Frontline: Absence of functional STAT4 activation despite detectable tyrosine phosphorylation induced by murine IFN‐α

Humans and mice have evolved distinct pathways for Th1 cell development. Although IL-12 promotes CD4+ Th1 development in both murine and human T cells, IFN-αβ drives Th1 development only in human cells. This IFN-αβ-dependent pathway is not conserved in the mouse species due in part to a specific mutation within murine Stat2. Restoration of this pathway in murine T cells would provide the opportunity to more closely model specific human disease states that rely on CD4+ T cell responses to IFN-αβ. To this end, the C terminus of murine Stat2, harboring the mutation, was replaced with the corresponding human Stat2 sequence by a knockin targeting strategy within murine embryonic stem cells. Chimeric m/h Stat2 knockin mice were healthy, bred normally, and exhibited a normal lymphoid compartment. Furthermore, the murine/human STAT2 protein was expressed in murine CD4+ T cells and was activated by murine IFN-α signaling. However, the murine/human STAT2 protein was insufficient to restore full IFN-α-driven Th1 development as defined by IFN-γ expression. Furthermore, IL-12, but not IFN-α, promoted acute IFN-γ secretion in collaboration with IL-18 stimulation in both CD4+ and CD8+ T cells. The inability of T cells to commit to Th1 development correlated with the lack of STAT4 phosphorylation in response to IFN-α. This finding suggests that, although the C terminus of human STAT2 is required for STAT4 recruitment and activation by the human type I IFNAR (IFN-αβR), it is not sufficient to restore this process through the murine IFNAR complex.

Section: Discussionsupporting

confidence: 88%

IL-12, but Not IFN-α, Promotes STAT4 Activation and Th1 Development in Murine CD4+ T Cells Expressing a Chimeric Murine/Human Stat2 Gene

Persky

Murphy

Farrar

2005

“…Moreover, we determined that the role of STAT1 in Th1 cell trafficking was specific to Th1 cells as Ag-specific Th2 cells traffic normally in STAT1 Ϫ/Ϫ mice. CD4 ϩ T cells from STAT1 Ϫ/Ϫ mice have been shown to differentiate to a Th1 phenotype and secrete IFN-␥ but to a lesser extent than the WT (33). Therefore, we used an adoptive transfer model to isolate the role of STAT1 in Th1 cell trafficking apart from its role in Th1 cell differentiation.…”

Section: Discussionmentioning

confidence: 99%

STAT1 in Peripheral Tissue Differentially Regulates Homing of Antigen-Specific Th1 and Th2 Cells

Mikhak

Fleming

Medoff

et al. 2006

Th1 and Th2 effector CD4+ T cells orchestrate distinct counterregulatory biological responses. To deliver effective tissue Th1- and Th2-type responses, Th1 and Th2 cell recruitment into tissue must be differentially regulated. We show that tissue-derived STAT1 controls the trafficking of adoptively transferred, Ag-specific, wild-type Th1 cells into the lung. Trafficking of Th1 and Th2 cells is differentially regulated as STAT6, which regulates Th2 cell trafficking, had no effect on the trafficking of Th1 cells and STAT1 deficiency did not alter Th2 cell trafficking. We demonstrate that STAT1 control of Th1 cell trafficking is not mediated through T-bet. STAT1 controls the recruitment of Th1cells through the induction of CXCL9, CXCL10, CXCL11, and CXCL16, whose expression levels in the lung were markedly decreased in STAT1−/− mice. CXCL10 replacement partially restored Th1 cell trafficking in STAT1-deficient mice in vivo, and deficiency in CXCR3, the receptor for CXCL9, CXCL10, and CXCL11, impaired the trafficking of adoptively transferred Th1 cells in wild-type mice. Our work identifies that STAT1 in peripheral tissue regulates the homing of Ag-specific Th1 cells through the induction of a distinct subset of chemokines and establishes that Th1 and Th2 cell trafficking is differentially controlled in vivo by STAT1 and STAT6, respectively.

“…For some time, the actions of type I IFN, such as IFN-␣, were thought to differ between the human and murine system. While IFN-␣ was claimed to drive Th1 development in human T cells (8 -10), type I IFN did not drive Th1 development in mouse T cells (11)(12)(13). Type I IFN were thought to induce STAT4 phosphorylation in human T cells, but not murine Th1 cells (14,15).…”

Section: T He Differentiation Of Naive Cd4mentioning

confidence: 99%

“…Type I IFN were thought to induce STAT4 phosphorylation in human T cells, but not murine Th1 cells (14,15). However, it was recently reported that IFN-␣ can activate STAT4 in murine T cells responding to lymphocytic choriomeningitis virus (LCMV) 4 infection (16) or already differentiated Th1 cells (13), although these studies did not demonstrate the ability of IFN-␣ to induce Th1 differentiation. A potential species-specific STAT4 activation by IFN-␣ was proposed to involve a mutation in the murine STAT2 gene that would diminish STAT4 recruitment (15,17).…”

Section: T He Differentiation Of Naive Cd4mentioning

confidence: 99%

Distinct Characteristics of Murine STAT4 Activation in Response to IL-12 and IFN-α

Berenson

Gavrieli

Farrar

et al. 2006

The role of type I IFN in Th1 development, STAT4 activation, and IFN-γ production in murine T cells has remained unresolved despite extensive examination. Initial studies indicated that IFN-α induced Th1 development and IFN-γ production in human, but not murine, T cells, suggesting species-specific differences in signaling. Later studies suggested that IFN-α also induced Th1 development in mice, similar to IL-12. More recent studies have questioned whether IFN-α actually induces Th1 development even in the human system. In the present study, we compared the capacity of IL-12 and IFN-α to induce Th1 differentiation, STAT4 phosphorylation, and IFN-γ production in murine T cells. First, we show that IFN-α, in contrast to IL-12, cannot induce Th1 development. However, in differentiated Th1 cells, IFN-α can induce transient, but not sustained, STAT4 phosphorylation and, in synergy with IL-18, can induce transient, but not sustained, IFN-γ production in Th1 cells, in contrast to the sustained actions of IL-12. Furthermore, loss of STAT1 increases IFN-α-induced STAT4 phosphorylation, but does not generate levels of STAT4 activation or IFN-γ production achieved by IL-12 or convert transient STAT4 activation into a sustained response. Our findings agree with recent observations in human T cells that IFN-α-induced STAT4 activation is transient and unable to induce Th1 development, and indicate that IFN-α may act similarly in human and murine T cells.