Role of B cells in the pathogenesis of systemic sclerosis.

Systemic sclerosis (SSc) is an orphan disease characterized by progressive fibrosis of the skin and internal organs. Aside from vasculopathy and fibrotic processes, its pathogenesis involves an aberrant activation of immune cells, among which B cells seem to play a significant role. Indeed, B cell homeostasis is disturbed during SSc: the memory subset is activated and displays an increased susceptibility to apoptosis, which is responsible for their decreased number. This chronic loss of B cells enhances bone marrow production of the naïve subset that accounts for their increased number in peripheral blood. This permanent activation state can be explained mainly by two mechanisms: a dysregulation of B cell receptor (BCR) signaling, and an overproduction of B cell survival signals, B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL). These disturbances of B cell homeostasis induce several functional anomalies that participate in the inflammatory and fibrotic events observed during SSc: autoantibody production (some being directly pathogenic); secretion of pro-inflammatory and pro-fibrotic cytokines (interleukin-6); direct cooperation with other SSc-involved cells [fibroblasts, through transforming growth factor-ß (TGF-ß) signaling, and T cells]. These data justify the evaluation of anti-B cell strategies as therapeutic options for SSc, such as B cell depletion or blockage of B cell survival signaling.

Engraftable human neural stem cells respond to developmental cues, replace neurons, and express foreign genes.

Stable clones of neural stem cells (NSCs) have been isolated from the human fetal telencephalon. These self-renewing clones give rise to all fundamental neural lineages in vitro. Following transplantation into germinal zones of the newborn mouse brain they participate in aspects of normal development, including migration along established migratory pathways to disseminated central nervous system regions, differentiation into multiple developmentally and regionally appropriate cell types, and nondisruptive interspersion with host progenitors and their progeny. These human NSCs can be genetically engineered and are capable of expressing foreign transgenes in vivo. Supporting their gene therapy potential, secretory products from NSCs can correct a prototypical genetic metabolic defect in neurons and glia in vitro. The human NSCs can also replace specific deficient neuronal populations. Cryopreservable human NSCs may be propagated by both epigenetic and genetic means that are comparably safe and effective. By analogy to rodent NSCs, these observations may allow the development of NSC transplantation for a range of disorders.

Transgenic mice for interleukin 3 develop motor neuron degeneration associated with autoimmune reaction against spinal cord motor neurons.

Interleukin 3 (IL-3) stimulates the proliferation and differentiation of various haematopoietic progenitor cells. Recently, IL-3 and other cytokines were reported to exert a neurotrophic activity and to be associated with neurological disorders, suggesting their complex role in the central nervous system. We now show that overexpression of IL-3 in transgenic mice causes a motor neuron disease with several features of amyotrophic lateral sclerosis and progressive muscular atrophy. These animals exhibit hind limb paralysis at 7 months of age, associated with dendritic and axonal degeneration, loss of motor neurons in the spinal cord, and autoimmune reaction against these cells. We examined the effect of IL-3 on embryonic motor neurons survival in mixed spinal cord cultures. Our results suggest that motor neuronal degeneration is not directly triggered by the high level of expression of IL-3.

Biology and potential strategies for the treatment of GM2 gangliosidoses.

The GM2 gangliosidoses are a group of heritable neurodegenerative disorders caused by excessive accumulation of the ganglioside GM2 owing to deficiency in beta-hexosaminidase activity. Tay-Sachs and Sandhoff diseases have similar clinical phenotypes resulting from a deficiency in human hexosaminidase alpha and beta subunits, respectively. The lack of treatment for GM2 gangliosidoses stimulated interest in developing animal models to understand the molecular mechanisms underlying the various forms of this disease and to test new potential therapies. In this review, we discuss the molecular biology of GM2 gangliosidoses and the different strategies that have been tested in animal models for the treatment of this genetic disorder, including gene transfer and cell engraftment of neural stem cells engineered to express the hexosaminidase isoenzymes.

Expression of human beta-hexosaminidase alpha-subunit gene (the gene defect of Tay-Sachs disease) in mouse brains upon engraftment of transduced progenitor cells.

In humans, beta-hexosaminidase alpha-subunit deficiency prevents the formation of a functional beta-hexosaminidase A heterodimer resulting in the severe neurodegenerative disorder, Tay-Sachs disease. To explore the feasibility of using ex vivo gene transfer in this lysosomal storage disease, we produced ecotropic retroviruses encoding the human beta-hexosaminidase alpha-subunit cDNA and transduced multipotent neural cell lines. Transduced progenitors stably expressed and secreted high levels of biologically active beta-hexosaminidase A in vitro and cross-corrected the metabolic defect in a human Tay-Sachs fibroblasts cell line in vitro. These genetically engineered CNS progenitors were transplanted into the brains of both normal fetal and newborn mice. Engrafted brains, analyzed at various ages after transplant, produced substantial amounts of human beta-hexosaminidase alpha-subunit transcript and protein, which was enzymatically active throughout the brain at a level reported to be therapeutic in Tay-Sachs disease. These results have implications for treating neurologic diseases characterized by inherited single gene mutations.

In situ assessment of beta-hexosaminidase activity.

We have adapted two methods to evaluate the beta-hexosaminidase (HEX) enzymatic activity in cultured cells, based on the use of (i) the fluorogenic substrate 4-methylumbelliferyl-6-sulfo-2-acetamido-2- deoxy-beta-D-glucopyranoside (MU-GlcNAc-6-SO4) and (ii) the naphthol AS-BI-N-acetyl-beta-D-glucosaminide and hexazotized pararosaniline. We demonstrate that both methods could be used for the HEX isoenzymes by comparing wild-type and mutant human fibroblast cell lines, deficient for either an alpha or beta subunit from Tay-Sachs and Sandhoff patients. This in situ cytochemical assessment of HEX activity offers a rapid evaluation to study the expression of this enzyme in a heterogeneous cell population such as in gene transfer experiments.

Sequence of the promoter region of the mouse gene encoding ornithine aminotransferase.

We have isolated and sequenced the promoter region of the mouse gene (mOAT) encoding ornithine aminotransferase. A comparison of these mOAT sequences with previously reported sequences for the rat and human genes encoding OAT, rOAT and hOAT, respectively, revealed a 256-bp region flanking the transcription start point that is highly conserved between the three genes. This region contains sequence motifs resembling binding sites for general transcription factors, as well as other trans-acting regulatory proteins.

Correction of ornithine-delta-aminotransferase deficiency in a Chinese hamster ovary cell line mediated by retrovirus gene transfer.

Gyrate atrophy (GA) of the choroid and retina is an autosomal recessive chorioretinal degeneration, caused by deficiency of the mitochondrial matrix enzyme ornithine-delta-aminotransferase (OAT). This deficiency results in the accumulation of ornithine in the body fluids and leads to hyperornithinemia. Although the clinical phenotype is largely confined to the eye, OAT deficiency is a systemic disorder. With the final goal of applying gene therapy to this human genetic disease, we have established an in vitro model to test the correction of OAT enzymatic deficiency in mammalian cells, using OAT recombinant retroviruses. We report the construction of several Moloney murine leukemia virus (MoMLV)-based recombinant retrovirus vectors, in which the human OAT cDNA was placed under the transcriptional control of the mouse phosphoglycerate kinase (PGK) promoter or under the enhancer-promoter regulatory element derived from the MoMLV long terminal repeat (LTR). The retrovirus constructs were packaged in the PG13-GALV cell line and used to transduce C9, an OAT deficient cell line derived from Chinese hamster ovary cells (CHO-K1). We show that the recombinant retrovirus transfers the human OAT (hOAT) gene into C9. Expression of the hOAT gene in the transduced C9 deficient cell line exceeded the OAT mRNA level and enzymatic activity of endogenous human fibroblasts.

Retrovirus-mediated gene transfer and expression of human ornithine delta-aminotransferase into embryonic fibroblasts.

Ornithine delta aminotransferase (OAT) is a nuclear-encoded mitochondrial matrix enzyme that catalyzes the reversible transamination of ornithine to glutamate semialdehyde. In humans, genetic deficiency of OAT results in gyrate atrophy of the choroid and retina, a blinding chorioretinal degeneration usually beginning in late childhood. This disorder has been shown to be autosomal recessive, and is often caused by missense, nonsense, and/or frameshift mutations in the OAT gene. With the view of applying gene therapy, a Moloney murine leukemia virus (MoMLV)-based recombinant retrovirus vector has been constructed. The human OAT cDNA was placed under the control of the enhancer-promoter regulatory elements derived from the MoMLV long terminal repeat (LTR). The construct was transfected into the retroviral packaging cell lines GP + E - 86 and psi CRIP to produce virus particles. Supernatant from these OAT retrovirus producer cell lines were used to transduce mouse C57B1/6 embryonal fibroblasts. We showed that the recombinant retrovirus transfers the OAT gene to the recipient cells, which produce an OAT RNA transcript when analyzed by Northern blot. Western blot analysis and enzymatic assays confirmed the presence of an OAT polypeptide that has a high enzymatic activity in the transduced cell lines, even after a long period of time in vitro.

Immunochemical characterisation of antigens and growth inhibition of Fonsecaea pedrosoi by species-specific IgG.

Antigens of Fonsecaea pedrosoi, the most common agent of chromomycosis, were characterised by immunoprecipitation with a rabbit antiserum raised against the cell-protein extract and serum from an infected patient. Thirteen antigens were commonly detected and, as some of these antigens could be iodinated, they may be present in the fungal cell wall. Purified IgG from the rabbit antiserum was shown to produce a 50-60% inhibition of fungal growth. Some of the antigens characterised may be important in relation to the stimulation of protective immunity against chromomycosis.

Polypeptide antigens Mr 90,000 and 72,000 related to protective immunity against the blood form of Plasmodium falciparum in the squirrel monkey show stable characteristics in strains from different geographic origins.

Squirrel monkeys protected after vaccination with a particular protein fraction of Plasmodium falciparum elicit antibodies directed against two parasite proteins, Mr 90,000 and 72,000. We have used monoclonal antibodies and sera from protected monkeys to determine whether or not these polypeptides were polymorphic in 22 strains. In all the isolates studied, both polypeptides were conserved, as was the epitope defined by monoclonal antibody XIV/7 present on the Mr 90,000. Immunofluorescence of all strains showed the same pattern using 5 Mab produced against different fragments of the Mr 72,000 polypeptide from the FUP strain. All isolates examined were positive, indicating that this polypeptide was present in different strains and that the 5 epitopes were conserved. Peptide mapping of both the Mr 90,000 and 72,000 antigen purified from 3 different strains indicated that each antigen appeared to be conserved.

Changes in recognition of Plasmodium falciparum antigens by human sera depending on previous malaria exposure.

Naturally acquired immunity against Plasmodium falciparum malaria was analysed by immunoprecipitation and electrophoretic analysis of FUP-1 strain antigens by sera from individuals with different histories of exposure to malaria. Sera from individuals in the process of either acquiring natural resistance (from different age groups in a village of Upper Volta) or losing acquired resistance (adults travelling from hyperendemic areas of Africa to France) were compared. From electrophoretic patterns, it was apparent that two parasite peptides of MW 96 and 100 Kd were preferentially recognized by putatively resistant individuals. Analysis of the reactivity of adult sera from different parts of the world with FUP-1 antigens showed that there were no major geographically restricted antibody specificities. In particular, antibodies reactive with these two peptides were identified in sera of diverse geographic origins. These 96- and 100-Kd peptides of P. falciparum may therefore be antigens related to naturally acquired immune resistance and common to P. falciparum strains of different geographic origin.

In vivo time course of synthesis and processing of major schizont membrane polypeptides in Plasmodium falciparum.

A rapid method of separating membrane co-sedimentable and soluble components of Plasmodium infected erythrocytes is presented. We propose a nomenclature for major P. falciparum polypeptides, applicable to different isolates and based on their cellular location and stage specificity. For four of these polypeptides (185 kDa = Mp1; 120 kDa = Mp3; 76 kDa = Mp5; 90 kDa= Sp2) supposed to play a role in protective immunity, monospecific antibodies were available. We have studied their fate at the time of merozoïte release and reinvasion, and the possible correlations between these polypeptides, by pulse-chase experiments.

Plaque antibody selection: rapid immunological analysis of a large number of recombinant phage clones positive to sera raised against Plasmodium falciparum antigens.

A library of Plasmodium falciparum genomic DNA on the lambda gt11 phage vector was screened for clones positive to a rabbit serum raised against a purified fraction of P. falciparum proteins and a pool of sera from malaria patients. The positive clones were characterized with antibodies purified by the plaque antibody selection technique. This technique consist of purifying specific antibodies on a nitrocellulose filter blotted directly on a lawn of plaques of an antigen-producing phage clone. The purified antibodies are then used as a probe in a Western blot of parasite protein extract, for preliminary characterization of the clones. Using this method, two different clones coding for P. falciparum antigens were identified with the rabbit serum and about 20 with the human sera. This method can be of general use, i.e. it is not limited to parasite systems, and facilitates the immunological analysis and identification of a large number of clones.

Characterization of one polypeptide antigen potentially related to protective immunity against the blood infection by Plasmodium falciparum in the squirrel monkey.

We have previously demonstrated that squirrel monkeys vaccinated with a particular protein fraction of Plasmodium falciparum develop a protective immunity that is expressed at the humoral level by the presence of antibodies directed essentially against two parasite proteins. We have now isolated a mAb that recognizes one of these polypeptides of an apparent m.w. of 90,000 and an isoelectric point of 6.2. This parasite protein is synthesized in a short period of the asexual blood cycle corresponding to the mature tropho and early schizont stages, but is stable up to the end of the schizogony. By immunofluorescence analysis, the protein seems to be located essentially at the surface of the parasite and/or in the parasitophorous vacuole. The protein is degraded or modified in the process of reinvasion, because it was not detected in merozoites or in newly invaded RBC. Monoclonal antibody XIV-7 has no inhibitory effect against the parasite in vitro.

Protective immunization of the squirrel monkey against asexual blood stages of Plasmodium falciparum by use of parasite protein fractions.

We had previously shown that two polypeptides of Plasmodium falciparum are preferentially recognized by antibodies of resistant squirrel monkeys Saimiri sciureus. Free parasites were isolated from synchronized cultures on human erythrocytes initially inoculated with infected Saimiri erythrocytes. Crude extracts were prepared from mature schizont stages and electrophoresed on preparative NaDodSO4/polyacrylamide gels. Two groups of five monkeys were immunized with protein fractions eluted from the 75- and 100-kilodalton regions of the gels. Strong protection against challenge by the homologous strain of P. falciparum was induced in both groups. Analysis of specific anti-malarial antibodies revealed a homogeneous response of all the animals against a few polypeptides of the mature parasite.