliferation by EBV.

Polymorphism of lymphocyte function-associated antigen-1 demonstrated by a lupus patient's alloantiserum

We have found a human serum, E27, obtained from a multiply transfused patient with systemic lupus erythematosus, which immunoprecipitates the lymphocyte function associated antigen-1 (LFA-1). The immunoprecipitated molecules were identified as the LFA-1 alpha and beta chains by their comigration on SDS-PAGE, two-dimensional SDS-PAGE, and by sequential clearance experiments. Serum E27 did not immunoprecipitate LFA-1 from autologous cells, though LFA-1 molecules were present. In contrast, serum E27 immunoprecipitated LFA-1 from most but not all normal donor lymphocytes. Thus, serum E27 defines two serological phenotypes of LFA-1. 95% of normal individuals tested exhibited the LFA-1 phenotype precipitated by serum E27. Serum E27 appears to be directed at determinants of the LFA-1 alpha-chain and not the beta-chain since it immunoprecipitated LFA-1 molecules but not the Mac-1 molecules. Additional evidence for the alpha chain specificity was provided by immunoprecipitation of mouse-human heterohybridoma cells. LFA-1 was immunoprecipitated by serum E27 from mouse-human heterohybridoma cells expressing the human alpha-chain, not from a hybrid cell line expressing the human beta-chain. Together these findings demonstrate an antigenic polymorphism of the human LFA-1 alpha-chain molecule.

Membrane glycoproteins of human polymorphonuclear leukocytes that act as receptors for mannose-specific Escherichia coli

Type 1 fimbriated (mannose-specific) Escherichia coli cells bind to mannose residues on human polymorphonuclear leukocytes (PMN); this leads to phagocytosis of the bacteria. To identify the mannose-containing receptors on the PMN, the cells were surface labeled with 125I and lysed in 0.5% Nonidet P-40, and the lysate was fractionated by affinity chromatography on a column of Sepharose-bound fimbriae. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of the material eluted from the column with 500 mM methyl-alpha-mannoside revealed two radioactive bands of Mr 70,000 to 80,000 (gp70-80) and 100,000 (gp100). Another weak band of Mr 150,000 (gp150) was observed after prolonged exposure of the gel. Upon blotting of the glycoproteins separated by polyacrylamide gel electrophoresis and overlaying of the blots with concanavalin A, gp150 appeared as the major band. Membrane preparations of the PMN were enriched in gp70-80, gp100, and gp150, in comparison with the cell homogenates, further suggesting that these glycoproteins are surface components. Fractionation of the membrane preparations on the immobilized fimbriae followed by concanavalin A overlay of blots of the methyl-alpha-mannoside-eluted material revealed that gp150 was the major component in this fraction. The eluted fraction, obtained from a cell lysate (4.4 micrograms/ml), inhibited by 70% the agglutination of yeasts by the intact bacteria. Our results suggest that the three surface glycoproteins isolated by us serve as receptors for mannose-specific E. coli on PMN and may be involved in the lectin-mediated phagocytosis of the bacteria.

LFA-1 beta-chain synthesis and degradation in patients with leukocyte-adhesive proteins deficiency

The defective membrane expression of the adhesive protein family (LFA-1, Mo1 and p150,93) on leukocytes from certain patients with recurrent bacterial infections was shown to be secondary to the absence of synthesis of mature beta chain that is common to all three antigens (Springer et al., 1984, Lisowska-Grospierre et al., 1986). In all patients, studies of beta-chain biosynthesis that lead to this conclusion were performed using the monoclonal anti-beta chain antibody to isolate the beta subunit. Since this antibody detects the mature form of beta chain only, the potential presence of a precursor or of an abnormal beta chain in the patient's cells could not be tested. The availability of the polyclonal antibody to the purified beta subunit allowed us to re-examine the biosynthesis of the LFA-1 subunits in 3 affected children. In all 3 patients, the absence of membrane expression of the LFA-1, CR3 and p150,95 proteins was confirmed. The LFA-1 alpha-chain precursor of 170 kDa was detected in the lysates of PHA blasts of two children, but was not detected in the third. The beta-chain precursor of 85 kDa was isolated by the polyclonal anti-beta chain antiserum from the cytoplasm of phytohemagglutinin and Epstein-Barr virus-induced blasts of one patient. The same antibody precipitated some peptides of smaller mol. wt. from the cell lysates of 2 other patients. These results suggest that in this disorder the membrane nonexpression of the adhesive proteins is probably due to the structural abnormality of beta chain which, although synthesized, is rapidly degradated.