Eleven novel mutations in the factor VIII gene from Brazilian hemophilia A patients

The molecular characterization of the mutations in hemophilia A patients is hampered by the large size of the factor VIII gene and the great heterogeneity of mutations. In this study, we have performed a protocol involving multiplex polymerase chain reaction in which 19 exons were amplified in four different combinations followed by nonradioactive single-strand conformational polymorphism (SSCP) to screen for mutations. Southern blotting was used to detect inversion of the factor VIII gene resulting from recombination between copies of the gene A (F8A) located in intron 22 of the factor VIII gene and two copies close telomeric region of X chromosome. Forty-two hemophilia A patients (21 with severe and 21 with mild-to-moderate disease) were studied. The inversion of factor VIII occurred in 13 of 21 patients affected by severe hemophilia A. One patient showed a large extra band in addition to the three bands observed after Southern blotting with the F8A probe. An abnormal electrophoretic pattern of SSCP was detected in 85% and 50% of the patients affected by mild-to-moderate and severe disease, respectively. Sixteen different mutations were identified. Eleven mutations were novel and comprised 9 point mutations and 2 small deletions. This study shows that the methodology used is safe and rapid and has potential for detecting almost all of the genetic defects of the studied hemophilia A patients.     

Beta 2-microglobulin is not required for cell surface expression of the murine class I histocompatibility antigen H-2Db or of a truncated H-2Db.

beta 2-Microglobulin (beta 2m) has been thought essential for transport of all major histocompatibility complex class I antigens to the cell surface. Here, we show that the mouse class I antigen H-2Db is expressed at the cell surface even when there is no beta 2m present within the cell. This was established by transfecting the H-2Db gene into the R1E cell line, which lacks beta 2m. The conformation of the Db antigen expressed by the R1E transfectant is very different from that of the native molecule. This Db antigen is not recognized by Db-allospecific and Db-restricted cytotoxic T lymphocytes or by most monoclonal antibodies to the native Db. We show further that a deletion construct of the Db gene, which consists of exon 1 linked to exons 4-8, expresses a truncated Db antigen lacking domains 1 and 2 [Db-(1 + 2)] at the cell surface after transfection into the R1E line. Previous biochemical and crystallographic data have indicated that domain 3 is associated with beta 2m; unexpectedly, Db-(1 + 2) does not associate with beta 2m when the mouse beta 2mb gene is transfected into the R1E transfectant expressing the truncated Db. This suggests that interactions with domains 1 and 2 are important for the paired association of domain 3 and beta 2m in the native Db antigen.     

"Stem cell" origin of the hematopoietic defect in dyskeratosis congenita

We have used the long-term bone marrow culture (LTBMC) system to analyze hematopoiesis in three patients with dyskeratosis congenita (DC), two of whom had aplastic anemia, and the third had a normal blood count (apart from mild macrocytosis) and normal BM cellularity. Hematopoiesis was severely defective in all three patients, as measured by a low incidence of colony-forming cells and a low level of hematopoiesis in LTBMC. The function of the marrow stroma was normal in its ability to support the growth of hematopoietic progenitors from normal marrows seeded onto them in all three cases, but the generation of hematopoietic progenitors from patients marrow cells inoculated onto normal stromas was reduced, thus suggesting the defect to be of stem cell origin. The parents and unaffected brother of one of the families have also been studied in LTBMC and all showed normal hematopoietic and stromal cell function. From this study we speculate that there are some similarities between DC and the defect in the W/Wv mouse.     

Down-modulation of neutrophil production by erythropoietin in human hematopoietic clones

In clonogenic assays of hematopoietic progenitors, high concentrations (4 U/mL) of erythropoietin (epo) reduced the formation of granulocyte- macrophage (GM) colonies and diminished the number of granulocytes formed per culture plate. Fetal progenitors were more sensitive to these effects of epo than were progenitors from adults, displaying these reductions at greater than or equal to 1 U epo/mL. The mechanism was investigated by growing fetal progenitors stimulated by recombinant GM-CSF, in the absence of epo, and when eight-cell clones first appeared, mapping their location, then adding epo, and assessing its effect on the subsequent differentiation of the clones. In the absence of epo, the clones developed exclusively into GM colonies. However, if developing clones were presented with epo, 85% matured into GM colonies, but 15% became multilineage or normoblast colonies. In addition, developing clones that were presented with epo produced colonies that contained fewer neutrophils. These effects of epo on neutrophil generation were observed with each of three varieties of recombinant epo, and also with purified human epo, but were not observed using epo that had been neutralized with rabbit anti-epo antiserum.     

Processing of lysozyme by macrophages: identification of the determinant recognized by two T-cell hybridomas.

The purpose of this study was to identify the fragment of the hen egg-white lysozyme (HEL) molecule presented by macrophages to helper T cells. This was investigated by using T-cell hybridomas and macrophages prefixed in paraformaldehyde. We previously had shown that such prefixed macrophages could present a tryptic digest of HEL. The tryptic peptides were separated by HPLC and tested for their ability to stimulate the T-cell hybridomas. Only one tryptic peptide was found to be immunogenic. This immunogenic peptide was identified as the tryptic peptide T-8, containing amino acids 46-61. The precise determinant on the peptide T-8 being recognized was further defined by testing the response of the two T-cell hybridomas to human lysozyme. Neither clone responded to human lysozyme. From the amino acid sequence of human lysozyme, the determinant was localized to the four amino-terminal residues. Cleavage of the immunogenic peptide with either chymotrypsin or protease V-8 completely abolished the immunogenicity. This suggested that the T-cell determinant is located in the hydrophilic amino-terminal residues and that it must be associated with a hydrophobic stretch of amino acids, which allows the peptide to associate with the macrophage plasma membrane.     

Natural history of early diabetic nephropathy: What are the effects of therapeutic intervention?

Several studies have shown that lowering of blood pressure slows the rate of progression of diabetic renal disease. Some placebo-controlled studies have also shown that angiotensin-converting enzyme (ACE) inhibitors decrease or stabilize albuminuria in incipient nephropathy and slow the rate of progression of advanced nephropathy. However, it is not yet clear if prolonged treatment with ACE inhibitors or with other agents exerts a specific renoprotective effect in incipient diabetic nephropathy. It is proposed that such an effect should be independent from changes in systemic blood pressure and should be characterized by amelioration of the rate of rise of albumin excretion rate (AER) and the rate of fall of glomerular filtration rate (GFR) and independence from changes in other parameters known to influence AER (glycemic control, protein intake, sodium intake). In addition, there should be evidence that the potentially reversible effects of therapeutic intervention on AER and GFR are translated to long-term changes in renal function and structure. This paper reviews the evidence on which the concept of renoprotection is based, with particular reference to choice of end points, heterogeneity of study groups, and complexities of the disease process, and relates this evidence to the natural history of nephropathy in type I and type II diabetes. Based on the above, an assessment is made of the comparative effects of ACE inhibitors and other antihypertensive agents on AER and GFR. It is suggested that longitudinal intra-individual analysis of both variables may be necessary in order to determine whether ACE inhibitors exert greater renoprotection than calcium channel blockers or other antihypertensive agents.     

Abnormalities in pathways of alveolar fibrin turnover among patients with interstitial lung disease

Fibrin deposition is prominent in the histopathologic features of chronic interstitial lung disease. Human alveolar macrophages can potentially modulate this process because normal macrophages synthesize and express the initial enzymes of both coagulation and fibrinolytic pathways. In the present study, we examined the cell-associated procoagulant activity of macrophages lavaged from patients with sarcoidosis (n = 14) or idiopathic pulmonary fibrosis (n = 13) and compared the enzyme activities with that of a group of normal volunteers (n = 16). Cells from sarcoid patients had a mean (+/- 1 SD) tissue factor activity of 1,491 +/- 2,160 units/5 X 10(5) cells, as compared with a mean of 480 units (range, 140 to 1,000 units) for normal control subjects. The same cells had a mean plasma Factor VII equivalent of 4.7 ng/10(6) cells, as compared with 0.81 ng/10(6) cells (range, 0.2 to 2.0 ng) for the normal control subjects. The enhanced activity correlated with disease activity as judged by radiographic stage: only patients with Stage II or Stage III disease had consistently elevated procoagulant activity. There was no correlation of procoagulant activity with the percentage of lymphocytes in the alveolar fluid. Cells from patients with idiopathic pulmonary fibrosis also had increased tissue factor (mean, 2,980 +/- 2,619 units) but less consistently elevated Factor VII. There was considerable variation in both procoagulant activity and cell differentials between lavage sites in 10 patients in whom 2 separate lobes were studied concurrently. In addition, we examined the plasminogen activator (PA) activities of lavaged cells and concentrated alveolar fluids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Results of a phase I/II trial of recombinant human granulocyte- macrophage colony-stimulating factor in very low birthweight neonates: significant induction of circulatory neutrophils, monocytes, platelets, and bone marrow neutrophils

Neonates, especially those of very low birthweight (VLBW), have an increased risk of nosocomial infections secondary to deficiencies in development. We previously demonstrated that granulocyte-macrophage colony-stimulating factor (GM-CSF) production and mRNA expression from stimulated neonatal mononuclear cells are significantly less than that from adult cells. Recombinant murine GM-CSF administration to neonatal rats has resulted in neutrophilia, increased neutrophil production, and increased survival of pups during experimental Staphylococcus aureus sepsis. In the present study, we sought to determine the safety and biologic response of recombinant human (rhu) GM-CSF in VLBW neonates. Twenty VLBW neonates (500 to 1,500 g), aged < 72 hours, were randomized to receive either placebo (n = 5) or rhuGM-CSF at 5.0 micrograms/kg once per day (n = 5), 5.0 micrograms/kg twice per day (n = 5), or 10 micrograms/kg once per day (n = 5) given via 2-hour intravenous infusion for 7 days. Complete blood counts, differential, and platelet counts were obtained, and tibial bone marrow aspirate was performed on day 8. Neutrophil C3bi receptor expression was measured at 0 and 24 hours. GM-CSF levels were measured by a sandwich enzyme-linked immunosorbent assay at 2, 4, 6, 12, and 24 hours after the first dose of rhuGM-CSF. At all doses, rhuGM-CSF was well tolerated, and there was no evidence of grade III or IV toxicity. Within 48 hours of administration, there was a significant increase in the circulating absolute neutrophil count (ANC) at 5.0 micrograms/kg twice per day and 10.0 micrograms/kg once per day, which continued for at least 24 hours after discontinuation of rhuGM-CSF. When the ANC was normalized for each patient's first ANC, there was a significant increase in the ANC on days 6 and 7 at each dose level. By day 7, all tested doses of rhuGM- CSF resulted in an increase in the absolute monocyte count (AMC) compared with placebo-treated neonates. In those receiving rhuGM-CSF 5.0 micrograms/kg twice per day, there was additionally a significant increase in the day 7 and 8 platelet count. Tibial bone marrow aspirates demonstrated a significant increase in the bone marrow neutrophil storage pool (BM NSP) at 5.0 micrograms/kg twice per day and 10.0 micrograms/kg once per day. Neutrophil C3bi receptor expression was significantly increased 24 hours after the first dose of rhuGM-CSF at 5.0 micrograms/kg once per day. The elimination half-life (T1/2) of rhuGM-CSF was 1.4 +/- 0.8 to 3.9 +/- 2.8 hours.(ABSTRACT TRUNCATED AT 400 WORDS)