Inflammation Enhances IL-2 Driven Differentiation of Cytolytic CD4 T Cells

Aspen M Workman,Alexander J Vogel,Ashley K Jacobs,Deborah M Brown,Shirley Condon,Paul G Thomas

doi:10.1371/journal.pone.0089010

Abstract

Cytolytic CD4 T cells (CD4 CTL) have been identified in vivo in response to viral infections; however, the factors necessary for driving the cytolytic phenotype have not been fully elucidated. Our previously published work suggests IL-2 may be the master regulator of perforin-mediated cytotoxicity in CD4 effectors. To further dissect the role of IL-2 in CD4 CTL generation, T cell receptor transgenic mice deficient in the ability to produce IL-2 or the high affinity IL-2 receptor (IL-2Rα, CD25) were used. Increasing concentrations of IL-2 were necessary to drive perforin (Prf) expression and maximal cytotoxicity. Granzyme B (GrB) expression and killing correlated with STAT5 activation and CD25 expression in vitro, suggesting that signaling through the high affinity IL-2R is critical for full cytotoxicity. IL-2 signaling was also necessary in vivo for inducing the Th1 phenotype and IFN-γ expression in CD4 T cells during influenza A (IAV) infection. In addition, GrB expression, as measured by mean fluorescent intensity, was decreased in CD25 deficient cells; however, the frequency of CD4 cells expressing GrB was unchanged. Similarly, analysis of cytolytic markers such as CD107a/b and Eomesodermin indicate high IL-2Rα expression is not necessary to drive the CD4 CTL phenotype during IAV infection. Thus, inflammatory signals induced by viral infection may overcome the need for strong IL-2 signals in driving cytotoxicity in CD4 cells.

Highlights

CD4 T cells play a central role in immune responses to infection as well as acting in a regulatory role for maintaining homeostasis
We further demonstrated that exogenous IL-2 was necessary and sufficient to induce a cytolytic phenotype in CD4 T cells stimulated in vitro with peptide pulsed antigen presenting cells (APC) [23]
Our earlier work demonstrated that exogenous IL-2 and peptide pulsed antigen presenting cells (APCs) were the minimal requirements necessary to induce perforin (Prf)-mediated cytotoxicity in CD4 T cells [23]

Summary

Introduction

CD4 T cells play a central role in immune responses to infection as well as acting in a regulatory role for maintaining homeostasis. In vivo generated effectors used perforin exclusively to mediate cytotoxicity after activation by influenza viral infection [13], ectromelia virus [16] and in anti-tumor vaccination models [24]. We further demonstrated that exogenous IL-2 was necessary and sufficient to induce a cytolytic phenotype in CD4 T cells stimulated in vitro with peptide pulsed antigen presenting cells (APC) [23]. These studies did not address the contribution of endogenous IL-2 produced by CD4 effectors, or the role of IL-2 signaling in driving CD4 CTL differentiation in vivo. This information will be important when designing vaccine strategies against emerging viral infections and for influenza viruses with pandemic potential

Results

Discussion

Materials and Methods