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Biomedical subjects

P Seiler

Publications and source records attributed to P Seiler.

At least 37 records · Page 2Linked to original sources
PubMed1997

Reduced incidence and delayed onset of diabetes in perforin-deficient nonobese diabetic mice.

To investigate the role of T cell-mediated, perforin-dependent cytotoxicity in autoimmune diabetes, perforin-deficient mice were backcrossed with the nonobese diabetes mouse strain. It was found that the incidence of spontaneous diabetes over a 1 yr period was reduced from 77% in perforin +/+ control to 16% in perforin-deficient mice. Also, the disease onset was markedly delayed (median onset of 39.5 versus 19 wk) in the latter. Insulitis with infiltration of CD4(+) and CD8(+) T cells occurred similarly in both groups of animals. Lower incidence and delayed disease onset were also evident in perforin-deficient mice when diabetes was induced by cyclophosphamide injection. Thus, perforin-dependent cytotoxicity is a crucial effector mechanism for beta cell elimination by cytotoxic T cells in autoimmune diabetes. However, in the absence of perforin chronic inflammation of the islets can lead to diabetogenic beta cell loss by less efficient secondary effector mechanisms.

Animals↗
PubMed1997

Crucial role of marginal zone macrophages and marginal zone metallophils in the clearance of lymphocytic choriomeningitis virus infection.

Macrophages play a key role in the immune defense against pathogens. They control early invasion by antigen-unspecific phagocytosis of pathogens and act as professional antigen-presenting cells to induce antigen-specific T cell responses. To investigate the involvement of particular subsets of the splenic macrophages in an antiviral immune response, we selectively depleted mice of splenic marginal zone macrophages (MZM) and marginal zone metallophils (MM) using the clodronate liposome depletion technique. MZM- and MM-depleted mice were not able to control an infection with lymphocytic choriomeningitis virus (LCMV). In these mice, LCMV spread from the spleen to peripheral organs at an early phase of infection. The virus-specific cytotoxic T lymphocyte (CTL) response was induced initially, yet was exhausted in parallel with the overwhelming virus replication. These findings suggest that MZM and MM play a crucial role in the early control of a LCMV infection by preventing immediate virus spread to peripheral organs, but are not essential for the induction of the LCMV-specific CTL response.

Animals↗
PubMed1997

Antiviral immune responses in CTLA4 transgenic mice.

The role of B7 binding CD28 in the regulation of T- and B-cell responses against viral antigens was assessed in transgenic mice expressing soluble CTLA4-Hgamma1 (CTLA4-Ig tg mice) that blocks B7-CD28 interactions. The results indicate that transgenic soluble CTLA4 does not significantly alter cytotoxic T-cell responses against replicating lymphocytic choriomeningitis virus (LCMV) or vaccinia virus but drastically impairs the induction of cytotoxic T-cell responses against abortively replicating vesicular stomatitis virus (VSV). While the T-independent neutralizing immunoglobulin M (IgM) responses were within normal ranges, the switch to IgG was reduced 4- to 16-fold after immunization with abortively replicating VSV and more than 30-fold after immunization with an inert VSV glycoprotein antigen in transgenic mice. IgG antibody responses to LCMV, as detected by enzyme-linked immunosorbent assay and by neutralizing action, were reduced about 3- to 20-fold and more than 50-fold, respectively. These results suggest that responses in CTLA4-Ig tg mice are mounted according to their independence of T help. While immune responses to nonreplicating or poorly replicating antigens are in general most dependent on T help and B7-CD28 interactions, they are most impaired in CTLA4-Ig tg mice. The results of the present experiments also indicate that highly replicating viruses, because of greater quantities of available antigens and by inducing as-yet-undefined factors and/or cell surface changes, are capable of compensating for the decrease in T help caused by the blocking effects of soluble CTLA4.

Abatacept↗
PubMed1996

Specific cytotoxic T cells eliminate B cells producing virus-neutralizing antibodies [corrected].

In medically important infections with cytopathic viruses, neutralizing antibodies are generated within 6-14 days. In contrast, such protective antibodies appear late (50-150 days) after infection with immunodeficiency virus (HIV) and hepatitis B virus (HBV) in humans, or lymphocytic choriomeningitis virus (LCMV) in mice. However, during these infections, non-neutralizing antibodies appear much earlier. It has been proposed that T cells suppress antibody responses generally and against viruses in vitro. Here we show that the suppression of neutralizing-antibody-producing B cells by this non-cytopathic virus, and their subsequent destruction by virus-specific cytotoxic T cells. Such specific B-cell elimination that leads to a delay in neutralizing-antibody production could help to establish persistent virus infections by non-cytopathic viruses.

Animals↗
PubMed1995

The roles of perforin- and Fas-dependent cytotoxicity in protection against cytopathic and noncytopathic viruses.

In vitro, T cell-dependent cytotoxicity is mediated by two distinct mechanisms, one being perforin-, the other Fas-dependent. The contribution of both of these mechanisms to clearance of viral infections was investigated in mice for the non-cytopathic lymphocytic choriomeningitis virus (LCMV) and the cytopathic vaccinia, vesicular stomatitis (VSV) and Semliki forest (SFV) viruses. Clearance of an acute LCMV infection was mediated by the perforin-dependent mechanism without measurable involvement of the Fas-dependent pathway. For the resolution of vaccinia virus infection and for resistance against VSV and SFV, however, neither of the two pathways was required. These data suggest that perforin-dependent cytotoxicity mediated by T cells is crucial for protection against non-cytopathic viruses, whereas infections with cytopathic viruses are controlled by nonlytic T cell-dependent soluble mediators such as cytokines (IFN-gamma against vaccinia virus) and neutralizing antibodies (against VSV and SFV).

Alphavirus Infections↗
PubMed1995

Enzyme-linked immunosorbent assay for detection of antibody to lymphocytic choriomeningitis virus in mouse sera, with recombinant nucleoprotein as antigen.

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of antibody to lymphocytic choriomeningitis virus (LCMV) in mouse sera. This assay is based on recombinant LCMV nucleoprotein generated in a baculovirus system. Sera from experimentally and naturally infected as well as noninfected mice were tested, and the results were compared with those obtained from an established immunofluorescence assay (IFA) that uses infected cells as antigen. An excellent correlation was found; the ELISA specificity and sensitivity were calculated to be 100 and 95% respectively. Unlike the IFA, this ELISA does not require the handling of infective virus. It eliminates the need to work with a zoonotic agent in the laboratory while allowing effective screening of laboratory mouse populations for LCMV antibody.

Animals↗
PubMed1994

Cytotoxicity mediated by T cells and natural killer cells is greatly impaired in perforin-deficient mice.

Perforin-deficient mice have been generated by homologous recombination to determine whether the effects of CD8+ cytolytic T cells and natural killer cells are mediated by pore formation involving perforin. These mice are viable and fertile and have normal numbers of CD8+ T cells and natural killer cells which do not lyse virus-infected or allogeneic fibroblasts or natural killer target cells in vitro. The mice fail to clear lymphocytic choriomeningitis virus and they eliminate fibrosarcoma tumour cells with reduced efficiency. Perforin is therefore a key effector molecule for T-cell- and natural killer-cell-mediated cytolysis.

Amino Acid Sequence↗
PubMed1994

Effects of persistent chlorinated hydrocarbons on fertility and embryonic development in the rabbit.

The commercial polychlorinated biphenyl (PCB) formulation Aroclor 1260 (4 mg/kg body weight), technical grade dichlorodiphenyltrichloroethane (DDT; 3 mg) and Lindane (gamma-hexachlorocyclohexane; 0.8 mg) were administered orally, either separately or in combination, to sexually mature female rabbits three times per week for 12-15 weeks. Oviductal and uterine luminal fluid, cleavage stage embryos (day 1 post coitum), blastocysts (day 6), fetuses, exocoelic fluid and placentae (day 11) were analysed, firstly for chlorinated hydrocarbon residues, and secondly for embryonic and fetal development. The doses applied were well tolerated by the treated animals. PCB and DDT accumulated in uterine secretions (day 6) but not in oviductal luminal fluid (day 1). Both chlorinated hydrocarbons were found in preimplantation blastocysts. Residues in day 11 fetuses were 16- (DDT) or 18-fold (PCB) higher than in day 6 blastocysts. Significant amounts were also detected in placental tissue and in exocoelic fluid. A specific accumulation of the highly chlorinated biphenyl congener no. 180 was noted in fetuses, placentae and exocoelic fluid. The clear accumulation of the chlorinated hydrocarbon compounds in luminal fluid and embryonic tissue is contrasted by rather weak effects on fertility. No statistically significant differences between treated animals and controls were observed for fertilization rate and pre- and post-implantation (up to day 11 post coitum) losses. However, in females exposed to PCB, a 20% higher loss of blastocysts was noticed, as compared with controls (P > 0.05). This effect was shown on day 6 of embryonic development and may be due to the embryotoxic activities of PCB.

Animals↗
PubMed1994

Effects of persistent chlorinated hydrocarbons on reproductive tissues in female rabbits.

The female rabbit was used to study (i) accumulation of lipophilic chlorinated hydrocarbons in genital tract tissues and (ii) subsequent morphological and functional effects after long-term low-dose exposure. Polychlorinated biphenyl (PCB), 1,1-di(p-chlorophenyl)-2,2,2-trichloroethane (DDT) and gamma-hexachlorocyclohexane (gamma-HCH) (dosages: 4, 3 and 0.8 mg per kg body weight, respectively) and a combination of these three components (and dosages) were administered to sexually mature rabbits over a period of 12-15 weeks. The animals were killed shortly before and at various times after ovulation. Accumulation of chlorinated hydrocarbons was high in ovarian, oviductal and uterine tissues, in follicular fluid and clearly detectable in uterine secretions. In follicular fluid, the concentration and patterns of congeners and isomers of PCB and DDT were distinctly different from serum. DDT- and gamma-HCH-treated animals showed a significantly reduced ovulation rate (P < 0.002 and 0.05, respectively). During early pregnancy DDT decreased serum progesterone levels and changed the protein pattern of uterine secretion. Functional effects, however, were much less expressed compared with the highly significant accumulation of the persistent organochlorines in the genital tract.

Animals↗
PubMed1990

Rabbit small intestinal trehalase. Purification, cDNA cloning, expression, and verification of glycosylphosphatidylinositol anchoring.

alpha,alpha-Trehalase (EC 3.2.1.28), an intrinsic protein of intestinal brush-border membranes, was purified to homogeneity from rabbits. Partial amino acid sequences were determined. Two degenerate oligonucleotides based on the sequence of a CNBr peptide were employed in a polymerase chain reaction to amplify a 71-base pair fragment of trehalase DNA with rabbit intestine cDNA as a starting template. This fragment was used as a hybridization probe to isolate full length trehalase clones from a rabbit intestine cDNA bank. Sequence analysis revealed that trehalase comprises 578 amino acids, contains at the amino terminus a typical cleavable signal sequence, at the carboxyl terminus a rather hydrophobic region typical of proteins anchored via glycosylphosphatidylinositol, and four potential N-glycosylation sites. Trehalase has no sequence homologies with other sequenced brush-border glycosidases. Northern blot analysis revealed a 1.9-kilobase trehalase mRNA in small intestine and kidney, smaller amounts in liver, and none in lung. Southern blot analysis indicated the gene has a length of 20 kilobase pairs or less. Injection into Xenopus laevis oocytes of mRNA synthesized in vitro from a trehalase template resulted in the expression of trehalase activity several hundredfold above background. The trehalase activity was membrane-bound and could be solubilized upon digestion with phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis. This strongly suggests that rabbit small intestinal trehalase is anchored via glycosylphosphatidylinositol also when expressed in X. laevis oocytes.

Amino Acid Sequence↗
PubMed1983

5-Phenyl-1,3-dihydro-1,4-benzodiazepin-2-ones. Experimental verification of substituent constants.

The partition coefficient, pK-values and the angle of twist of the 5-phenyl ring of 65 5-phenyl-1,3-dihydro-1,4-benzodiazepin-2-ones were experimentally determined. Linear regression models were applied to examine existing additivity rules. The experimental and calculated values are mostly in good agreement. Systematic deviations confirm that, with the models commonly used, some of the substituent effects are not fully accounted for.

Benzodiazepinones↗
PubMed1982

Partition coefficients of 5-(substituted benzyl)-2,4-diaminopyrimidines.

The pK-values of 19 and the partition coefficients P of 79 5-benzyl-2,4-diaminopyrimidines substituted in the benzene moiety were experimentally determined. The results of a multiple regression analysis show that the partition coefficients cannot be calculated with reasonable accuracy starting from fragmental constants. Interactions between substituents can reduce P-values by an order of magnitude below those obtained by applying Hansch's and Rekker's models. Interaction terms between different substituents were calculated. Similar effects are to be expected for other poly-substituted aromatic compounds.

Chemical Phenomena↗
PubMed1981

Steric and lipophobic components of the hydrophobic fragmental constant.

Newly calculated increments of molar volumes and surface areas were compared with hydrophobic fragmental constants in an effort to establish a relationship between these parameters. For completely non-polar fragments, the hydrophobicity is directly and linearly related to the volume or surface area. In the case of most fragments, however, the hydrophobicity is found to result from two factors, namely, a) a volume- or surface-related lipophilicity, and b) a lipophobicity effect, designated. The physical meaning of this parameter is unclear at present and may be related to hydration effects. The parameter may be of interest in QSAR studies. This is illustrated by an example in which the combined use of V and discriminates between the steric and lipophobic contributions of the partition coefficient to the biological activity.

Chemical Phenomena↗