CD4+CD25+ Regulatory T Cells Prevent Type 1 Diabetes Preceded by Dendritic Cell-Dominant Invasive Insulitis by Affecting Chemotaxis and Local Invasiveness of Dendritic Cells

Abstract

Development of type 1 diabetes (T1D) is preceded by invasive insulitis. Although CD4+CD25+ regulatory T cells (nTregs) induce tolerance that inhibits insulitis and T1D, the in vivo cellular mechanisms underlying this process remain largely unclear. Using an adoptive transfer model and noninvasive imaging-guided longitudinal analyses, we found nTreg depletion did not affect systemic trafficking and tissue localization of diabetogenic CD4+ BDC2.5 T (BDC) cells in recipient mice prior to development of T1D. In addition, neither the initial expansion/activation of BDC cells nor the number of CD11c+ or NK cells in islets and pancreatic lymph nodes were altered. Unexpectedly, our results showed nTreg depletion led to accelerated invasive insulitis dominated by CD11c+ dendritic cells (ISL-DCs), not BDC cells, which stayed in the islet periphery. Compared with control mice, the phenotype of ISL-DCs and their ability to stimulate BDC cells did not change during invasive insulitis development. However, ISL-DCs from nTreg-deficient recipient mice showed increased in vitro migration toward CCL19 and CCL21. These results demonstrated invasive insulitis dominated by DCs, not CD4+ T cells, preceded T1D onset in the absence of nTregs, and suggested a novel in vivo function of nTregs in T1D prevention by regulating local invasiveness of DCs into islets, at least partly, through regulation of DC chemotaxis toward CCL19/CCL21 produced by the islets.

The non-canonical NF-κB pathway is induced by cytokines in pancreatic beta cells and contributes to cell death and proinflammatory responses in vitro

“…CCL5 levels are elevated in serum of type 1 diabetic patients and contribute to the attraction of monocytes and neutrophils to the islets during insulitis [41,42]. CCL19 levels are also increased during diabetes development and enhance the migration of dendritic cells and macrophages to the islets [43,44]. CXCL12 levels are elevated in type 1 diabetes, and CXCL12 contributes to insulitis by stimulating the trafficking and homing of autoreactive B and T cells in animal models of type 1 diabetes [45,46].…”

In Vivo Monitoring of Inflammation and Regulation in Type 1 Diabetes

“…In addition, the change in cellular components in the islets may be due to the nTreg cells' ability to regulate the local migration of immune cells. In studies to address these questions, we found that, compared to that in control nTreg cell-sufficient mice, the accelerated invasive insulitis in nTreg cell-deficient recipient NOD/scid mice was predominated by a population of CD11c + dendritic cells, instead of by the adoptively transferred CD4 + BDC T cells (Lee et al, 2010). These results suggest that the presence of nTreg cells may inhibit islet-infiltration of CD11c + dendritic cells.…”

“…These studies showed that depletion of nTreg cells promoted progression and increased severity of insulitis in nTreg cell-deficient mice. Therefore, nTreg cell-deficient mice developed more severe invasive insulitis, compared to mostly periinsulitis found in control nTreg cell-sufficient mice (Lee et al, 2010). However, despite these differences, the nTreg cell-deficiency did not affect the number and activation status of BDC cells during the pre-diabetic stage.…”

“…In order to examine the role of nTreg cells in vivo in T1D and distinguish their effects on T1D onset during the four stages of insulitis development, we have used the novel animal models described in the previous sections for imaging analyses. In these studies, as part of our approaches, we have performed noninvasive BLI-guided in vivo analyses of BDC cell trafficking in real-time under varied conditions in the presence or absence of nTreg cells (Lee et al, 2010). In particular, in these studies we performed experiments to address the following questions: (1) Compared to nTreg cell-deficient mice, can the trafficking and systemic tissue localization of BDC cells be modulated by nTreg cells during development of T1D?…”

“…We then adoptively transferred these cells separately into NOD/scid recipient mice. Trafficking and tissue localization of the transferred Luc + BDC cells in the two cohorts were monitored until after the recipient mice that received Luc + CD4 + CD25 -(nTreg-deficient) BDC cells developed T1D (Lee et al, 2010). We have performed initial macro imaging analyses using BLI on recipient mice during the pre-diabetic stages.…”