Regulatory T cells demonstrate significantly increased functions following stimulation with IL-2 in a Tim-3-dependent manner in intracranial aneurysms
Introduction
In healthy individuals, the CD4+CD25+Foxp3+ T regulatory (Treg) cells make up approximately 5% to 10% of total peripheral blood CD4+ T cells, and are critical to the induction of peripheral tolerance and the maintenance of immune homeostasis via multiple cell contact-dependent and contact-independent mechanisms [1]. The regulatory cytokine TGF-β is secreted by Treg cells and is critical to Treg-mediated suppression of self-reactive T cells. TGF-β blockade using a blocking antibody or the expression of a dominant negative TGF-β receptor could significantly reduce the capacity of Treg cells to mediate autoimmunity [2,3]. Treg cells upon peripheral stimulation may also express IL-10 and suppress T cell inflammation via IL-10-mediated mechanisms [4,5]. In addition, Treg cells express the inhibitory molecule CTLA-4, which activates immune suppressor IDO and downregulates CD80/CD86 on antigen-presenting cells via transendocytosis [6,7]. Another inhibitory molecule LAG-3, is found on both Treg cells and T regulatory type 1 (Tr1) cells, and is shown to activate an ITAM-mediated inhibitory pathway that suppresses dendritic cell maturation [8]. Moreover, by constitutively expressing the IL-2 receptor CD25, Treg cells competitively reduce the availability of IL-2 for other T cells.
Low-grade chronic inflammation is increasingly recognized to have a pathogenic role in the development of diseases such as obesity, osteoarthritis, type 2 diabetes, and cardiovascular diseases [9]. In intracranial aneurysm (IA), a condition characterized by a blood-filled sack formed by a localized thinning of the blood vessel, proinflammatory immune cells are extensively involved in its development and deterioration [10]. The IA lesions are infiltrated with neutrophils, monocytes, macrophages, and lymphocytes, which release cytokines and other immune mediators that upregulate the expression of adhesion molecules and chemokines, leading to further recruitment of immune cells [[11], [12], [13]]. Activated monocytes and macrophages can exacerbate aneurysms by promoting vasculature malformation via the expression of the matrix metalloproteinases (MMPs) that weaken the extracellular matrix [14]. Treg cells, on the other hand, were shown to reduce blood pressure, a risk factor in aneurysm formation, and lower the severity of experimental aneurysms in murine models via the production of IL-10 and TGF-β, and the suppression of TNF-α and MMPs [[15], [16], [17]]. These discoveries potentiate the use of Treg cells in therapeutics against IA and related cardiovascular diseases.
However, investigations from our group demonstrated that patients with intracranial aneurysms presented dysregulations in the Treg compartment, characterized by reduced frequency of Foxp3+ Treg cells, lower CTLA-4 expression, and lower IL-10 and TGF-β expression [18]. We further demonstrated that Treg cells from IA patients displayed a marked disability to upregulate Tim-3, a marker of highly functional Treg cells first discovered in the intratumoral environment [[19], [20], [21]]. In this study, we investigated potential ways of using IL-2 to improve Treg function in IA patients.
Section snippets
Participating volunteers
All experimental procedures were approved by the Ethics Committee of General Hospital of Shenyang Military Area Command, and all subjects provided written informed consent. Twenty-three patients with unruptured IA, including 12 males and 11 females between 41 and 68 (median 58) years of age, and 23 healthy controls, including 10 males and 13 females between 45 and 70 (median 57) years of age, were recruited at General Hospital of Shenyang Military Area Command. All patients and healthy controls
IL-2 significantly improved the proliferation of Treg cells from IA patients
We previously demonstrated that Treg cells from IA patients, upon treatment with external IL-2, presented an upregulation of Tim-3 expression on the surface [18]. It remains unclear whether IL-2 treatment also changed the functional characteristics of Treg cells. Hence, in this study, we first examined the proliferation of Treg cells from IA patients following IL-2 treatment. CD4+CD25− T conventional (Tconv) cells and CD4+CD25+ Treg cells were collected from 23 IA patients, and were stimulated
Discussion
The formation of IA often involves extensive tissue remodeling procedures associated with the destruction of various cellular and structural components. Pathogenic inflammation often develops as a result, and can further propagate aberrant tissue remodeling [10]. The Treg cells and the regulatory immunity are known to mediate peripheral tolerance and tissue repair; however, our previous study demonstrated that Treg cells in IA patients demonstrated multiple impairments, including reduced
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (81471213) and the Natural Science Foundation of Liaoning Province (2015020415).
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