Synthetic fibronectin peptides interrupt inflammatory cell infiltration in transforming growth factor beta 1 knockout mice.

TGF-β1 plays an important role in the maintenance of immune homeostasis and self-tolerance. To determine the mechanism by which TGF-β1 prevents autoimmunity we have analyzed T cell activation in splenic lymphocytes from TGF-β1-deficient mice. Here we demonstrate that unlike wild-type splenic lymphocytes, those from Tgfb1−/− mice are hyporesponsive to receptor-mediated mitogenic stimulation, as evidenced by diminished proliferation and reduced IL-2 production. However, they have elevated levels of IFN-γ and eventually undergo apoptosis. Receptor-independent stimulation of Tgfb1−/− T cells by PMA plus ionomycin induces IL-2 production and mitogenic response, and it rescues them from anergy. Tgfb1−/− T cells display decreased CD3 expression; increased expression of the activation markers LFA-1, CD69, and CD122; and increased cell size, all of which indicate prior activation. Consistently, mutant CD4+ T cells have elevated intracellular Ca2+ levels. However, upon subsequent stimulation in vitro, increases in Ca2+ levels are less than those in wild-type cells. This is also consistent with the anergic phenotype. Together, these results demonstrate that the ex vivo proliferative hyporesponsiveness of Tgfb1−/− splenic lymphocytes is due to prior in vivo activation of T cells resulting from deregulated intracellular Ca2+ levels.

Section: Discussionsupporting

confidence: 76%

TGF-β1 Regulates Lymphocyte Homeostasis by Preventing Activation and Subsequent Apoptosis of Peripheral Lymphocytes

Bommireddy¹,

Saxena²,

Ormsby³

et al. 2003

“…Although the underlying instigatory mechanism of the inflammatory pathology is not known, the ability to modulate the inflammatory sequelae by blocking recruitment and migration (30,31), activation (8,32), and, as demonstrated here, signal transduction, by targeting either NF-B activation or TLR4 expression, highlights the complexity of the inflammatory phenotype of the TGF-␤1 null mouse. However, in the absence of any identifiable pathologic agent, the initiator of these events remains a mystery.…”

Section: Discussionmentioning

confidence: 99%

Aberrant Toll Receptor Expression and Endotoxin Hypersensitivity in Mice Lacking a Functional TGF-β1 Signaling Pathway

McCartney-Francis

Jin

Wahl

2004

TGF-β1 plays a central role in maintaining normal immune function and deficiency of this potent immunosuppressive molecule is linked to uncontrolled inflammation, cachexia, and multiorgan failure as seen in the TGF-β1 null mouse. Infiltration of inflammatory cells into vital organs of the null mouse is accompanied by increased gene expression of inflammatory cytokines, including TNF-α and IL-1β, as well as inducible NO synthase, each regulated by NF-κB. Treatment with the proteasome inhibitor MG132 to prevent NF-κB activation dramatically reduced NO production and expression of inflammatory cytokines. This inflammatory phenotype with NF-κB activation in the TGF-β1 null mouse, in the absence of any identifiable pathogen, suggested activation of innate immune responses. Because Toll-like receptors (TLR) are essential in the activation of innate immunity, we examined inflamed tissue from TGF-β1 null and wild-type mice for expression of TLR4, the receptor that interacts with bacterial cell wall LPS to initiate an NF-κB-dependent signaling pathway, leading to gene transcription of inflammatory mediators. Increased TLR4 mRNA expression observed in TGF-β1 null mice as well as in mice lacking the TGF-β transcription factor Smad3 was associated with LPS hyperresponsiveness leading to increased expression of inflammatory cytokines and NO and endotoxemia. Furthermore, mice lacking both TGF-β1 and a functional TLR4 were resistant to endotoxin shock. Constitutive and/or environmental activation of TLR4 and downstream elements, in the absence of TGF-β suppression, may impact on innate and adaptive immunity and contribute to massive uncontrolled inflammation.

“…Null mice treated with normal rat IgG experienced the typical wasting syndrome which ensued at ϳ12-14 days of age (data not shown and Ref. 15) and died by 15-19 days. In comparison, mice treated with anti-IFN-␥ maintained a constant weight or increased in weight, and life span was extended by nearly 2-fold to days 29 -32 ( p ϭ 0.004 as compared with IgG-treated null mice) (Fig.…”

Section: Treatment With Anti-ifn-␥ Increases the Life Span Of The Tgfmentioning

confidence: 99%

“…Infiltration of lymphocytes and macrophages, particularly in heart and lungs, is associated with cardiopulmonary failure. Increased MHC Ag, cytokines, adhesion molecules, and autoantibody expression suggest an autoimmune origin of the pathological lesions (12)(13)(14)(15)(16)(17). Recent studies have shown enhanced expression of IFN-␥ RNA before the appearance of inflammatory lesions in TGF-␤1 null mice (13), consistent with disruption of immunoregulatory circuits in the absence of TGF-␤1.…”

Section: Dysregulation Of Ifn-␥ Signaling Pathways In the Absence Of mentioning

confidence: 99%

Dysregulation of IFN-γ Signaling Pathways in the Absence of TGF-β1

McCartney-Francis

Wahl

2002

Deficiency of TGF-β1 is associated with immune dysregulation and autoimmunity as exemplified by the multifocal inflammatory lesions and early demise of the TGF-β1 null mice. Elevated NO metabolites (nitrite and nitrate) in the plasma of these mice suggest a participatory role of NO in the pathogenic inflammatory response. To determine the mechanism for this dysregulation, we examined upstream elements that could contribute to the overexpression of NO, including inducible NO synthase (iNOS) and transcription factors Stat1α and IFN-regulatory factor-1 (IRF-1). The coincident up-regulation of IFN-γ, an iNOS inducer, and iNOS, before the appearance of inflammatory lesions, suggests that failed regulation of the IFN-γ signaling pathway may underlie the immunological disorder in TGF-β1 null mice. In fact, IFN-γ-driven transcription factors IRF-1 and Stat1α, both of which act as transcriptional activators of iNOS, were elevated in the null mice. Treatment of mice with a polyclonal anti-IFN-γ Ab reduced expression and activity not only of transcription factors Stat1α and IRF-1 but also of iNOS. Furthermore, anti-IFN-γ treatment delayed the cachexia normally seen in TGF-β1 null mice and increased their longevity. The global nature of immune dysregulation in TGF-β1 null mice documents TGF-β1 as an essential immunoregulatory molecule.