Interleukin-2 (IL-2) Interacts With IL-2 Receptor Beta (IL-2Rβ): Its Potential to Enhance the Proliferation of CD4+ T Lymphocytes in Flounder (Paralichthys olivaceus).

Xiujuan Zhou,Heng Chi,Jing Xing,Xiuzhen Sheng,Wenbin Zhan,Xiaoqian Tang

doi:10.3389/fimmu.2020.531785

Abstract

Interleukin-2 (IL-2) is an important immunomodulatory cytokine that primarily promotes the activation, proliferation, and differentiation of CD4+ T helper subsets and CD4+ T regulatory cells. In our previous studies, IL-2 and IL-2 receptor beta (IL-2Rβ) genes of flounder (Paralichthys olivaceus) were cloned, and IL-2Rβ molecules expressed on both B and T lymphocytes were identified. In the present study, the interaction of flounder IL-2 (fIL-2) with the IL-2 receptor beta (fIL-2Rβ) was investigated. The proportion of CD4+ T lymphocytes and IL-2Rβ+ cells were detected both in vivo and in vitro. Firstly, the binding of recombinant flounder IL-2 protein (rfIL-2) and rfIL-2Rβ was verified by pull-down assay and enzyme-linked immunosorbent assay. Indirect immunofluorescence assay showed that rfIL-2 enhanced the proliferation of CD4+ and IL-2Rβ+ cells in the gill and spleen. Furthermore, CD4-1+, CD4-2+ T lymphocytes and IL-2Rβ+ cells were significantly upregulated in cultured peripheral blood lymphocytes (PBLs) with addition of rfIL-2, as shown by Flow cytometry. The related genes were examined by Q-PCR in cultured PBLs with added rfIL-2. The results showed that the IL-2–IL-2R interaction induced upregulated expression of T lymphocyte surface makers, Th1-related cytokines or transcription factors, and critical genes of the IL-2 signaling pathway. In addition, these IL-2–elicited biological functions and immune responses were downregulated by blocked with anti–rfIL-2Rβ and anti–rfIL-2 Abs, showing that IL-2Rβ plays an indispensable role in IL-2 elicited biological function. Our results demonstrated that the interaction between IL-2 and IL-2Rβ showed its potential to enhance the proliferation of CD4+ T lymphocytes in flounder. As found in mammals, a Th1-mediated mechanism regulated by this interaction exists in teleost.

Highlights

In mammals, Interleukin-2 (IL-2), a four α-helical bundle cytokine with a molecular weight of 15kDa, is a T cell growth factor that is mainly produced by activated T cells [1]
SDSPAGE revealed that His-recombinant flounder IL-2 protein (rfIL-2) and GST-rfIL-2Rβ had molecular masses of 20.8 and 49 kDa, respectively, which were consistent with their theoretical molecular masses
The results revealed that GST-rfIL-2Rβ could efficiently binding with His-rfIL-2

Summary

Introduction

Interleukin-2 (IL-2), a four α-helical bundle cytokine with a molecular weight of 15kDa, is a T cell growth factor that is mainly produced by activated T cells [1]. IL-2 is a critical Th1-type cytokine that plays an important role in immune regulation, wherein it primarily promotes the activation, proliferation, and differentiation of T cells, B cells, and NK cells [2, 3]. Activated T cells, including CD4+ and CD8+ T cells, secrete a high amount of IL-2 to induce autocrine effects as well as paracrine stimulation of their neighboring IL-2 receptor (IL-2R)-expressing cells [4, 5]. IL-2 binds to the receptor complex to elicit intracellular signaling events that lead to cell proliferation [8, 9]. IL-2 binding to IL-2R to form a ligandreceptor complex triggers the phosphorylation of transcription factors, leading to induction of gene expression. The resulting signal transduction occurs via three major pathways, JAK-STAT, PI3K-AKT, and MAPK [10]

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Conclusion