Infectious tolerance develops after intrathymic alloantigen-induced acceptance of rat heart allografts can be adoptively transferred

Combined intrathymic and intravenous injection of mesenchymal stem cells can prolong the survival of rat cardiac allograft associated with decrease in miR-155 expression

BACKGROUND

Mesenchymal stem cells (MSCs) have the potential to improve graft outcomes and promote allograft tolerance. In this study, we examined the effects and mechanism of combined intrathymic (i.t.) and intravenous (i.v.) injection of MSCs on the survival of transplanted hearts in a rat allograft model.

METHODS

Recipient Sprague-Dawley rats were transplanted with hearts from Wistar rats. Wistar rat MSCs were infused via i.t. or i.v. or combined i.t. and i.v. (i.t./i.v.) injection at designated intervals. In vitro mixed lymphocyte reaction assays were performed to assess the immunosuppressive capacity of MSCs. Mesenchymal stem cell surface markers and CD4+, CD25+, and Foxp3+ T-cells in the peripheral blood were detected using flow cytometry analysis. The expression of microRNAs and cytokines in graft infiltrating lymphocytes was analyzed by real-time polymerase chain reaction.

RESULTS

The MSCs cultured in vitro had multipotential differentiation capacity. Mixed lymphocyte reaction assays showed that donor-derived MSCs could not stimulate a proliferative response of recipient lymphocytes and could markedly suppress T-cell responses. Survival of the allografts was significantly prolonged by administration of i.t./i.v. injection of MSCs compared with controls, with a mean survival of 32.2 versus 6.5 d, respectively. Compared with the syngeneic groups posttransplant, miR-155 expression was significantly increased in the allogeneic group, and could be restored by injection of MSCs, especially i.t./i.v. injection of MSCs. Moreover, i.t./i.v. injection of MSCs decreased the level of interleukin (IL)-2 and interferon-gamma, but increased the levels of IL-4 and IL-10 in the allogeneic group. More important, i.t./i.v. injection of MSCs was the best way to increase the percentage of CD4+, CD25+, and Foxp3+ T-cell peripheral blood.

CONCLUSIONS

Our results indicated that i.t./i.v. injection of MSCs can prolong the survival of rat cardiac allograft, which may be associated with down-regulating miR-155 expression, a shift in the Th1/Th2 balance, and up-regulation of Treg cells expression.

Allopeptides and the alloimmune response

The inherent ability of the host immune system to distinguish between self- and non-self forms the basis of allorecognition. T lymphocytes constitute the most important effector arm of allorecognition. Here we describe the fundamentals of direct and indirect pathways by which allopeptides are presented to effector T cells. The nature of allopeptides presented along with tolerogenic strategies like altered peptide ligands and intra- or extra-thymic allopeptide inoculation are discussed. In addition, we speculate on the potential of regulatory T cells to modulate alloimmune responses.

Functional compartmentalization following induction of long-term graft survival with pregraft donor-specific transfusion

Long-term survival is achieved in rat recipients by pre-graft donor-specific blood transfusion. We characterized the immune compartments in long-term survivors and analyzed them for capacity to transfer tolerance and protect against chronic rejection. Splenocytes and spleen T cells from treated recipients transferred long-term graft survival to 100% of secondary recipients. In contrast, blood transferred graft survival to only 50% of recipients whereas blood T cells had no effect. An unaltered TCR repertoire, an increase in suppressive CD4+CD25+ T cells, a decrease in antidonor T-cell proliferative response and normal perforin-granzyme levels were the hallmarks of the spleen T cells. Blood T cells were characterized by a strongly altered CD8+ repertoire, normal CD4+CD25+ T cell number with unchanged antidonor T-cell proliferative response, an activated T-cell phenotype and an increase in perforin-granzyme levels. However, following the transfer of blood or spleen cells into secondary recipients, all grafts displayed chronic rejection. These findings provide evidence that distinct compartments play critical roles in DST recipients. Regulatory cells do not accumulate in blood, which appears to be a reservoir for cytotoxic T cells. Spleen T cells, which display a regulatory-like profile and transfer graft survival, are not able to prevent chronic rejection.

Papel das células T reguladoras no desenvolvimento de dermatoses

Células T, em particular as células T CD4+, têm sido associadas a muitos aspectos das doenças de pele. A evidência atual sugere, porém, que o papel dos linfócitos T CD4+ no desenvolvimento de inflamação cutânea excede o de ativador pró-inflamatório das células T de ação que dirigem a resposta imune. Subtipos de células T com capacidade reguladora, tais como Tregs CD4+CD25+high, têm sido identificadas. Observações recentes sugerem que em algumas doenças da pele a função dessas células está modificada. Portanto, o desenvolvimento e a função de Tregs na dermatologia são atualmente um tópico atraente devido a sua importância no controle da resposta do sistema imune contra tumores e doenças infecciosas, bem como inibindo o desenvolvimento de auto-imunidade e alergia. Assim, mecanismos reguladores defeituosos podem permitir a quebra da tolerância imune periférica seguida por inflamação crônica e doença. Detalham-se as anormalidades funcionais e a contribuição de diferentes subtipos de células T reguladoras no desenvolvimento de doenças dermatológicas nesta revisão. Acentuam-se os possíveis alvos terapêuticos e as modificações dos T reguladores causados por imunomoduladores usados no campo da dermatologia.