Caracterització fenotípica i funcional de les cèl·lules T reguladores (naturals) en salut i malaltia (diabetis tipus 1)

Abstract

Natural regulatory T cells (nTreg) are lymphocytes generated during thymic selection and are part of the mechanisms that the immune system uses to keep homeostasis and control autoreactive responses that can lead to autoimmunity. nTreg are thymic emigrants that stably express FOXP3 thanks to epigenetical changes that take place during its maturation, which allow them to maintain their supressor functions. Besides, nTregs express the alpha chain of the IL-2 receptor, CD25, which confers them an activated phenotype. Other Treg markers are CTLA-4, GITR, CD127low and CCR6, but they are also induced in activated T cells during the immune response. Despite being an exclusive marker in the thymus, the intracelular expression of FOXP3 makes it non compatible with its use for Treg purification. Later it was described that activated human T cells can also express FOXP3 and even acquire a suppresive phenotype, although transitory. This fact, together with the absence of exclussive markers, makes difficult the use of these cells in immunotherapy. Thus, using several approaches, we have studied the phenotype of these cells in the thymus and in the periphery. After studing a numerous cohort of paediatric thymus (n=35) from donors aged from 2 days until 8 years old, we confirmed that the frequency of thymic populations changes with age, as previously described. Also, and for the first time, we observed that nTreg frequency diminishes with age. The phenotype of this population is stable during time, except for CD95, a member of the TNF family involved in apoptosis and cellular activation. The frequency of CD95+ cells in nTreg population increases with age, which suggests a higher susceptibility to CD95-mediated apoptosis, and that could explain the decrease of nTreg with time. Once nTregs are exported from the thymus to the periphery, they are mixed with activated T cells and memory T cells with which they share several markers. In our laboratory we searched for characteristical Treg molecules using a proteomic approach followed by a genetic expression analysis. From the comparison of thymic nTreg and peripheral Treg we defined galectin 3 as a marker acquired in periphery by nTregs. In activated Treg, functionally supressive, galectin 3 expression is found at similar levels as those of FOXP3 and CTLA-4, very characterical Treg markers. Finally, we studied this population in type 1 diabetes patients. We carried out an extensive phenotypical study in PBMCs from patients compared to donors that revealed a diminished proportion of GITR+ cells among nTregs. This defect did not affect to their suppressive ability, instead could be associated to an increased susceptibility to apoptosis.

Date of Award	28 Jan 2016
Original language	Catalan
Supervisor	Maria Merce Marti Ripoll (Director)