Human leukocyte function-associated antigens on lympho-hemopoietic precursor cells

Fetal haemopoietic cells display enhanced migration across endothelium

Fetal haemopoietic cells continually circulate and migrate into tissues, and thus may have specialized homing capabilities. In this study we investigated the in vitro features of haemopoietic cells in fetal blood and liver which are relevant to homing and engraftment. Fetal cells were examined for long-term culture-initiating cell (LTC-IC) and progenitor content, adhesion molecule expression, cell cycle behaviour and transendothelial migratory activity. The LTC-IC content of fetal CD34+ cells is similar to that of CD34+ cells from cord and adult mobilized blood. In contrast to adult and cord blood CD34+ cells, fetal CD34+ cells were actively cycling (11.0 +/- 1.7% and 28 +/- 1.1% of fetal blood and liver CD34+ cells, respectively, in S+G2M, P < 0.001, compared with cord and adult cells). The striking finding was that fetal haemopoietic cells (both LTC-ICs and committed progenitors) displayed significantly higher levels of migration across endothelium (P < 0.05 compared with cord, P < 0.01 compared with adult blood and bone marrow CD34+ cells), which were further increased by chemokines and growth factors. The superior migratory activity of fetal haemopoietic cells may underlie a more efficient homing ability, in keeping with their physiological role.

Mechanisms underlying hematopoietic stem cell mobilization induced by the CXC chemokine interleukin-8

The CXC chemokine interleukin-8 induces rapid mobilization of hematopoietic progenitor cells in mice and monkeys. Antibodies against the beta 2-integrin leukocyte function-associated antigen-1 completely blocked interleukin-8-induced mobilization. This was not due to a direct effect on the hematopoietic progenitor cells, as leukocyte function-associated antigen-1 was found not to be expressed on hematopoietic progenitor cells. Additional experiments showed that interleukin-8 induces the rapid release of the metalloproteinase gelatinase B, concurrent with the mobilization of hematopoietic progenitor cells. Mobilization could be completely prevented by anti-gelatinase B antibodies. Because neutrophils express leukocyte function-associated antigen-1 and high affinity interleukin-8 receptors, and release gelatinase B upon stimulation with interleukin-8, we hypothesized that neutrophils are key mediators in interleukin-8-induced stem cell mobilization. Further studies showed that mobilization by interleukin-8 was completely absent in mice rendered neutropenic with anti-granulocytic antibodies. Taken together, these data are consistent with an essential role for neutrophils in interleukin-8-induced stem cell mobilization.

Murine Hematopoietic Progenitor Cells With Colony-Forming or Radioprotective Capacity Lack Expression of the β2-Integrin LFA-1

Recently, we have demonstrated that antibodies that block the function of the β2-integrin leukocyte function-associated antigen-1 (LFA-1) completely abrogate the rapid mobilization of hematopoietic progenitor cells (HPC) with colony-forming and radioprotective capacity induced by interleukin-8 (IL-8) in mice. These findings suggested a direct inhibitory effect of these antibodies on LFA-1–mediated transmigration of stem cells through the bone marrow endothelium. Therefore, we studied the expression and functional role of LFA-1 on murine HPC in vitro and in vivo. In steady state bone marrow ± 50% of the mononuclear cells (MNC) were LFA-1neg. Cultures of sorted cells, supplemented with granulocyte colony-stimulating factor (G-CSF)/granulocyte-macrophage colony-stimulating factor (GM-CSF)/IL-1/IL-3/IL-6/stem cell factor (SCF) and erythropoietin (EPO) indicated that the LFA-1neg fraction contained the majority of the colony-forming cells (CFCs) (LFA-1neg 183 ± 62/7,500 cells v LFA-1pos 29 ± 17/7,500 cells,P &lt; .001). We found that the radioprotective capacity resided almost exclusively in the LFA-1neg cell fraction, the radioprotection rate after transplantation of 103, 3 × 103, 104, and 3 × 104 cells being 63%, 90%, 100%, and 100% respectively. Hardly any radioprotection was obtained from LFA-1pos cells. Similarly, in cytokine (IL-8 and G-CSF)–mobilized blood, the LFA-1neg fraction, which comprised 5% to 10% of the MNC, contained the majority of the colony-forming cells, as well as almost all cells with radioprotective capacity. Subsequently, primitive bone marrow-derived HPC, represented by Wheat-germ-agglutinin (WGA)+/Lineage (Lin)−/Rhodamine (Rho)− sorted cells, were examined. More than 95% of the Rho− cells were LFA-1neg. Cultures of sorted cells showed that the LFA-1neg fraction contained all CFU. Transplantation of 150 Rho− LFA-1neg or up to 600 Rho−LFA-1pos cells protected 100% and 0% of lethally irradiated recipient mice, respectively. These results show that primitive murine HPC in steady-state bone marrow and of cytokine-mobilized blood do not express LFA-1.

Murine Hematopoietic Progenitor Cells With Colony-Forming or Radioprotective Capacity Lack Expression of the β2-Integrin LFA-1

Recently, we have demonstrated that antibodies that block the function of the β2-integrin leukocyte function-associated antigen-1 (LFA-1) completely abrogate the rapid mobilization of hematopoietic progenitor cells (HPC) with colony-forming and radioprotective capacity induced by interleukin-8 (IL-8) in mice. These findings suggested a direct inhibitory effect of these antibodies on LFA-1–mediated transmigration of stem cells through the bone marrow endothelium. Therefore, we studied the expression and functional role of LFA-1 on murine HPC in vitro and in vivo. In steady state bone marrow ± 50% of the mononuclear cells (MNC) were LFA-1neg. Cultures of sorted cells, supplemented with granulocyte colony-stimulating factor (G-CSF)/granulocyte-macrophage colony-stimulating factor (GM-CSF)/IL-1/IL-3/IL-6/stem cell factor (SCF) and erythropoietin (EPO) indicated that the LFA-1neg fraction contained the majority of the colony-forming cells (CFCs) (LFA-1neg 183 ± 62/7,500 cells v LFA-1pos 29 ± 17/7,500 cells,P < .001). We found that the radioprotective capacity resided almost exclusively in the LFA-1neg cell fraction, the radioprotection rate after transplantation of 103, 3 × 103, 104, and 3 × 104 cells being 63%, 90%, 100%, and 100% respectively. Hardly any radioprotection was obtained from LFA-1pos cells. Similarly, in cytokine (IL-8 and G-CSF)–mobilized blood, the LFA-1neg fraction, which comprised 5% to 10% of the MNC, contained the majority of the colony-forming cells, as well as almost all cells with radioprotective capacity. Subsequently, primitive bone marrow-derived HPC, represented by Wheat-germ-agglutinin (WGA)+/Lineage (Lin)−/Rhodamine (Rho)− sorted cells, were examined. More than 95% of the Rho− cells were LFA-1neg. Cultures of sorted cells showed that the LFA-1neg fraction contained all CFU. Transplantation of 150 Rho− LFA-1neg or up to 600 Rho−LFA-1pos cells protected 100% and 0% of lethally irradiated recipient mice, respectively. These results show that primitive murine HPC in steady-state bone marrow and of cytokine-mobilized blood do not express LFA-1.

Circulating promyelocytes and low levels of CD16 expression on polymorphonuclear leukocytes accompany early-onset periodontitis

Early-onset periodontitis (EOP) is characterized by rapidly progressive alveolar bone loss, chemotactic defects of neutrophils, and significant familial aggregation. We found immature myeloid lineage cells, defined as promyelocytes, in the peripheral blood in patients with EOP. A hematological examination of peripheral blood cells showed normal reference values regarding cell proportions. Flow cytometry revealed significantly lower expression of CD16, a glycosylphosphatidylinositol (GPI)-anchored protein, on peripheral neutrophils in patients compared with those in age- and sex-matched healthy controls, whereas the levels of CD11a and CD11b expression were similar. The chemotactic response of neutrophils was lower toward not only formyl-methionyl-leucyl-phenylalanine but also complement fragment C5a than that of healthy controls. The expression of another GPI-anchored protein, CD14, was equally expressed by controls and patients. Therefore, the low level of CD16 expression was not due to the incomplete synthesis of the GPI anchor. GPI anchors of CD16 on neutrophils from controls and patients were both partially resistant to phosphatidylinositol-specific phospholipase C. The presence of promyelocytes in peripheral blood, low expression of CD16, and low chemotactic response of neutrophils suggest that patients with EOP have an abnormal maturation system in myeloid lineage cells in the bone marrow, which may be associated with the onset and course of EOP.

The LW blood group glycoprotein is homologous to intercellular adhesion molecules

The LW blood group antigens reside on a 42-kDa erythrocyte membrane glycoprotein that was purified by immunoaffinity and partially sequenced. From this information, a specific PCR-amplified DNA fragment was used to screen a lambda gt11 human bone marrow cDNA library. Two forms of cDNA were isolated; the first encoded a single spanning transmembrane protein of 270 amino acids, including a 29-amino acid peptide signal and four potential N-glycosylation sites, and the second encoded a shortened protein form of 236 residues devoid of transmembrane and cytoplasm domains. A rabbit antibody raised against the 15 N-terminal amino acids of the predicted protein reacted on immunoblots with authentic LW glycoprotein and in indirect agglutination test with all human erythrocytes except those from LW(a-b-). This showed that the protein encoded by these clones was LW gene product and suggested that the N terminus of the LW protein is oriented extracellularly. Most interestingly, the LW protein was found to exhibit sequence similarities (with approximately 30% identity) with intercellular adhesion molecules ICAM-1, -2, and -3, which are the counter-receptors for the lymphocyte function-associated antigens LFA-1. The extracellular domain of LW consists, like that of ICAM-2, of two immunoglobulin-like domains, and the critical residues involved in the binding of LFA-1 to ICAMs were partially conserved in LW.

Lymphocyte emperipolesis in human glial cells

Astrocytes have been observed to contain intact, viable lymphocytes within their cytoplasm (emperipolesis) in multiple sclerosis plaques and some brain tumors. This study characterizes the adhesive, emperipoletic and phagocytic properties of glial cells in culture. Human fetal and adult astrocytes engaged in adhesion and emperipolesis of lymphocytes. Emperipolesis, and not adhesion, was temperature- and cation-dependent. The CD8 and MHC Class I antigens played a role in emperipolesis. Lymphocytes most often remained viable within the cytoplasm of astrocytes but occasionally underwent lysis or caused disruption of the astrocyte intermediate filaments. The phenomenon of emperipolesis is distinct from phagocytosis, since microglia showed prominent phagocytic properties but did not engage in emperipolesis. Conversely, astrocytes were efficient emperipolites and rarely demonstrated phagocytic properties.

Adhesion molecules on CD34+ hematopoietic cells in normal human bone marrow and leukemia

Expression of selected adhesion molecules of the integrin and immunoglobulin family was investigated on CD34+ leukemic cells in 19 AML and 11 ALL cases to evaluate phenotypic differences in adhesive properties of malignant hematopoietic precursor cells in comparison to normal bone marrow CD34+ cells. Of the beta 2-integrin family, CD11a was expressed on > 50% of CD34+ cells in normal bone marrow and almost all leukemias, whereas CD11b and CD11c were not expressed on CD34+ cells in normal bone marrow, but were found on CD34+ blasts in some leukemias of a heterogeneous immunophenotype. Of the beta 1-family, CDw49d (VLA-4) was strongly expressed on normal CD34+ bone marrow cells and on the blasts of all 30 CD34+ leukemic samples, whereas CDw49b (VLA-2) was absent on CD34+ cells in normal bone marrow, but detected on CD34+ cells in a few leukemias which did not constitute a clinical or phenotypic entity according to the FAB classification or immunocytological analysis. The lymphocyte-homing-associated adhesion molecule CD44 (HCAM) and CD58 (LFA-3) were expressed on CD34+ cells in all investigated cases of normal and leukemic bone marrow. ICAM-1 (CD54), the inducible receptor ligand for CD11a/CD18, although present on CD34+ cells in normal bone marrow, was lacking on blast cells of some ALL and AML cases. So far, the variable expression of beta 2-integrins as well as of VLA-2 and of ICAM-1 could indicate distinct differences in cell-cell or cell-matrix adhesion of leukemic cells in ALL and AML patients.

Expression of leukocyte adhesion molecules by mucosal mononuclear phagocytes in inflammatory bowel disease

Leukocyte adhesion molecules are important in cell-cell interactions of the immune system. Lymphocyte function-associated antigen 1 (cluster designation 11a) mediates interactions between T cells and mononuclear phagocytes through its ligand, the intercellular adhesion molecule 1 (CD54), whereas complement receptors 3 (CD 11b) and 4 (CD11c) are involved in complement-mediated phagocytosis. Expression of CD11 molecules and intercellular adhesion molecule 1 was studied in colonic biopsy specimens from 20 patients with inflammatory bowel disease and 10 normal controls. In normal colon, few mononuclear phagocytes expressed lymphocyte function-associated antigen 1 and intercellular adhesion molecule 1 at high densities. The major adhesion molecule was CD11c. Thus, the largest population of normal colonic mononuclear phagocytes was represented by quiescent, resident macrophages with likely phagocytic function. In inflammatory bowel disease, mononuclear phagocytes showed only a slight increase in CD11a expression and no significant change in expression of CD11b and CD11c. By contrast, the percentage of mononuclear phagocytes expressing intercellular adhesion molecule 1 was increased from 6.9% +/- 3.9% in controls to 69.2% +/- 12.8% in ulcerative colitis (P less than 0.001) and to 45.7% +/- 22.8% in Crohn's disease (P less than 0.01), showing a close relationship with histological activity. The increased expression of intercellular adhesion molecule 1 in inflammatory bowel disease indicates a state of immunological activation induced by local release of inflammatory cytokines. Such induction of intercellular adhesion molecule 1 on mononuclear phagocytes may be important in the maintenance of chronic inflammation by facilitating interactions with T cells and T-cell antigen recognition.

Expression and modulation by cytokines of the intercellular adhesion molecule-1 (ICAM-1) in human central nervous system tumor cell cultures

The intercellular adhesion molecule (ICAM-1) has been shown to be important in interactions involving cells of the immune system and to be upregulated in a number of cell culture systems by cytokines, including immune interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In the present study, we have determined by fluorescence-activated cell sorter (FACS) analysis and the anti-ICAM-1 monoclonal antibody (MAb) CL203.4 the base-line expression of ICAM-1 and its modulation by recombinant IFN-beta, IFN-gamma and TNF-alpha in early passage (less than 15) human central nervous system (CNS) tumor-derived cell cultures. These cultures were established from various malignancies, including glioblastoma multiforme (GBM), astrocytoma (AST), ganglioglioma, medulloblastoma, meningioma and a pineal tumor. ICAM-1 expression was highest in the GBM- and AST-derived cell cultures and was lowest in the ganglioglioma and normal pineal cell cultures. Variable ICAM-1 expression was found, however, in tumors of the same histological group. In several cell cultures the variable expression observed by FACS was substantiated by the intensity of the molecular species immunoprecipitated by the anti-ICAM-1 MAb CL203.4 from these cells. All the cell cultures displayed variable but consistent increases in ICAM-1 expression following treatment with IFN-gamma or TNF-alpha. In general, the degree of increase in ICAM-1 expression was greatest in cultures exposed to TNF-alpha. Upregulation of ICAM-1 expression in an established glioblastoma multiforme cell line was of greater magnitude and more rapid following TNF-alpha treatment (within 2 to 3 hr) than exposure to IFN-gamma (by 24 hr). In several cultures, IFN-beta also increased ICAM-1 expression and enhanced the increase induced by TNF-alpha. The results of the present study indicate that variable expression of ICAM-1 is a common property of early passage cultures of CNS tumors and recombinant interferons and TNF-alpha can differentially upregulate ICAM-1 expression in these CNS tumor cell cultures.

Phenotypic analysis of a large number of normal human bone marrow sample by flow cytometry

Bone marrow aspirates from 48 healthy donors (34 adults, 14 children) were analyzed by flow cytometry (FACS Analyzer) after purification of low-density bone marrow cells (Ld BMC) on a density gradient (d = 1,077) and labelling with 23 anti-hematopoietic cell monoclonal antibodies. Based on physical properties, these Ld BMC could be divided into four different populations called E, My, Mo and L, which comprised 14% +/- 9%, 31% +/- 16%, 10% +/- 5% and 45% +/- 14% of these cells, respectively. The phenotypic analysis of these different populations enabled the identification in E, of erythrocytes (Glycophorin A+, Rhesus D+, but negative for early erythroid differentiation markers such as the transferrin receptor (Tf. R) and the FA6-152 antigen); in My of cells of the myeloid lineage (VIM2+, HLA DR-); in Mo of cells of the monocytic lineage (VIM2+, CD14+) plus some myeloblasts (VIM2+, CD14-, HLADR+) and finally in L of a heterogeneous population including: 1. T lymphocytes labelled to the same extent by CD2, CD3, CD5 and CD6 (28% +/- 10%), B lymphocytes assessed by CD19 and CD20 (12% +/- 8%), Pre-B cells (CD10+ = 8% +/- 7%), less than 5% of "natural killer" cells (CD16+ or Leu7+) and finally, less than 6% of myelomonocytes (CD14+ and/or VIM2+). 2. The erythroid lineage (rhesus D+ = 42% +/- 20%, Tf.R+ and FA6-152+ = 32% +/- 12%). 3. Undifferentiated cells or progenitor cells (CD34+ = 7% +/- 5%). 4. Cells unlabelled by any antibodies (approximately 6%). We observed no difference between bone marrow samples from adults or children, with respect to physical properties, and with all but four immunological markers. A significantly higher proportion of B cells (CD19+ and CD10+) (P less than 0.001) and undifferentiated cells (CD34+ and HLADR+) (P less than 0.02) was observed in children. These data, obtained from a large number of bone marrow samples, could be used to quantify the imbalance of some bone marrow disorders.

Expression of integrins in human bone marrow

Expression of integrins, a superfamily of glycoprotein alpha/beta heterodimers which integrate the cytoskeleton with the extracellular matrix and/or mediate cell-cell adhesive interactions, was examined on normal and leukaemic bone marrow cells by immunohistochemistry and immunotransmission electron microscopy (immuno-TEM). Among the beta 1/VLA molecules studied, VLA-2 and 6 were expressed on megakaryocytes and platelets, while VLA-4 was present on 40% of haemopoietic cells, including monocytes, erythroblasts and immature cells; this molecule was typically localized at sites of intercellular contact, as seen by immuno-TEM, suggesting it may be involved in interactions among haemopoietic cells during differentiation. In human long-term bone marrow cultures (LTBMC), VLA-1 and 3 were present respectively on 35% and 40% of the adherent cells which included fibroblasts and endothelial cells, as shown by double-labelling experiments; VLA-2 was expressed only on a subpopulation of fibroblasts. beta 2/LeuCAM molecules were absent from platelets, megakaryocytes and HLA-DR+/myeloperoxidase- early myeloid precursors, and appeared progressively during maturation in both lymphoid and myeloid cells. Expression of beta 3/cytoadhesin molecules was restricted to megakaryocytes and platelets and, in the adherent layer of LTBMC, to endothelial cells. The regulated expression and specific localization of integrins in the bone marrow suggest that these molecules may have a role in normal haemopoiesis.

Production and characterization of monoclonal anti-CD18 anti-idiotype antibodies

Three leukocyte adhesion receptors have been described which mediate intercellular binding of leukocytes: LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and p150/95 (CD11c/CD18). We have previously reported the production of several monoclonal antibodies against the common subunit of these receptors (CD18). We have describe the production of monoclonal anti-idiotype antibodies against one of the anti-CD18 antibodies (H52) which has been shown to inhibit potently the function of leukocyte adhesion receptors. Three IgG1 and two IgM anti-idiotype antibodies were derived which recognized private idiotopes on the H52 molecule. Two of these antibodies blocked the binding of H52 to purified LFA-1 and to cell surface expressed antigen. One of the antibodies (AIM.6) was shown to be an internal image-type (Ab2 beta) antibody based on inhibition of its binding to H52 by purified LFA-1 and by its ability to induce Ab3 which recognize LFA-1 when used as immunogen. The AIM.6 Ab2 beta antibody was tested for recognition of leukocyte adhesion ligands in LFA-1-mediated leukocyte adhesion and activation assays. The AIM.6 antibody did not block intercellular adhesion of leukocytes or mitogen stimulation of T cells, functions which were completely inhibited by low concns of H52. AIM.6 Ab2 beta antibody bound to H52 very well at 0 degrees C but bound very poorly or not at all at 37 degrees C. Binding studies on a panel of anti-CD18 monoclonal antibodies showed that the idiotope defined by AIM.6 was unique to H52 and an antibody recognizing the same epitope on CD18 (H5B9). This result showed that inhibitory anti-CD18 monoclonal antibodies utilize at least two distinct paratopes in binding to CD18. The above results are in contrast to those obtained in other systems in which Ab2 beta antibodies against receptor-specific Ab1 antibodies recognize receptor ligands and are discussed in the context of ligand recognition by leukocyte adhesion receptors.

The induction of intercellular adhesion molecule 1 (ICAM-1) expression on human fetal astrocytes by interferon-gamma, tumor necrosis factor alpha, lymphotoxin, and interleukin-1: relevance to intracerebral antigen presentation

Antigen presentation reactions are dependent upon the expression of the class II major histocompatibility antigens (MHC), the T-cell receptor, and the presented antigen. Recent studies demonstrate that such processes also require the presence of adhesion molecules such as lymphocyte functional antigen 1 (LFA-1) and its cell surface ligand, intercellular adhesion molecule 1 (ICAM-1). It has been suggested that the brain astrocyte can function as a facultative antigen presenting cell (APC). This hypothesis is based upon the ability to induce the expression of the class II MHC antigens on astrocytes, and on their ability to present myelin basic protein to encephalitogenic T-cells in vitro. The best in vivo data showing that astrocytes serve as intracerebral APCs is the finding that astrocytes in multiple sclerosis plaques are DR+ (class II MHC in human). However, it still remains to be resolved whether the in vivo expression of the MHC antigens in disease states is instrumental to antigen presentation mechanisms or whether these cell surface glycoproteins are expressed secondary to brain immune responses. If astrocytes function as immunocompetent APCs within the brain, it would seem that they would also be able to express molecules important for intercellular adhesion. Here, we present the first data that indicates that human astrocytes are capable of expressing ICAM-1 in response to cytokines that either induce or upregulate the expression of DR. In essence, cytokines derived from different cell types seem to exert similar pleiotropic effects on the modulation of MHC and ICAM-1 expression on astrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenotype and function of peripheral blood and bone marrow T-cell colonies: identification of DC3-, 4-, 8-autoreactive T cells

The existence of immature autoreactive T cells has been examined in peripheral blood (PB) and bone marrow (BM) derived T-lymphocyte colonies (TLC) that have previously been shown to be potentially generated from CD3-negative BM-T cells. An extensive phenotypical analysis of total and T-depleted TLC showed that both PB- and BM-derived TLC contained a mean of 5% immature T lymphocytes (ITL), which were negative for the CD3, CD4, and CD8 antigens but displayed the CD2 and CD7 antigens. The only detectable immune functions of these isolated ITL were an allo- and an autoreactivity without cytolytic activity. The self-reactivity of ITL was not detected in bulk non T-depleted TLC cells and seemed to be actively suppressed by autologous mature T cells. In addition, the auto-MLR of ITL was totally inhibited by anti-HLA class II but not by anti-class I monoclonal antibody (MoAb) and only partially by anti-CD4 moAb, whereas the anti-CD3 and anti-CD2 MoAbs gave no inhibition. Once activated, ITL could acquire in culture a mature T cell CD3 + CD4 + phenotype. The CD3-, 4-, 8-auto-reactive T cells present in T colonies could represent pre- or post-thymic cells that have not yet undergo or that have escaped the thymic selection.

Cell to cell contact enhances the proliferation of acute myeloid leukemia (AML) cells in vitro without an apparent role of adhesion glycoproteins LFA1, MAC1 and P150-95

Acute myeloblastic leukemia (AML) cells were cultured under conditions facilitating or preventing cell to cell contact. Proliferation of AML blasts of 24 patients was assessed in semisolid (containing 0.9% methylcellulose) and in liquid cultures, in which identical concentrations of colony stimulating factors (CSFs) had been provided. In all but one of the cases, significant DNA synthesis (evaluated by 3H-thymidine uptake) was observed when the cells were incubated in the liquid system, whereas in only 14 cases (58%), the cells were able to form clusters or colonies in the semisolid system. These findings suggest that AML cells from a large proportion of patients can proliferate only after stimulation with CSFs in a liquid system, i.e. when cultured under conditions permitting reciprocal contact between the cells. To establish further the importance of cell to cell contact for AML cell proliferation, cells from 19 patients were cultured in liquid medium concurrently in flat bottom microwells (in which a majority of the cells lie separate) and in round bottom microwells (in which cells show a tendency to aggregate). A significantly higher 3H-thymidine (TdR) incorporation in the round bottom cultures was observed in 15 out of 19 cases. The role of the leukocyte function antigens (LFA) LFA1, Mac1, P150-95 in this phenomenon was then analyzed, as these structurally related glycoproteins are involved in reactions requiring contact between hematopoietic cells. Membrane expression of the three antigens was first examined in 16 patients. LFA1, Mac1 and P150-95 were expressed on the AML cells of 15, 6 and 8 patients, respectively. Expression of these antigens did not change following short term incubation of the AML cells in the presence of CSFs. AML cells cultured in presence of saturating concentrations of monoclonal antibodies reacting with structures of these 3 antigens in order to abrogate their function did not suppress 3H-TdR uptake. Thus, no direct role for LFA1 and/or Mac1 and/or P150-95 antigens in mediating contact-induced AML proliferation could be demonstrated. It remains to be established which components are involved in the cell-cell contact-mediated upregulation of AML cell proliferation.

Astrocytes and intracerebral immune responses

The astrocyte is the most abundant cell within the central nervous system (CNS). This cell subserves a multiplicity of important functions that contribute to the process of neural development as well as to the integrity of normal brain function. Adding to the already exhaustive list of capabilities, the astrocyte has now been demonstrated to function as an intracerebral antigen presenting cell. These findings are serving to revise our view of the brain as an immunoprivileged site and perhaps will shed some light on the pathogenetic mechanisms involved in a number of CNS disorders of immune dysregulation. In this review we provide some perspective on the regulatory mechanisms that influence astrocyte immune functions. Specifically, we address the role played by the major histocompatibility complex (MHC) antigens as well as adhesion molecules in the initiation of brain immune responses.

Early events in human T cell ontogeny. Phenotypic characterization and immunohistologic localization of T cell precursors in early human fetal tissues

During early fetal development, T cell precursors home from fetal yolk sac and liver to the epithelial thymic rudiment. From cells that initially colonize the thymus arise mature T cells that populate T cell zones of the peripheral lymphoid system. Whereas colonization of the thymus occurs late in the final third of gestation in the mouse, in birds and humans the thymus is colonized by hematopoietic stem cell precursors during the first third of gestation. Using a large series of early human fetal tissues and a panel of monoclonal antibodies that includes markers of early T cells (CD7, CD45), we have studied the immunohistologic location and differentiation capacity of CD45+, CD7+ cells in human fetal tissues. We found that before T cell precursor colonization of the thymus (7-8 wk of gestation), CD7+ cells were present in yolk sac, neck, upper thorax, and fetal liver, and were concentrated in mesenchyme throughout the upper thorax and neck areas. By 9.5 wk of gestation, CD7+ cells were no longer present in upper thorax mesenchyme but rather were localized in the lymphoid thymus and scattered throughout fetal liver. CD7+, CD2-, CD3-, CD8-, CD4-, WT31- cells in thorax and fetal liver, when stimulated for 10-15 d with T cell-conditioned media and rIL-2, expressed CD2, CD3, CD4, CD8, and WT31 markers of the T cell lineage. Moreover, CD7+ cells isolated from fetal liver contained all cells in this tissue capable of forming CFU-T colonies in vitro. These data demonstrate that T cell precursors in early human fetal tissues can be identified using a mAb against the CD7 antigen. Moreover, the localization of CD7+ T cell precursors to fetal upper thorax and neck areas at 7-8.5 wk of fetal gestation provides strong evidence for a developmentally regulated period in man in which T cell precursors migrate to the epithelial thymic rudiment.

Absence, or low expression, of leukocyte adhesion molecules CD11 and CD18 on Burkitt lymphoma cells

Leukocyte adhesion to cells is mediated by the cell-surface glycoprotein complex CD11a-c/CD18 and, in some cases, the glycoprotein gp84. The process is associated with leukocyte activation and modulates lymphocyte proliferation and maturation. Epstein-Barr virus (EBV)-transformed normal B lymphocytes give rise to lymphoblastoid cell lines (LCLs) which grow as large clusters mediated by adhesion molecules. In contrast, newly explanted EBV-infected Burkitt lymphoma (BL) cells usually grow as single cells or as loose clusters. We now report that EBV positive- and EBV-negative BL lines lack the adhesive protein complex, or have only low levels of it, whereas LCLs, representing various stages of B-lymphocyte development, contain considerably higher amounts, as measured by immunofluorescence flow cytometry and immunoprecipitation. The level of gp84 expression is of the same magnitude in both types of cells.

The function of human intercellular adhesion molecule-1 (ICAM-1) in the generation of an immune response

Monoclonal antibody RR 1/1 directed against the putative LFA-1 ligand molecule intracellular adhesion molecule-1 (ICAM-1) was found to inhibit the T cell proliferative response to the antigen PPD. Interestingly, the percentage of unstimulated monocytes which expressed ICAM-1 on their surface appeared to vary greatly from person to person although the majority of monocytes did express high levels of ICAM-1 within their cytoplasm and surface expression could be rapidly induced on most cells by adherence to fibronectin. Resting T cells showed no evidence of surface or cytoplasmic ICAM-1 although expression was induced both within the cell and on the membrane as a result of activation with phytohemagglutinin or a combination of OKT3 and phorbol 12,13-dibutyrate. The significance of these findings with respect to the function of monocyte and T cell in the generation of an immune response is discussed.

The role of monocyte lymphocyte function-associated antigen 1 (LFA-1) in accessory cell function

Monoclonal antibodies directed against the common beta subunit shared by lymphocyte function-associated antigen-1 (LFA-1), CR3 and p150,95 or the alpha subunit of LFA-1, inhibited the T lymphocyte proliferative response to tetanus toxoid, pokeweed mitogen-1 and OKT3 but had little or no effect on the response to the leukoagglutinating lectins pokeweed mitogen-2 and phytohemagglutinin. The LFA-1 molecule was shown to participate in the adhesive interaction between monocytes and T lymphocytes that was required for the initiation of an immune response. Both monocyte and T lymphocyte LFA-1 were found to contribute to this interaction. These results further define the part played by the LFA-1 molecule in the activation of T lymphocytes.

Prevention of graft failure by an anti-HLFA-1 monoclonal antibody in HLA-mismatched bone-marrow transplantation

Seven patients with immunodeficiencies (Wiskott-Aldrich syndrome, combined immunodeficiency, and osteopetrosis) were given a mouse monoclonal antibody against the alpha subunit of human leucocyte functional antigen (HLFA-1; CD18) to facilitate the engraftment of mismatched haploidentical related-donor bone marrow. Other conditioning included busulphan, cyclophosphamide, and antilymphocyte globulin. To prevent graft-versus-host disease the bone-marrow T cells were depleted with sheep erythrocyte rosetting and cyclosporin therapy was given. HLFA-1 antibody injections were well tolerated without side-effects except slight, transient fever (38-40 degrees) after the first injection. Engraftment was rapid in all seven patients. The regenerating leucocytes were of donor origin in all cases, and two patients have a mixed chimera. Two patients died from infections. The others are alive and well 60-395 days after transplantation. In a historical control group given the same treatment without anti-HLFA-1 infusion, only one of seven transplants partially engrafted; only two patients remain alive with autologous reconstitution but with uncorrected immunodeficiency.