Bovine microvascular endothelial cells (BMECs) proliferated to confluence on the stromal surface of human amniotic membrane that had been denuded of its natural epithelium . The resulting cultures had the following characteristics : (a) The endothelial cells formed a thin, continuous monolayer and, like their in vivo counterparts, contained basal adhesion plaques and large numbers of cytoplasmic vesicles and 10-nm filaments . In addition, the endothelial cells elaborated a basement membrane-like structure . The microvascular endothelium plays an important role in regulating the exchange of fluid, macromolecules, and cells between the blood and the extravascular tissue . Studies of the mechanisms that underlie these exchanges have been limited by the lack of a simple and relevant in vitro model of the microvessel wall. The basic requirements for such a model are a suitable strain of endothelial cells and a substrate on which a monolayer of the cells can be maintained in a welldifferentiated state . For these monolayers to be useful in examining the transendothelial movement of materials and cells, it is important that they possess permeability characteristics that are similar to those of endothelium in vivo. That is, the endothelial cells must form intercellular junctions that exclude appropriate macromolecular probes and resist the passage of electrical current.We have developed an in vitro model of a microvessel wall that consists of cloned bovine microvascular endothelial cells (BMECs)' cultured on connective tissue prepared from hu-'Abbreviations used in this paper: BMECs, bovine microvascular endothelial cells ; HIDCS, heat-inactivated donor calf serum ; aMEM, minimal essential medium, alpha modification ; WGA-HRP, wheat germ agglutinin coupled to horseradish peroxidase .

Programmed cell death, also known as apoptosis, is frequently initiated when cells are deprived of specific trophic factors. To investigate if accelerated apoptosis contributes to the pathogenesis of Diamond- Blackfan anemia (DBA), a rare pure red blood cell aplasia of childhood, we studied the effect of erythropoietin (epo) deprivation on erythroid progenitors and precursors from the bone marrow of DBA patients as compared with hematologically normal controls. Apoptosis in response to epo deprivation was evaluated by enumeration of colony-forming unit- erythroid (CFU-E)- and burst-forming unit-erythroid (BFU-E)-derived colonies in plasma clot semisolid culture and by the identification of typical DNA oligosomes by gel electrophoresis from marrow mononuclear cells in liquid culture. In all DBA patients there was a marked decrease in CFU-E- and BFU-E-derived colony formation compared with normal controls at comparable time points of epo deprivation, with a complete loss of CFU-E-derived colonies in semisolid culture by 9 hours of epo deprivation versus 48 hours in controls. The BFU-E-derived colony response to epo deprivation displayed a similar pattern of decrement. Apoptotic changes assessed by the presence of characteristic DNA fragmentation began in the absence of epo deprivation and were readily detected within 3 hours of epo deprivation in DBA cultures versus 9 hours in controls. We conclude that DBA is characterized by accelerated apoptosis as measured by the loss of erythroid progenitor clonogenicity and increased progenitor and precursor DNA fragmentation leading to the formation of characteristic oligosomes, consistent with an intrinsic erythroid-progenitor defect in which increased sensitivity to epo deprivation results in erythroid failure.

The distribution of intercellular adhesion molecule-1 (ICAM-1), a ligand for lymphocyte function antigen-1, on hematopoietic tissue was determined using the anti-ICAM-1 monoclonal antibody CL203.4 with flow cytometry and short-term semi-solid hematopoietic progenitor cultures. After timed incubation in media with fetal bovine serum, 29% of erythroid burst-forming units (BFU-E), 24% of erythroid colony-forming units (CFU-E), and 52% of granulocyte-macrophage colony-forming units (CFU-GM) bone marrow progenitors expressed ICAM-1. This finding, which is consistent with the detection of ICAM-1 on acute non-lymphoblastic leukemic blasts, is at variance with recent reports. ICAM-1 was also detected on bone marrow blasts, proerythroblasts, promyelocytes, and cells of monocyte/macrophage lineage, but was not detected on erythroblasts, normoblasts, neutrophilic myelocytes, metamyelocytes, bands, or on most lymphocytes. These results indicate that maturation of cells of the erythroid and myeloid lineage is associated with loss of ICAM-1. The distribution of ICAM-1 on bone marrow progenitors, early precursor cells, and accessory cells in conjunction with the function of this molecule in cell-cell interactions suggests that ICAM-1 may play a role in the cell-cell and cell-stromal interactions that regulate hematopoiesis.

The distribution of intercellular adhesion molecule-1 (ICAM-1), a ligand for lymphocyte function antigen-1, on hematopoietic tissue was determined using the anti-ICAM-1 monoclonal antibody CL203.4 with flow cytometry and short-term semi-solid hematopoietic progenitor cultures. After timed incubation in media with fetal bovine serum, 29% of erythroid burst-forming units (BFU-E), 24% of erythroid colony-forming units (CFU-E), and 52% of granulocyte-macrophage colony-forming units (CFU-GM) bone marrow progenitors expressed ICAM-1. This finding, which is consistent with the detection of ICAM-1 on acute non-lymphoblastic leukemic blasts, is at variance with recent reports. ICAM-1 was also detected on bone marrow blasts, proerythroblasts, promyelocytes, and cells of monocyte/macrophage lineage, but was not detected on erythroblasts, normoblasts, neutrophilic myelocytes, metamyelocytes, bands, or on most lymphocytes. These results indicate that maturation of cells of the erythroid and myeloid lineage is associated with loss of ICAM-1. The distribution of ICAM-1 on bone marrow progenitors, early precursor cells, and accessory cells in conjunction with the function of this molecule in cell-cell interactions suggests that ICAM-1 may play a role in the cell-cell and cell-stromal interactions that regulate hematopoiesis.

Monolayers of bovine microvascular endothelial cells (BMECs) grown on connective tissue derived from human amniotic membrane were used to examine the transendothelial migration of human neutrophils in vitro. Neutrophils placed above these cultures migrated in response to a chemotactic gradient generated by placing 10(−7) M-formyl-methionyl-leucyl-phenyl-alanine (fMLP) below the cultures. Under these conditions, an average of 29 +/− 12% of the total population of neutrophils migrated beneath the endothelium after 1 or 2 h of incubation. Neutrophil migration in the absence of fMLP or in the presence of equal concentrations of fMLP above and below the cultures was less than 8% of the response to a 10(−7) M-fMLP gradient. Migration was a rapid event. Neutrophils began adhering to the apical surface of the endothelium within 2 min following exposure to an fMLP gradient; Ca2+ was required for this initial adhesion. Within 10 min, the majority of neutrophils associated with the BMEC-amnion cultures had migrated beneath the endothelial monolayer. Ultrastructural studies revealed that the initial adhesion between migrating neutrophils and endothelium was characterized by close contact between the two types of cell in focal areas. This close association was maintained as the neutrophils traversed the clefts between endothelial cells. Following their migration across the endothelium, neutrophils often were observed lying between the endothelium and its basement membrane. With time, the neutrophils penetrated the basement membrane and moved into the underlying amniotic connective tissue. To test the role of neutrophil proteinases in breaching endothelial and subendothelial barriers, migration was allowed to proceed in the presence of a variety of proteinase inhibitors, including p-nitrophenyl p'-guanidinobenzoate, soybean trypsin inhibitor, 6-aminocaproic acid, alpha 1-proteinase inhibitor, leupeptin, antipain and methoxysuccinyl alanine-alanine-proline-valine chloromethyl ketone. None of these had a significant effect on the number of neutrophils that migrated or the depth to which they penetrated the amniotic tissue as compared with controls. In contrast, pepstatin and chymostatin reduced migration in response to fMLP to 7% and 52% of control values, respectively. However, these two inhibitors did not affect migration in response to another chemoattractant, leukotriene B4. Migration was neither enhanced nor inhibited by the following treatments: (1) removal of plasminogen from the calf serum used in the assay medium and addition of polyclonal antibody to plasminogen; (2) addition of monoclonal or polyclonal antibody to plasminogen activator.(ABSTRACT TRUNCATED AT 400 WORDS)