Impaired Post-Thymic Development of Regulatory CD4+25+ T Cells Contributes to Diabetes Pathogenesis in BB Rats

Abstract

One of the BB rat diabetes (diabetes mellitus (DM)) susceptibility genes is an Ian5 mutation resulting in premature apoptosis of naive T cells. Impaired differentiation of regulatory T cells has been suggested as one possible mechanism through which this mutation contributes to antipancreatic autoimmunity. Using Ian5 congenic inbred rats (wild-type (non-lyp BB) and mutated (BB)), we assessed the development of BB regulatory CD8−4+25+T cells and their role in the pathogenesis of DM. BB rats have normal numbers of functional CD8−4+25+Foxp3+ thymocytes. The proportion of CD25+ cells among CD8−4+ recent thymic emigrants is also normal while it is increased among more mature CD8−4+ T cells. However, BB CD8−4+25+Foxp3+ thymocytes fail to undergo homeostatic expansion and survive upon transfer to nude BB rats while Foxp3 expression is reduced in mature CD8−4+25+ T cells suggesting that these cells are mostly activated cells. Consistent with this interpretation, peripheral BB CD8−4+25+ T cells do not suppress anti-TCR-mediated activation of non-lyp BB CD8−4+25− T cells but rather stimulate it. Furthermore, adoptive transfer of unfractionated T cells from diabetic BB donors induces DM in 71% of the recipients while no DM occurred when donor T cells are depleted of CD8−4+25+ cells. Adoptive transfer of 106 regulatory non-lyp BB CD8−4+25+ T cells to young BB rats protects the recipients from DM. Taken together, these results demonstrate that the BB rat Ian5 mutation alters the survival and function of regulatory CD8−4+25+ T cells at the post-thymic level, resulting in clonal expansion of diabetogenic T cells among peripheral CD8−4+25+ cells.

A Functional Polymorphism of Ptpn22 Is Associated with Type 1 Diabetes in the BioBreeding Rat

“…The results of this analysis have been previously reported (4). Nonlymphopenic, ACI.1u, and BB Non-Lyp inbred strains that are homozygous for wild type Gimap5 have been previously described (28,29).…”

“…Therefore, this T cell subset was evaluated in Ptpn22 congenic 2BAa and 2BAb rat donors. It has previously been demonstrated that the Gimap5 null mutation of the BBDP strain severely compromises the function and survival of CD4 + 25 + Foxp3 + Tregs once they exit the thymus (29). To circumvent this problem, we generated induced Tregs (iTregs) from ex vivo naive CD4 + 25 2 T cells congenic for rat Ptpn22 as previously described (14,30).…”

“…The resultant cell population was sorted for high CD25 levels to enrich for Foxp3-expressing Tregs, which accounted for 60-65% of the total population. This subset enriched in Foxp3 + cells was subsequently used in the Treg suppression assay, as previously outlined (29).…”

“…Preparation of mononuclear cell suspensions and staining of cell surface and intracellular Ags were performed as previously described (29). Samples were acquired on a FACSCalibur flow cytometer (BD Biosciences, Mississauga, ON, Canada) and analyzed using FlowJo (Tree Star, Ashland, OR).…”

Wheat protein-induced proinflammatory T helper 1 bias in mesenteric lymph nodes of young diabetes-prone rats

“…The reasons why the gut of the BBdp rat is a site of wheat protein-induced CD4 + T cell proliferation are not known, but could be related to the low frequency of CD4 + CD25 + T regulatory cells and the increased frequency of antigen-presenting cells (Fig. 5) [46]. The development of enteropathy in the BBdp gut by as early as 30 days [10] could set the stage for the continuing inflammatory damage and increased permeability [11,47] that has been linked to diabetes outcome [48] and is reported to be diet-modifiable [14,47].…”