Biomedical subjects

T Norton

Publications and source records attributed to T Norton.

35 records · Page 2Linked to original sources

PubMed1997

In vitro positive selection of alpha beta TCR transgenic thymocytes by a conditionally immortalized cortical epithelial clone.

Development of mature CD4 and CD8 single-positive T cells requires a process known as positive selection, which depends on the specific recognition of self-peptide-MHC complexes on thymic stromal cells by immature CD4+CD8+ thymocytes. We have used an in vitro reaggregate system to study the positive selection of thymocytes by conditionally immortalized thymic epithelial clones. Thymocytes from mice transgenic for the F5 alpha beta TCR, specific for a peptide from the influenza nucleoprotein in the context of H-2Db, are positively selected in the H-2b MHC background, but fail to mature in mice expressing the H-2q haplotype. Development of embryonic day 15 F5 H-2q transgenic thymocytes was followed in reaggregate cultures supplemented with H-2b-expressing epithelial clones. A conditionally immortalized cortical epithelial clone, derived from H-2Kb-tsA58 transgenic mice, was found to be as efficient as freshly isolated thymic stromal cells in positively selecting CD8 transgenic thymocytes. In contrast, an H-2b-expressing kidney epithelial clone did not augment positive selection above background levels, implying that the effect of the thymic epithelial clone was not merely the presentation of selecting MHC molecules. Mature transgenic thymocytes generated in reaggregate cultures were able to differentiate into functionally competent cytotoxic T cells. This model provides an important in vitro system for the detailed study of the specific molecular interactions leading to positive selection of developing thymocytes.

Animals↗

PubMed1996

Tolerance in TCR/cognate antigen double-transgenic mice mediated by incomplete thymic deletion and peripheral receptor downregulation.

Influenza nucleoprotein (NP)-specific T-cell receptor transgenic mice (F5) were crossed with transgenic mice expressing the cognate antigenic protein under the control of the H-2Kb promoter. Double-transgenic mice show negative selection of thymocytes at the CD4+8+TCRlo to CD4+8+TCRhi transition stage. A few CD8+ T cells, however, escape clonal deletion, and in the peripheral lymphoid organs of these mice, they exhibit low levels of the transgenic receptor and upregulated levels of the CD44 memory marker. Such cells do not proliferate upon exposure to antigen stimulation in vivo or ex vivo, however, they can develop low but detectable levels of antigen-specific cytotoxic function after stimulation in vitro in the presence of IL-2.

Animals↗

PubMed1996

The programmed cell death of an immature thymocyte cell line transgenic for an alpha beta TCR and the c-myc proto-oncogene.

The c-myc proto-oncogene linked to the mouse Thy-1 gene transcriptional unit predisposes mice to development of thymic tumors consisting predominantly of immature CD4+ CD8+ cells. In an attempt to immortalize immature T cells expressing a known T-cell antigen receptor (TCR), Thy-1/c-myc transgenic mice were bred to alpha beta TCR transgenic mice (F5), and CD4+ CD8+ cell lines were established from thymic tumors in double-transgenic mice. These cells expressed high-level heat-stable antigen (HSA) and were able to undergo programmed cell death upon induction with steroids and CD3 cross-linking, but not with cognate peptide. In addition, one line had rearranged and transcribed endogenous TCR alpha and beta genes, in spite of the fact that transgenic alpha and beta genes were also expressed. Furthermore, we show that Thy-1/myc transgenic mice deficient in recombination activating gene-1 (RAG-1) do not develop tumors, in contrast to RAG-1-/- mice, which are also transgenic for both Thy-1/myc and the F5 TCR. This indicates that in order for thymocytes to be transformed by the Thy-myc transgene, they need to proceed to the double-positive stage.

Animals↗

PubMed1994

The biological clock that measures the mitotic life-span of mouse embryo fibroblasts continues to function in the presence of simian virus 40 large tumor antigen.

Normal mammalian fibroblasts cultured in vitro undergo a limited number of divisions before entering a senescent phase in which they can be maintained for long periods but cannot be induced to divide. In rodent fibroblasts senescence can be prevented by expression of simian virus 40 large tumor antigen (T antigen). Cells expressing T antigen can proliferate indefinitely; however, such cells are absolutely dependent upon continued expression of T antigen for maintenance of growth; inactivation of T antigen results in a rapid and irreversible entry into a postmitotic state. To determine when, after the initial expression of T antigen, fibroblasts become dependent upon it for continued growth, we serially cultivated embryonic fibroblasts prepared from H-2Kb-tsA58 transgenic mice. We show that these fibroblasts become dependent upon T antigen for maintenance of proliferation only when their normal mitotic life-span has elapsed and that the biological clock that limits the mitotic potential continues to function normally, even in cells expressing this immortalizing gene. Our results suggest that random accumulation of cellular damage is unlikely to be the factor that limits fibroblast division but support the hypothesis that senescence is regulated via a genetic program.

Animals↗

PubMed1993

Positive and negative selection in transgenic mice expressing a T-cell receptor specific for influenza nucleoprotein and endogenous superantigen.

A transgenic mouse was generated expressing on most (> 80%) of thymocytes and peripheral T cells a T-cell receptor isolated from a cytotoxic T-cell clone (F5). This clone is CD8+ and recognizes alpha alpha 366-374 of the nucleoprotein (NP 366-374) of influenza virus (A/NT/60/68), in the context of Class I MHC Db (Townsend et al., 1986). The receptor utilizes the V beta 11 and V alpha 4 gene segments for the beta chain and alpha chain, respectively (Palmer et al., 1989). The usage of V beta 11 makes this TcR reactive to Class II IE molecules and an endogenous ligand recently identified as a product of the endogenous mammary tumour viruses (Mtv) 8, 9, and 11 (Dyson et al., 1991). Here we report the development of F5 transgenic T cells and their function in mice of the appropriate MHC (C57BL/10 H-2b, IE-) or in mice expressing Class II MHC IE (e.g., CBA/Ca H-2k and BALB/c H-2d) and the endogenous Mtv ligands. Positive selection of CD8+ T cells expressing the V beta 11 is seen in C57BL/10 transgenic mice (H-2b). Peripheral T cells from these mice are capable of killing target cells in an antigen-dependent manner after a period of in vitro culture with IL-2. In the presence of Class II MHC IE molecules and the endogenous Mtv ligand, most of the single-positive cells carrying the transgenic T-cell receptor are absent in the thymus. Unexpectedly, CD8+ peripheral T-cells in these (H-2k or H-2d) F5 mice are predominantly V beta 11 positive and also have the capacity to kill targets in an antigen-dependent manner. This is true even following backcrossing of the F5 TcR transgene to H-2d scid/scid mice, in which functional rearrangement of endogenous TcR alpha- and beta-chain genes is impaired.

Animals↗

PubMed1992

Thymic depletion and peripheral activation of class I major histocompatibility complex-restricted T cells by soluble peptide in T-cell receptor transgenic mice.

Injection of mice transgenic for a class I major histocompatibility complex-restricted T-cell receptor with a soluble peptide antigen from influenza virus nucleoprotein results in clonal depletion of double-positive immature thymocytes in the thymus and activation of mature T cells in the periphery, accompanied by a transient up-regulation of the T-cell receptor and CD3 and CD8 coreceptor molecules.

Animals↗

PubMed1992

Surgical management of perilymphatic fistulas: a Portland experience.

A comprehensive review of our series of surgical perilymphatic fistula (PLF) repairs, as well as a review of published results from other otologists, suggested an unacceptably high rate of postoperative PLF recurrence. Some recurrences were related to specific events (i.e., coughing, strenuous activity, Valsalva-type maneuvers). However many cases had no apparent cause. Rather, the patients' symptoms recurred spontaneously, and at reoperation the graft was seen to have not "taken," suggesting graft failure rather than "patient failure." After a critical evaluation of current PLF surgical procedures and state-of-the-art concepts of wound healing, we developed a new surgical technique for PLF closure. Combining the use of laser graft-site preparation, an autologous fibrin glue "buttress," and a program of postoperative activity restriction, the new procedure allowed us to achieve statistically significant improvements in graft retention and surgical outcome, with recurrences dropping from 27 percent to 8 percent. In addition, complete resolution or significant symptomatic improvement occurred in 89 percent of patients with vertigo and/or dizziness and in 84 percent with disequilibrium. We conclude that this new surgical technique is an important addition to the otologic surgeon's arsenal for PLF management.

Adolescent↗

PubMed1991

Surgical management of perilymph fistulas. A new technique.

A wide range of recurrence rates (21% to 47%) for perilymph fistula repairs have been reported in the otology literature. An improved surgical technique developed at the Portland (Ore) Good Samaritan Hospital and Medical Center Neurotology Department was used to repair perilymph fistulas in 58 patients from October 1986 to October 1988. Our recurrence rate was reduced from 27% in a 1982-1985 study to 8% in our study. At 1 year postoperatively, improvements in disequillibrium, dizziness, and vertigo were comparable with results of older surgical techniques. Functional outcomes were also good: 83% of patients returned to normal activities of daily living, and 71% also returned to school or resumed gainful employment outside the home.

Adolescent↗

PubMed1982

A double-blind crossover study of the effect of loperamide hydrochloride and codeine phosphate on ileostomy output.

Loperamide hydrochloride (4 mg t.d.s.) was compared with codeine phosphate (60 mg t.d.s.) in a double blind crossover study of patients with loose output from their ileostomies. Both drugs significantly decreased the daily output and water content of ileostomy fluid. Daily losses of sodium and potassium were less when the patients were treated with loperamide. Loperamide was also associated with less side effects. It is concluded that loperamide hydrochloride was more effective in the treatment of ileostomy diarrhoea than codeine phosphate. In this group of patients those with the highest outputs from their ileostomies benefited most from this treatment.

Adult↗

PubMed1976

Radiology of suprasellar ectopic pinealoma.

The radiographic and clinical findings in twenty-three recently reported cases of suprasellar ectopic pinealoma are reviewed and three previously unreported cases are described. It is concluded that suprasellar calcification is extremely rare; enlargement of the sella turcica was present in approximately 20 to 30 per cent, none demonstrated elevation of the anterior cerebral artery. Pneumography may show a smooth or irregular filling defect in the anterior part of the third ventricle. In one of the new cases there was an isotope uptake in the suprasellar region. The differential diagnosis and other clinical data are also discussed.

Adolescent↗

PubMed1974