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Biomedical subjects

U Gross

Publications and source records attributed to U Gross.

At least 127 records · Page 7Linked to original sources
PubMed1995

Monoclonal rat antibodies directed against Toxoplasma gondii suitable for studying tachyzoite-bradyzoite interconversion in vivo.

We previously reported the in vitro analysis of stage differentiation of Toxoplasma gondii in murine bone marrow-derived macrophages. The purpose of this study was to generate monoclonal rat antibodies that might be suitable for investigating tachyzoite-bradyzoite interconversion in vivo with the murine model. Immunization of Fischer rats with cysts of T. gondii NTE resulted in the generation of seven monoclonal antibodies of the immunoglobulin G2a, G2b, or M isotype, which were further characterized by the immunoblot technique, immunofluorescence assay, immunohistology, and immunoelectron microscopy. Immunoblots demonstrated specific reactivity of five monoclonal antibodies with proteins with molecular masses of 40, 52, 55, 60, 64, 65, and 115 kDa. One antibody (CC2) appeared to recognize a differently expressed antigen depending on the parasite stage, reacting with a 40-kDa molecule in tachyzoites and a 115-kDa antigen in bradyzoites and oocysts. Several other monoclonal antibodies were shown to be stage specific and to react in immunofluorescence assays or in immunoblots with either tachyzoites or bradyzoites. Kinetics of stage conversion in vitro could be monitored by immunofluorescence with two of these monoclonal antibodies. Preliminary immunohistological investigations of tissue sections from infected mice demonstrated the possible usefulness of these monoclonal antibodies for future in vivo studies on stage differentiation of T. gondii in the murine system.

Animals↗
PubMed1994

A comprehensive definition of the major antibody specificities in polyclonal rabbit antithymocyte globulin.

The potent immunosuppressive action of rabbit antithymocyte globulin (RATG) in allotransplant recipients has been recognized for many years. Some of the antibody specificities and immunoregulatory effects of RATG have been described, but a comprehensive definition of RATG components has not been reported previously. In this study, we have identified 23 specificities that are consistent among different clinical RATG batches and represent the major antibody specificities in RATG. These specificities were defined by immunoprecipitation/gel electrophoresis and also antibody blocking/flow cytometry methods. Titration studies performed for semiquantitative analysis of RATG antibodies showed that the antibodies present in highest titer were directed to CD6, CD16, CD18, CD28, CD38, CD40, and CD58 (titer > 1:4000), most of which are not T cell-specific antibodies. In contrast, the RATG antibodies that persisted the longest in vivo in the plasma of rhesus monkeys transplant recipients are antibodies to CD3, CD4, CD8, CD11a, CD40, CD45, CD54, and class I. These antibodies, which are directed at signal transduction and adhesion molecules, were present during the early period of lymphocyte recovery. We suggest that the persistence of these antibodies in vivo is directly related to the prolonged anergy of circulating T cells after RATG treatment and to the unusual potency and complex tapestry of immunological effects in transplantation.

Animals↗
PubMed1994

Biocompatibility of silver-coated polyurethane catheters and silver-coated Dacron material.

The local effects of silver-coated polyurethane catheters and Dacron material were compared to uncoated polyurethane catheters and Dacron material in a long-term implantation test using rabbits. The tissue-implant interaction was analysed by investigating the type and number of inflammatory cells, capillaries, fat tissue, the extent of fibrosis, thickness of the fibrous capsule, number and distribution of silver particles, and the size of giant cells. Silver-coated and uncoated materials displayed comparable signs of inflammation and tissue reaction.

Animals↗
PubMed1994

Further studies of veto activity in rhesus monkey bone marrow in relation to allograft tolerance and chimerism.

Infusing the DR-/dim fraction of bone marrow cells (BMC) from an allogeneic kidney donor into rabbit antithymocyte globulin-treated transplant recipients delivers a tolerogenic signal, leading to functional allograft tolerance in rhesus monkeys without additional drug therapy. Our updated results in an expanded series show a median 131-day graft survival of recipients given DR-/dim donor BMC with a 23% 1-year survival (P < 0.00001 vs. rabbit antithymocyte globulin controls). Removing DRbright cells from donor BMC appeared to have a significant effect (P < 0.05). We have further investigated the tolerogenic mechanism within the experimental framework of the veto hypothesis in this preclinical model. In limiting dilution assays, we demonstrated the donor specificity of clonal inactivation of CTL precursors (CTLp) after in vitro or in vivo exposure to DR-/dim donor BMC, confirming specific tolerance. Additionally, in vitro studies confirmed the allogeneic specificity of CTLp inactivation in 3-cell MLR assays; minimal bystander effects were seen on normal CTLp responses to third party stimulator cells, while CTLp responses to the BMC donor's cells were abrogated in the same cultures. BMC mediating the veto effect were found to be resistant to L-leucyl-L-leucine methyl ester (Leu-leu-OMe), which excluded BMC-mediated cytotoxicity by NK or lymphokine-activated killer cells, CTL, or activated macrophages. In contrast, veto activity was abolished if the BMC were pretreated with either high dose UV-B light irradiation, mitomycin, or gamma-irradiation, indicating that BMC contained a UV-B-sensitive precursor of the veto effector, and that a proliferative step separated the two. Irradiation of DR-/dim donor BMC or administration of cyclophosphamide after infusion of nonirradiated BMC prevented the tolerogenic effect. Only recipients given nonirradiated DR-/dim donor BMC demonstrated PBL chimerism, which associated with functional deletion of antidonor CTLp and duration of graft survival. The Leu-leu-OMe resistance and the other properties of the allogeneic monkey CD3- CD2+ CD8+ BMC subpopulation that exhibits tolerance-promoting activity in vitro and in vivo lead us to postulate that a donor BMC-derived precursor population, possibly a dendritic cell population, may induce allogeneic unresponsiveness in this model.

Animals↗
PubMed1994

Reduced replication of Toxoplasma gondii is necessary for induction of bradyzoite-specific antigens: a possible role for nitric oxide in triggering stage conversion.

Stage conversion between tachyzoites and bradyzoites of Toxoplasma gondii was investigated in vitro by using murine bone marrow-derived macrophages (BMMs) as host cells. Following infection of untreated BMMs with tachyzoites, spontaneous expression of bradyzoite-specific antigens (Bsa) occurred at low frequency with Toxoplasma strain-dependent ratios from 0.03 to 2%. As previously described for peritoneal macrophages, activation of tachyzoite-infected BMMs with gamma interferon (IFN-gamma) or lipopolysaccharide resulted in the induction of Bsa. When bradyzoites were used for infection, prolonged expression of Bsa could be observed in IFN-gamma-activated BMMs. The induction of Bsa expression seemed to be closely linked to parasite multiplication and increased to maximal values of 50 to 70% in intermediately activated macrophages with nitric oxide (NO) levels that allowed reduced parasite replication. Identical results in stage conversion were obtained when sodium nitroprusside was used as a source of exogenous NO, indicating that NO might be a molecular trigger of stage conversion. NO is reactive with iron-sulfur centers in proteins, thereby inhibiting proteins involved in the mitochondrial respiratory chain. Using oligomycin and antimycin A as inhibitors of mitochondrial function, growth inhibition of parasites and induction of Bsa were obtained. Since microglia are the functional correlates of macrophages in the central nervous system and inhibit T. gondii upon activation with IFN-gamma, a similar mechanism might be involved during cyst development in the brain.

Animals↗
PubMed1994

Two alleles of the gene encoding surface antigen P22 in 25 strains of Toxoplasma gondii.

A group of 25 strains of Toxoplasma gondii (4 mouse-virulent strains and 21 mouse-avirulent strains) were tested by immunoblot with 4 monoclonal antibodies (MAb) against surface antigen P22. Parasite lysates from only 12 strains were recognized by all 4 MAbs, while lysates from the remaining 13 strains (all avirulent) were not recognized by any of the 4 MAbs. Strains not recognized by the 4 MAbs were found to express an altered form of the P22 antigen. Sequencing of the P22 genes from 10 strains revealed only 2 alleles. One allele is identical to the gene from the virulent RH strain. The second allele carries 5 single nucleotide substitutions and an insertion of a GGT triplet when compared to the allele from the RH strain. Four of the 5 nucleotide changes result in amino acid substitutions and the triplet insertion results in an extra glycine residue. Four of the single base changes also result in restriction fragment length polymorphisms (RFLP). RFLP analysis of the P22 gene revealed only 2 patterns among the 25 strains. The allele of the P22 gene correlated with reactivity of the 4 MAbs to lysates of each strain. However, the allele of the P22 gene did not correlate with the virulence of each strain for mice.

Alleles↗
PubMed1994

Veto cells in transplantation tolerance.

Advances in immunosuppressive management for transplantation have improved graft survival. However, lasting success will probably depend on the induction of donor-specific unresponsiveness, avoiding chronic immunosuppressive drug therapy and its debilitating side effects. Tolerance strategies have been developed in rodents, but applicability to human organ transplantation has not been achieved. We have established a preclinical allogeneic kidney transplant model in unrelated outbred rhesus monkeys and have investigated a tolerance-inducing strategy in which posttransplant administration of rabbit antithymocyte globulin and infusion of a subpopulation of donor bone marrow cells yields long-term graft acceptance in the absence of chronic immunosuppressive drugs. Recent studies of the immunological mechanisms by which induction and maintenance of transplant tolerance is achieved in this model are presented within the framework of a veto hypothesis.

Animals↗
PubMed1993

Coexistence of heterogeneous populations of Toxoplasma gondii parasites within parasitophorous vacuoles of murine macrophages as revealed by a bradyzoite-specific monoclonal antibody.

The expression of bradyzoite-specific antigens (Bsa) of Toxoplasma gondii was studied in murine bone-marrow-derived macrophages that had previously been infected with tachyzoites. Growth conditions that allowed only restricted replication of Toxoplasma gondii resulted in heterogeneous populations; (1) Bsa-positive and Bsa-negative parasites could be observed within one parasitophorous vacuole (heterogeneous vacuole community), and (2) homogeneous Bsa-positive and homogeneous Bsa-negative vacuole communities coexisted within one macrophage host cell. These observations suggest that stage conversion does not seem to be a synchronous event for a vacuole community.

Animals↗
PubMed1993

Toxoplasma gondii: uptake of fetuin and identification of a 15-kDa fetuin-binding protein.

Lectin-binding studies demonstrated the presence of a 68-kDa glycoprotein in tachyzoites of Toxoplasma gondii harvested from P388D1 macrophage cell cultures but not in tachyzoites maintained in peritoneal cavities of NMRI mice. This protein was identified as the embryonic protein fetuin that regularly is contained in fetal calf serum, a component of cell-culture media. Uptake of fetuin by T. gondii was demonstrated by intracellular localization of this protein. As shown by latex agglutination and immunofluorescence, no specific binding of fetuin to the parasite's surface was detected. Using affinity chromatography on fetuin-agarose, it was demonstrated that fetuin bound specifically to a 15-kDa antigen of tachyzoites. As revealed by inhibition studies with sialic acid and the lectin Sambucus nigra agglutinin, the 15-kDa protein probably recognized glycan structures of fetuin.

Animals↗
PubMed1993

Comparison of a commercial enzyme immunoassay and an immunoblot technique for detection of immunoglobulin A antibodies to Toxoplasma gondii.

A commercial enzyme immunoassay (Platelia-Toxo IgA) and an immunoblot technique were compared with regard to their ability to detect IgA antibodies to the major surface protein P30(SAG1) of Toxoplasma gondii in 105 serum samples from patients with suspected or proven acquired toxoplasmosis. Comparison of the IgA-EIA with the immunoblot technique showed a concordance of 81.0%, with a sensitivity of 92.6% and a specificity of 78.4%. Due to its high sensitivity the IgA-EIA might detect IgA antibodies against Toxoplasma gondii at an early stage of infection, although excessive sensitivity could lead to detection of IgA antibodies for an extended period of time following the onset of infection.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Induction of bradyzoite-specific Toxoplasma gondii antigens in gamma interferon-treated mouse macrophages.

By using stage-specific monoclonal antibodies, an in vitro model has been developed to analyze the kinetics of expression of stage-specific antigens during the conversion process between tachyzoites and bradyzoites of Toxoplasma gondii. Following infection of murine macrophages with bradyzoites, the expression of bradyzoite-specific antigens declined, whereas the expression of tachyzoite-specific antigens increased during the first 72 h postinfection. Conversely, in gamma interferon-treated murine macrophages infected with tachyzoites, the inhibitory effect of gamma interferon on replication of parasites was accompanied by the induction of bradyzoite-specific antigens.

Animals↗
PubMed1993

Differentiation between mouse-virulent and -avirulent strains of Toxoplasma gondii by a monoclonal antibody recognizing a 27-kilodalton antigen.

Using a murine monoclonal antibody, we were able to differentiate between mouse-virulent and -avirulent strains of Toxoplasma gondii. Monoclonal antibody TB6G5 was reactive with eight clinical mouse-avirulent isolates but not with mouse-virulent laboratory strains RH and BK. The antibody-reactive antigen was identified by indirect immunofluorescence and immunoblot as a 27-kDa cytoplasmic protein expressed by tachyzoites as well as by bradyzoites.

Animals↗
PubMed1993

[Titanium implant as an alternative possibility in fusion of the cervical vertebrae--initial clinical experiences].

We report on our experience with the use of titanium for disc replacement in the cervical spine. In 52 patients a total of 55 titanium grafts were implanted. Follow-up examinations were available in 48 patients with an observation time of 14 month on average. Results of clinical-neurological examinations were excellent or good in 37 patients (77%), moderate in 9 cases (19%), while two patients (4%) showed poor outcome. Radiological follow-up examinations showed a correct position in 47 of the 48 patients. Incorrect position as observed in 1 case made operative revision necessary. According to our results, titanium grafts seem to be a useful alternative method as compared to conventional techniques of fusion. Essential advantages are simple handling, biocompatibility of the material as well as the solid bond achieved by the special qualities of the graft with respect to surface and form. Availability of different graft sizes allows tailored fusion.

Adult↗
PubMed1993

[Transient insulin-dependent diabetes mellitus with alpha-interferon therapy in chronic active hepatitis].

Since alpha-interferon has been introduced an efficient therapy of chronic active hepatitis has become available for the first time. Among some of the treated patients, however, alpha-interferon therapy causes typical side effects. Fever, chills, loss of weight, fatigue as well as arthralgia, myalgia, loss of concentration and hematologic side effects have to be mentioned in particular. We report the occurrence of a diabetes mellitus under alpha-interferon therapy. The metabolic disorder gradually normalized after 3 weeks of antidiabetic treatment, although the interferon medication had been continued. We consider this disorder to be an effect caused by the alpha-interferon. The underlying mechanism might be an insulin resistance or an autoimmunologic defect. For that reason, when administering alpha-interferon, we recommend regular analyses of the blood sugar level during the regular patient monitoring.

Alanine Transaminase↗
PubMed1993

Systematic serologic screening for toxoplasmosis in pregnancy.

OBJECTIVE: To determine which serologic method or combination of methods could most effectively identify acute toxoplasmosis during pregnancy and to assess whether systematic screening is practical and cost-effective. METHODS: Using basic serologic tests (direct agglutination test and immunosorbent agglutination assay), we screened 2104 women for toxoplasmosis. Immunoglobulin M (IgM)-reactive patients (IgM immunosorbent agglutination assay score of at least 3) were studied by differentiating serologic tests performed sequentially. RESULTS: Specific immunity was found in 874 pregnant women (41.6%); 155 (7.4%) were IgM-reactive and 12 (0.6%) had acute toxoplasmosis. Using a reduced immunosorbent agglutination assay score of at least 3 (normally a score of at least 6 is used), acute toxoplasmosis was identified in 11 women at their first prenatal visit, including two in whom acute infection would not have been detected by a score of 6 or more until 9 weeks later. One additional nonimmune patient with acute infection was identified only by follow-up serologic testing. CONCLUSION: Systematic screening followed by sequential differentiating serologic tests is practical and cost-effective for the diagnosis of acute toxoplasmosis during pregnancy.

Adult↗