title: T lymphocyte indifference to extrathymic islet allografts.
abstract: Although the deletion of self-reactive T cells maturing in the thymus is well documented, the nature of tolerance to Ags expressed exclusively on peripheral (extrathymic) tissues is less clear. Numerous studies have examined T cell reactivity to transgene-encoded Ags expressed in the periphery through tissue-specific promoters. These studies have yielded varied results concerning the degree and nature of tolerance induced to these Ags, ranging from T cell clonal deletion or inactivation to clonal "ignorance" of the peripheral transgene-encoded Ag. Furthermore, the relationship of these findings to the generation and maintenance of transplantation tolerance to extrathymic tissue allografts remains unclear. Whereas transgenic studies represent a developmental form of tolerance, grafted tissues are introduced into adult, nontolerant recipients. To relate these two model systems, we determined whether extrathymic tissue allografts could induce a developmental form of tolerance. As a model of extrathymic alloantigen expression, pancreatic islet allografts, depleted of donor APCs, were established in the periphery of severe combined immune-deficient (SCID) mice. We then examined the potential donor reactivity of adoptively transferred bone marrow-derived T cell precursors maturing in the presence of the established peripheral allograft. Such T cells were neither activated nor tolerized either in vitro or in vivo, suggesting that T cells are indifferent to Ags expressed by extrathymic islet allografts when presented in the absence of a second costimulatory signal.
authors.affiliation: Barbara Davis Center for Childhood Diabetes, University of Colorado Health Sciences Center, Denver 80262, USA.
authors.forename: M
authors.initials: M
authors.lastname: Coulombe
authors.forename: R G
authors.initials: RG
authors.lastname: Gill
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000938:Antigen-Presenting Cells / Q000276:immunology / Q000637:transplantation; D016026:Bone Marrow Transplantation; D002478:Cells, Cultured; D007108:Immune Tolerance; D016381:Islets of Langerhans Transplantation / Q000276:immunology*; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology*; D016042:Transplantation, Heterotopic / Q000276:immunology*; D014184:Transplantation, Homologous