Peri-alloHCT IL-33 administration expands recipient T-regulatory cells that protect mice against acute GVHD.

During allogeneic hematopoietic cell transplantation (alloHCT), nonhematopoietic cell interleukin-33 (IL-33) is augmented and released by recipient conditioning to promote type 1 alloimmunity and lethal acute graft-versus-host disease (GVHD). Yet, IL-33 is highly pleiotropic and exhibits potent immunoregulatory properties in the absence of coincident proinflammatory stimuli. We tested whether peri-alloHCT IL-33 delivery can protect against development of GVHD by augmenting IL-33-associated regulatory mechanisms. IL-33 administration augmented the frequency of regulatory T cells (Tregs) expressing the IL-33 receptor, suppression of tumorigenicity-2 (ST2), which persist following total body irradiation. ST2 expression is not exclusive to Tregs and IL-33 expands innate immune cells with regulatory or reparative properties. However, selective depletion of recipient Foxp3(+) cells concurrent with peri-alloHCT IL-33 administration accelerated acute GVHD lethality. IL-33-expanded Tregs protected recipients from GVHD by controlling macrophage activation and preventing accumulation of effector T cells in GVHD-target tissue. IL-33 stimulation of ST2 on Tregs activates p38 MAPK, which drives expansion of the ST2(+) Treg subset. Associated mechanistic studies revealed that proliferating Tregs exhibit IL-33-independent upregulation of ST2 and the adoptive transfer of st2(+) but not st2(-) Tregs mediated GVHD protection. In total, these data demonstrate the protective capacity of peri-alloHCT administration of IL-33 and IL-33-responsive Tregs in mouse models of acute GVHD. These findings provide strong support that the immunoregulatory relationship between IL-33 and Tregs can be harnessed therapeutically to prevent GVHD after alloHCT for treatment of malignancy or as a means for tolerance induction in solid organ transplantation.

IL-33 is an unconventional Alarmin that stimulates IL-2 secretion by dendritic cells to selectively expand IL-33R/ST2+ regulatory T cells.

IL-33 is a recently characterized IL-1 family member that is proposed to function as an alarmin, or endogenous signal of cellular damage, as well as act as a pleiotropic cytokine. The ability of IL-33 to potentiate both Th1 and Th2 immunity supports its role in pathogen clearance and disease immunopathology. Yet, IL-33 restrains experimental colitis and transplant rejection by expanding regulatory T cells (Treg) via an undefined mechanism. We sought to determine the influence of IL-33 on hematopoietic cells that drives Treg expansion and underlies the therapeutic benefit of IL-33 administration. In this study, we identify a feedback loop in which conventional mouse CD11c(+) dendritic cells (DC) stimulated by IL-33 secrete IL-2 to selectively expand IL-33R(ST2(+))- suppressive CD4(+)Foxp3(+) Treg. Interestingly, this occurs in the absence of classical DC maturation, and DC-derived (innate) IL-2 increases ST2 expression on both DC and interacting Treg. ST2(+) Treg represent an activated subset of Foxp3(+) cells, demonstrated to be ICOS(high)CD44(high) compared with their ST2(-) counterparts. Furthermore, although studies have shown that IL-33-exposed DC promote Th2 responses, we reveal that ST2(+) DC are required for IL-33-mediated in vitro and in vivo Treg expansion. Thus, we have uncovered a relationship between IL-33 and innate IL-2 that promotes the selective expansion of ST2(+) Treg over non-Treg. These findings identify a novel regulatory pathway driven by IL-33 in immune cells that may be harnessed for therapeutic benefit or for robust expansion of Treg in vitro and in vivo.

Correction: Type V Collagen Induced Tolerance Suppresses Collagen Deposition, TGF-ß and Associated Transcripts in Pulmonary Fibrosis.

[This corrects the article DOI: 10.1371/journal.pone.0076451.].

New dog and new tricks: evolving roles for IL-33 in type 2 immunity.

IL-33 is a more recently identified member of the IL-1 cytokine family, expressed in the nucleus of epithelial cells and released into the extracellular space following tissue damage. The impact of IL-33 as a regulator of the adaptive immune response has been studied extensively, with an understood role for IL-33 in the effector functions of CD4(+) Th2 cells. IL-33, however, is now being shown to initiate the Th2-polarizing function of DCs, and stimulate the secretion of the type 2-associated cytokines, IL-4, IL-5, and IL-13, from tissue-resident innate-immune cells, especially ILCs and MCs. IL-33 also initiates and perpetuates local inflammatory responses through the recruitment and activation of type 2- and inflammatory-associated effectors, such as eosinophils, basophils, and neutrophils. As such, IL-33 drives and amplifies type 2-dependent immunity, as well as type 2-dependent tissue destruction and inflammation. It is also becoming apparent that IL-33 supports the reparative capacity of macrophage and ILCs, but these functions may also contribute to chronic fibrotic diseases. Herein, we review new developments in the understanding of IL-33 as it functions in Th2 cells and type 2 immunity. This includes a discussion of our evolving understanding of how IL-33 directly and indirectly promotes type 2 immune responses through action on innate cells in immunity and the pathogenesis of atopic and fibrotic diseases.

Type V collagen induced tolerance suppresses collagen deposition, TGF-ß and associated transcripts in pulmonary fibrosis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by progressive scarring and matrix deposition. Recent reports highlight an autoimmune component in IPF pathogenesis. We have reported anti-col(V) immunity in IPF patients. The objective of our study was to determine the specificity of col(V) expression profile and anti-col(V) immunity relative to col(I) in clinical IPF and the efficacy of nebulized col(V) in pre-clinical IPF models. METHODS: Col(V) and col(I) expression profile was analyzed in normal human and IPF tissues. C57-BL6 mice were intratracheally instilled with bleomycin (0.025 U) followed by col(V) nebulization at pre-/post-fibrotic stage and analyzed for systemic and local responses. RESULTS: Compared to normal lungs, IPF lungs had higher protein and transcript expression of the alpha 1 chain of col(V) and col(I). Systemic anti-col(V) antibody concentrations, but not of anti-col(I), were higher in IPF patients. Nebulized col(V), but not col(I), prevented bleomycin-induced fibrosis, collagen deposition, and myofibroblast differentiation. Col(V) treatment suppressed systemic levels of anti-col(V) antibodies, IL-6 and TNF-α; and local Il-17a transcripts. Compared to controls, nebulized col(V)-induced tolerance abrogated antigen-specific proliferation in mediastinal lymphocytes and production of IL-17A, IL-6, TNF-α and IFN-γ. In a clinically relevant established fibrosis model, nebulized col(V) decreased collagen deposition. mRNA array revealed downregulation of genes specific to fibrosis (Tgf-ß, Il-1ß, Pdgfb), matrix (Acta2, Col1a2, Col3a1, Lox, Itgb1/6, Itga2/3) and members of the TGF-ß superfamily (Tgfbr1/2, Smad2/3, Ltbp1, Serpine1, Nfkb/Sp1/Cebpb). CONCLUSIONS: Anti-col(V) immunity is pathogenic in IPF, and col(V)-induced tolerance abrogates bleomycin-induced fibrogenesis and down regulates TGF- ß-related signaling pathways.

Lamp-2a facilitates MHC class II presentation of cytoplasmic antigens.

Extracellular antigens are internalized and processed before binding MHC class II molecules within endosomal and lysosomal compartments of professional antigen presenting cells (APC) for subsequent presentation to T cells. Yet select cytoplasmic peptides derived from autoantigens also intersect and bind class II molecules via an unknown mechanism. In human B lymphoblasts, inhibition of the peptide transporter associated with antigen processing (TAP) failed to alter class II-restricted cytoplasmic epitope presentation. By contrast, decreased display of cytoplasmic epitopes via class II molecules was observed in cells with diminished expression of the lysosome-associated membrane protein-2 (Lamp-2). Overexpression of Lamp-2 isoform A (Lamp-2a), an established component of chaperone-mediated autophagy, enhanced cytoplasmic autoantigen presentation. Manipulating APC expression of heat shock cognate protein 70 (hsc70), a cofactor for Lamp-2a, also altered cytoplasmic class II peptide presentation. These results demonstrate a novel role for the lysosomal Lamp-2a-hsc70 complex in promoting immunological recognition and antigen presentation.