Induction and maintenance of IL-4 expression are regulated differently by the 3' enhancer in CD4 T cells

Eosinophils Protect Mice From Angiotensin-II Perfusion-Induced Abdominal Aortic Aneurysm

RATIONALE

Blood eosinophil count and ECP (eosinophil cationic protein) associate with human cardiovascular diseases. Yet, whether eosinophils play a role in cardiovascular disease remains untested. The current study detected eosinophil accumulation in human and murine abdominal aortic aneurysm (AAA) lesions, suggesting eosinophil participation in this aortic disease.

OBJECTIVE

To test whether and how eosinophils affect AAA growth.

METHODS AND RESULTS

Population-based randomized clinically controlled screening trials revealed higher blood eosinophil count in 579 male patients with AAA than in 5063 non-AAA control (0.236±0.182 versus 0.211±0.154, 109/L, P<0.001). Univariate (odds ratio, 1.381, P<0.001) and multivariate (odds ratio, 1.237, P=0.031) logistic regression analyses indicated that increased blood eosinophil count in patients with AAA served as an independent risk factor of human AAA. Immunostaining and immunoblot analyses detected eosinophil accumulation and eosinophil cationic protein expression in human and murine AAA lesions. Results showed that eosinophil deficiency exacerbated AAA growth with increased lesion inflammatory cell contents, matrix-degrading protease activity, angiogenesis, cell proliferation and apoptosis, and smooth muscle cell loss using angiotensin-II perfusion-induced AAA in Apoe-/- and eosinophil-deficient Apoe-/-ΔdblGATA mice. Eosinophil deficiency increased lesion chemokine expression, muted lesion expression of IL (interleukin) 4 and eosinophil-associated-ribonuclease-1 (mEar1 [mouse EOS-associated-ribonuclease-1], human ECP homolog), and slanted M1 macrophage polarization. In cultured macrophages and monocytes, eosinophil-derived IL4 and mEar1 polarized M2 macrophages, suppressed CD11b+Ly6Chi monocytes, and increased CD11b+Ly6Clo monocytes. mEar1 treatment or adoptive transfer of eosinophil from wild-type and Il13-/- mice, but not eosinophil from Il4-/- mice, blocked AAA growth in Apoe-/-ΔdblGATA mice. Immunofluorescent staining and immunoblot analyses demonstrated a role for eosinophil IL4 and mEar1 in blocking NF-κB (nuclear factor-κB) activation in macrophages, smooth muscle cells, and endothelial cells.

CONCLUSIONS

Eosinophils play a protective role in AAA by releasing IL4 and cationic proteins such as mEar1 to regulate macrophage and monocyte polarization and to block NF-κB activation in aortic inflammatory and vascular cells.

IL-17A treatment influences murine susceptibility to experimental Riemerella anatipestifer infection

Riemerella anatipestifer causes infectious disease and considerable economic loss in the duck industry worldwide. Our previous studies demonstrated an association between proinflammatory cytokine interleukin (IL)-17A and R. anatipestifer infection. Here, we provide evidence for IL-17A involvement in R. anatipestifer infection using a mouse model. Mice showed higher resistance to R. anatipestifer infection than ducks, with median lethal doses (LD₅₀) of 3.5 × 10¹⁰ and 5 × 10⁷ colony-forming units (CFU), respectively. Twenty-four hours after infection, mice with a sub-lethal dose (3.5 × 10⁹ CFU) exhibited levels of IL-17A and IL-23 expression similar to uninfected mice. Thus, we hypothesized that exogenous IL-17A or IL-23 administration affects susceptibility of mice to R. anatipestifer. Mice pretreated with IL-17A or IL-23 prior to sub-lethal dose infection of R. anatipestifer exhibited increased bacterial burden and spleen weights compared to untreated infected mice, confirming the involvement of IL-17A in susceptibility to R. anatipestifer infection in vivo.

SjHSP60 induces CD4+ CD25+ Foxp3+ Tregs via TLR4-Mal-drived production of TGF-β in macrophages

CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells (Tregs) play a pivotal role in limiting immunopathological damage to host organs after schistosome infection. Transforming growth factor-β (TGF-β) is an essential factor for the periphery conversion of CD4⁺ CD25^- T cells into CD4⁺ CD25⁺ Foxp3⁺ Tregs by inducing the key transcription factor Foxp3. Antigen presenting cells (APCs), which highly express TGF-β, are involved in parasite antigen-induced Treg conversion in peripheral. However, the mechanisms underlying high TGF-β induction in APCs by parasite antigens remain to be clarified during schistosome infection. Here, we demonstrated that Schistosoma japonicum stress protein, heat shock protein 60 (SjHSP60), promoted TGF-β production in macrophages (Mφ). Furthermore, we showed that activation of TLR4-Mal (MyD88 adaptor-like protein) signaling by SjHSP60 is necessary for induction of TGF-β expression in Mφ, which subsequently promoted Treg induction. Our results not only demonstrate a novel mechanism of TGF-β production in Mφ for inducing Tregs in mice with schistosomiasis, but also allude to the possibility of targeting parasite stress protein for potential therapeutics.

Allergic TH2 Response Governed by B-Cell Lymphoma 6 Function in Naturally Occurring Memory Phenotype CD4+ T Cells

Transcriptional repressor B-cell lymphoma 6 (Bcl6) appears to regulate T_H2 immune responses in allergies, but its precise role is unclear. We previously reported that Bcl6 suppressed IL-4 production in naïve CD4⁺ T cell-derived memory T_H2 cells. To investigate Bcl6 function in allergic responses in naturally occurring memory phenotype CD4⁺ T (MPT) cells and their derived T_H2 (MPT_H2) cells, Bcl6-manipulated mice, highly conserved intron enhancer (hcIE)-deficient mice, and reporter mice for conserved noncoding sequence 2 (CNS2) 3′ distal enhancer region were used to elucidate Bcl6 function in MPT cells. The molecular mechanisms of Bcl6-mediated T_H2 cytokine gene regulation were elucidated using cellular and molecular approaches. Bcl6 function in MPT cells was determined using adoptive transfer to naïve mice, which were assessed for allergic airway inflammation. Bcl6 suppressed IL-4 production in MPT and MPT_H2 cells by suppressing CNS2 enhancer activity. Bcl6 downregulated Il4 expression in MPT_H2 cells, but not MPT cells, by suppressing hcIE activity. The inhibitory functions of Bcl6 in MPT and MPT_H2 cells attenuated allergic responses. Bcl6 is a critical regulator of IL-4 production by MPT and MPT_H2 cells in T_H2 immune responses related to the pathogenesis of allergies.

Modular transcriptional repertoire and MicroRNA target analyses characterize genomic dysregulation in the thymus of Down syndrome infants

Trisomy 21-driven transcriptional alterations in human thymus were characterized through gene coexpression network (GCN) and miRNA-target analyses. We used whole thymic tissue--obtained at heart surgery from Down syndrome (DS) and karyotipically normal subjects (CT)--and a network-based approach for GCN analysis that allows the identification of modular transcriptional repertoires (communities) and the interactions between all the system's constituents through community detection. Changes in the degree of connections observed for hierarchically important hubs/genes in CT and DS networks corresponded to community changes. Distinct communities of highly interconnected genes were topologically identified in these networks. The role of miRNAs in modulating the expression of highly connected genes in CT and DS was revealed through miRNA-target analysis. Trisomy 21 gene dysregulation in thymus may be depicted as the breakdown and altered reorganization of transcriptional modules. Leading networks acting in normal or disease states were identified. CT networks would depict the "canonical" way of thymus functioning. Conversely, DS networks represent a "non-canonical" way, i.e., thymic tissue adaptation under trisomy 21 genomic dysregulation. This adaptation is probably driven by epigenetic mechanisms acting at chromatin level and through the miRNA control of transcriptional programs involving the networks' high-hierarchy genes.

A transgenic TCR directs the development of IL-4+ and PLZF+ innate CD4 T cells

MHC class II-expressing thymocytes can efficiently mediate positive selection of CD4 T cells in mice. Thymocyte-selected CD4 (T-CD4) T cells have an innate-like phenotype similar to invariant NKT cells. To investigate the development and function of T-CD4 T cells in-depth, we cloned TCR genes from T-CD4 T cells and generated transgenic mice. Remarkably, positive selection of T-CD4 TCR transgenic (T3) thymocytes occurred more efficiently when MHC class II was expressed by thymocytes than by thymic epithelial cells. Similar to polyclonal T-CD4 T cells and also invariant NKT cells, T3 CD4 T cell development is controlled by signaling lymphocyte activation molecule/signaling lymphocyte activation molecule-associated protein signaling, and the cells expressed both IL-4 and promyelocytic leukemia zinc finger (PLZF). Surprisingly, the selected T3 CD4 T cells were heterogeneous in that only half expressed IL-4 and only half expressed PLZF. IL-4- and PLZF-expressing cells were first found at the double-positive cell stage. Thus, the expression of IL-4 and PLZF seems to be determined by an unidentified event that occurs postselection and is not solely dependent on TCR specificity or the selection process, per se. Taken together, our data show for the first time, to our knowledge, that the TCR specificity regulates but does not determine the development of innate CD4 T cells by thymocytes.

The 3' enhancer CNS2 is a critical regulator of interleukin-4-mediated humoral immunity in follicular helper T cells

A main role for interleukin-4 (IL-4) is in humoral immunity, and follicular helper CD4(+) T (Tfh) cells may be an intrinsic IL-4 source. Here we demonstrate that conserved noncoding sequence 2 (CNS2) is an essential enhancer element for IL-4 expression in Tfh cells but not in Th2 cells. Mice with a CNS2 deletion had a reduction in IgG1 and IgE production and in IL-4 expression in Tfh cells. Tracking of CNS2 activity via a GFP reporter mouse demonstrated that CNS2-active cells expressed several markers of Tfh cells: CXCR5, PD-1, and ICOS; the transcriptional master regulator Bcl6; and the cytokines IL-21 and IL-4. These CNS2-active cells were mainly localized in B cell follicles and germinal centers. The GFP(+) Tfh cells were derived from GFP(-) naive T cells after in vivo systemic immunization. These results indicate that CNS2 is an essential enhancer element required for IL-4 expression in Tfh cells controlling humoral immunity.

Interleukin-4 production by follicular helper T cells requires the conserved Il4 enhancer hypersensitivity site V

Follicular helper T cells (Tfh cells) are the major producers of interleukin-4 (IL-4) in secondary lymphoid organs where humoral immune responses develop. Il4 regulation in Tfh cells appears distinct from the classical T helper 2 (Th2) cell pathway, but the underlying molecular mechanisms remain largely unknown. We found that hypersensitivity site V (HS V; also known as CNS2), a 3' enhancer in the Il4 locus, is essential for IL-4 production by Tfh cells. Mice lacking HS V display marked defects in type 2 humoral immune responses, as evidenced by abrogated IgE and sharply reduced IgG1 production in vivo. In contrast, effector Th2 cells that are involved in tissue responses were far less dependent on HS V. HS V facilitated removal of repressive chromatin marks during Th2 and Tfh cell differentiation and increased accessibility of the Il4 promoter. Thus, Tfh and Th2 cells utilize distinct but overlapping molecular mechanisms to regulate Il4, a finding with important implications for understanding the molecular basis of allergic diseases.

Innate-like CD4 T cells selected by thymocytes suppress adaptive immune responses against bacterial infections

We have reported a new innate-like CD4 T cell population that expresses cell surface makers of effector/memory cells and produce Th1 and Th2 cytokines immediately upon activation. Unlike conventional CD4 T cells that are selected by thymic epithelial cells, these CD4 T cells, named T-CD4 T cells, are selected by MHC class II expressing thymocytes. Previously, we showed that the presence of T-CD4 T cells protected mice from airway inflammation suggesting an immune regulatory role of T-CD4 T cells. To further understand the function of T-CD4 T cells, we investigated immune responses mediated by T-CD4 T cells during bacterial infection because the generation of antigen specific CD4 T cells contributes to clearance of infection and for the development of immune memory. The current study shows a suppressive effect of T-CD4 T cells on both CD8 and CD4 T cell-mediated immune responses during Listeria and Helicobacter infections. In the mouse model of Listeria monocytogenes infection, T-CD4 T cells resulted in decreasedfrequency of Listeria-specific CD8 T cells and the killing activity of them. Furthermore, mice with T-CD4 T cells developed poor immune memory, demonstrated by reduced expansion of antigen-specific T cells and high bacterial burden upon re-infection. Similarly, the presence of T-CD4 T cells suppressed the generation of antigen-specific CD4 T cells in Helicobacter pylori infected mice. Thus, our studies reveal a novel function of T-CD4 T cells in suppressing anti-bacterial immunity.