PubMed Health⌕ Search

Biomedical subjects

S Schwender

Publications and source records attributed to S Schwender.

33 records · Page 2Linked to original sources
PubMed1993

Resident macrophages (ramified microglia) of the adult brown Norway rat central nervous system are constitutively major histocompatibility complex class II positive.

A flow cytometric phenotype for isolated adult central nervous system (CNS) ramified microglia was previously defined (CD45low CD11b/c+) in the Lewis strain rat, that clearly distinguished these cells from all blood-derived leucocytes, the latter being CD45high. Consistent with the reported lack of major histocompatibility complex (MHC) expression in the CNS, isolated microglia were mostly MHC class II-. Employing these phenotypic criteria, we now show that a proportion of microglia in Brown Norway (BN) strain rats are constitutively MHC class II+. In spinal cord, up to 25% of microglia are distinctly positive and most have some level of expression. In situ staining of MHC class II+ microglial cells in BN rats indicates that positive cells are typical of ramified microglia on the grounds of both morphological appearance and anatomical location. In Lewis (LEW) rats, the few MHC class II-expressing cells isolated from the normal CNS are CD45high blood-derived cells and not resident microglia. After infection of both LEW and BN rats with a neurotropic murine hepatitis virus (MHV-JHM), MHC class II was rapidly upregulated on microglia in the BN but not in the LEW strain. In the latter, inflammatory cells were the predominant MHC class II-expressing population. Nevertheless, most microglia in the LEW strain could, after some delay, be induced to express MHC class II after transfer of an experimental autoimmune encephalomyelitis (EAE)-inducing encephalitogenic T cell line. Paradoxically, strains resistant to EAE (exemplified by the BN) contained more constitutive MHC class II-expressing microglia than susceptible ones, when a variety of strains were examined. The results clearly establish that the normal CNS may contain MHC class II-expressing cells that are a resident rather than a transient blood-derived population. It is significant that this expression is strain related, but there is no evidence that microglial cell constitutive MHC class II expression predisposes to EAE susceptibility.

Animals↗
PubMed1992

Human immunodeficiency virus infection in microglia: correlation between cells infected in the brain and cells cultured from infectious brain tissue.

In acquired immunodeficiency syndrome, the lesions of the central nervous system in association with the human immunodeficiency virus are thought to be related to an infection of microglia, although no studies are available in which cultured and physiological characteristics of microglia cells infected in vivo have been examined. In this report, we used brain tissue from a child dying of human immunodeficiency virus infection and show that microglia cells were the main cell population being infected. Moreover, isolated macrophage-like cells from fresh brain material revealed a close resemblance to peripheral blood macrophages in their content of surface and intracellular antigens. No virus particles or viral antigens were produced by these cells during the first week of cultivation. Productive infection was readily apparent, however, by day 30. This finding illustrates the slow nature of the virus life cycle in these cells and the minimal cytopathology that accompanied the infection.

Brain↗
PubMed1991

Isolation and direct characterization of resident microglial cells from the normal and inflamed central nervous system.

In addition to the major population of infiltrating leukocytes recovered from inflamed rat central nervous system (CNS), all of which expressed high levels of leukocyte common antigen CD45, many cells were coisolated that were MRC OX42+ (complement receptor 3/CD11b) but expressed low-to-moderate levels of CD45 and major histocompatibility complex (MHC) class I molecules. Most cells from normal CNS, in contrast, lay within this latter, CD45low population. From previous in situ immunohistochemical studies, the fortuitously isolated CD45low cells were probably resident (ramified) microglia. Using irradiation chimeras, we show that resident microglia respond to inflammation by upregulating CD45, CD4, and MHC class I molecules with a minority of these cells increasing their expression of MHC class II molecules. A 3- to 4-fold increase in the number of microglia isolated from inflamed CNS provided indirect evidence that the cells had proliferated. In normal CNS, a very small population of blood-derived CD45high-expressing cells are present; most MHC class II expression is associated with these few cells and not with the resident microglia.

Animals↗
PubMed1991

Major histocompatibility complex-expressing nonhematopoietic astroglial cells prime only CD8+ T lymphocytes: astroglial cells as perpetuators but not initiators of CD4+ T cell responses in the central nervous system.

The potential of cells within the central nervous system (CNS) to initiate T lymphocyte responses is not known and was the subject of this study. Using the ability of virgin T lymphocytes to proliferate in a primary response to allogeneic determinants on antigen-presenting cells (APC), we have examined the capacity of major histocompatibility complex (MHC)-expressing astroglial cells to act as stimulators of primary and secondary T cell responses. Neither freshly isolated astrocytes nor primary astrocyte cultures pretreated with interferon gamma (IFN-gamma) to upregulate MHC class I and II expression stimulated unfractionated lymph node (LN) cell populations in the primary mixed lymphocyte reaction. In mixing experiments, astrocytes did not inhibit the T cell response to allogeneic LN stimulators. Purified responder CD4+ T cells also were not stimulated to proliferate or secrete interleukin 2 (IL-2) by MHC class I- and II-expressing astrocytes. In contrast to their inability to stimulate virgin, alloreactive CD4+ T cells, astrocytes were able to specifically stimulate an alloreactive CD4+ T cell line. Unprimed CD8+ T cells, however, exhibited some weak autonomous proliferation to astrocyte stimulators but this response was only substantial in the presence of exogenous IL-2, the latter predominantly being a CD4+ T cell product. Those CD8+ T cells responding in the presence of IL-2 were mainly T cell receptor alpha/beta+ IL-2 receptor (alpha chain)+, and a majority had shifted from high to low CD45R expression. Given the virtual dependence of CD8+ T cells in these studies, on CD4+ T cell help, and the complete absence of activation of this latter subset by astrocytes, it is clear that in the context of this resident CNS cell, further activation of either T cell subset by astrocytes within the CNS can only follow priming by another type of APC. The implications of these results for the induction of T cell responses in the CNS are discussed.

Animals↗
PubMed1991

The pathogenic role of virus-specific antibody-secreting cells in the central nervous system of rats with different susceptibility to coronavirus-induced demyelinating encephalitis.

The humoral immune response in the central nervous system (CNS) of susceptible Lewis (LE) rats and resistant Brown Norway (BN) rats was analysed after intracerebral infection with the murine coronavirus JHM (MHV4). The subclinical course of the infection in BN rats was characterized by an early rise of neutralizing antibodies in the cerebrospinal fluid (CSF) 7 days post-infection. At this time in LE rats, neutralizing antibodies were not detectable in the CSF and the animals developed neurological signs of infection. Subsequently, LE rats recovered from disease. This process was accompanied by increasing titres of virus-neutralizing antibodies. Within the CNS parenchyma of both rat strains, equivalent numbers of IgM-secreting cells were detected. However, in BN rats, virus-specific IgG secreting cells appeared earlier and in higher numbers. Moreover, based on the size of zones of antibody secreted by single cells in the Spot-ELISA assay, it appeared that cells from BN rats secreted IgG antibody of higher affinity. These data suggest that early maturation of antiviral antibody responses in the resistant BN rat probably restricts the spread of viral infection to small foci within the CNS, resulting in a subclinical level of primary demyelination. In contrast, the absence of neutralizing antibodies in the susceptible LE rats favours spread of the virus throughout the CNS, resulting finally in severe neurological disease.

Animals↗
PubMed1991

Population dynamics of lymphocyte subsets in the central nervous system of rats with different susceptibility to coronavirus-induced demyelinating encephalitis.

The inflammatory response in the central nervous system (CNS) of rats with differing susceptibility to demyelinating encephalitis induced by coronavirus MHV4 was characterized. Topographical maps showing the arrangement of infiltrating lymphocyte subsets in virus-infected tissue were developed by digital-image processing of immunohistologically stained CNS sections. The kinetics of the inflammatory process was evaluated by flow-cytometry on lymphocytes isolated from the CNS. Cumulative data obtained with these two techniques demonstrated the following features. In susceptible Lewis (LE) rats, viral antigens were disseminated throughout the CNS, including spinal cord. Onset as well as recovery from neurological disease was associated with a steep rise of infiltrating CD8+ T cells, which localized in close contact to virus-infected cells. Accompanying convalescence was a slight increase in B(OX33+) cells in the CNS and the accumulation of immunoglobulin-containing cells in the centre of virus-infected areas. In clinically resistant Brown Norway (BN) rats, virus-infected cells were mainly restricted to small periventricular foci and the extent of lymphocyte infiltration was never as high as that found at any time during the course of infection in LE rats. There were striking differences in the CD8+ T-cell population compared to LE rats. Cells of this phenotype were identified in virus-affected areas of BN rats only early after infection, and their infiltration profile revealed much lower quantities than in the CNS of susceptible LE rats. Although the population dynamics of B(OX33+) lymphocytes were comparable in BN and LE rats, as determined by flow-cytometry, less immunoglobulin-containing B cells were detected in virus-infected areas of BN rats.

Animals↗
PubMed1990

Interaction of a protein with a palindromic sequence from murine rDNA increases the occurrence of amplification-dependent transformation in mouse cells.

muNTS1, an element isolated from the nontranscribed spacer of murine rDNA, increases the occurrence of amplification-dependent transformation in mouse cells when integrated into plasmid DNA containing a selectable marker (Wegner, M., Zastrow, G., Klavinius, A., Schwender, S., Müller, F., Luksza, H., Hoppe, J., Wienberg, J., and Grummt, F. (1989) Nucleic Acids Res. 17, 9909-9932). In an initial attempt to dissect muNTS1 into its structural components we localized part of the transformation increasing activity to a long AT-rich stretch from the 5' region which interacts with HMG-I. Here we identify a second element on muNTS1 which also stimulates the rate of amplification-coupled transformation in cis. It is found in the 3' region of muNTS1 and contains the 11-base pair palindrome ATGGCTGCCAT. It is conserved in the otherwise strongly divergent ribosomal NTS regions from mouse, rat, and man and is also found in the origin/enhancer region of human papovavirus JC. The palindromic sequence interacts specifically with proteins from mouse cell extracts. Protein-DNA interaction was dependent on the presence of zinc ions in the extract. Point-specific mutations within the palindrome reduced protein-DNA complex formation substantially and concomitantly abolished the ability to stimulate the frequency of transformation. The binding activity was purified and shown to consist of two polypeptides with molecular masses of 70 and 73 kDa.

Animals↗
PubMed1990

An amplification-promoting sequence from mouse genomic DNA: interaction with a trans-acting factor that also affects gene expression.

We previously identified murine DNA sequences that stimulate the amplification of cis-linked plasmid DNA in mouse cells under selective conditions (Holst et al., 1988). Here we focus on the structural features of one of these elements, the 229-bp element 5. The amplification-promoting activity was fully recovered from the middle part of element 5. The active region interacted in a sequence-specific way with a protein from nuclear extracts. Using footprinting analyses the binding region was characterized and subsequently shown to be functionally active as an amplification-promoting sequence, whereas a mutated binding site was inactive. Therefore, cis-acting element 5 functioned via interaction with a trans-acting factor. The same binding site was also active as a promoter element for RNA polymerase II transcription, because it efficiently reconstituted the activity of a truncated herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) gene promoter lacking the distal Sp1 binding site. Thus, the same protein seems to function in both RNA polymerase II transcription and DNA amplification. Possible relationships between both functions are discussed.

Animals↗
PubMed1989

Cis-acting sequences from mouse rDNA promote plasmid DNA amplification and persistence in mouse cells: implication of HMG-I in their function.

Searching for amplification promoting sequences within the murine rDNA cistrons, we isolated two elements from the nontranscribed spacer region. These 370 bp and 423 bp long cis-acting elements, referred to as muNTS1 and muNTS2, are localized 4.1 kb and 4.6 kb upstream the RNA polymerase I transcriptional start site. They contain ca. 50 bp long AT-rich sequences that strongly interact with a protein from nuclear extracts. The protein could be purified and identified as HMG-I. A synthetic oligonucleotide encompassing the AT-rich stretch from muNTS1 is able to substitute for the muNTS elements. A similar sequence from the nontranscribed spacer of rat has previously been reported to be important for the function of the RNA polymerase I enhancer (1). Therefore the interaction of HMG I with the muNTS elements may play a role both in the stimulation of DNA amplification and transcription.

Amino Acid Sequence↗
PubMed1988

Murine genomic DNA sequences replicating autonomously in mouse L cells.

Plasmids that replicate autonomously in mouse L cells were constructed by inserting random genomic DNA fragments from Ltk- cells into a plasmid containing the HSV-1 thymidine kinase gene with a truncated low-efficiency promoter. HAT resistance was used as a selective marker. The presence of free plasmids in the DNA of transformants was demonstrated by hybridization with a specific plasmid probe, by electron microscopic visualization of circular DNA, and by recovering these plasmids by E. coli transformation. Nineteen different DNA fragments were isolated. They were characterized as murine autonomously replicating sequences by Mbol restriction endonuclease sensitivity, by bromodeoxyuridine substitution, by copy number determination, and by segregation analysis. Sequence analysis of the inserts of nine plasmids revealed a conserved element of 12 bp (CTCATGAGAGGCCAA) in five out of nine autonomously replicating sequences.

Acetyltransferases↗