An Alternative Pathway of Imiquimod-Induced Psoriasis-Like Skin Inflammation in the Absence of Interleukin-17 Receptor A Signaling

Topical application of imiquimod (IMQ) on the skin of mice induces inflammation with common features found in psoriatic skin. Recently, it was postulated that IL-17 has an important role both in psoriasis and in the IMQ model. To further investigate the impact of IL-17RA signaling in psoriasis, we generated IL-17 receptor A (IL-17RA)–deficient mice (IL-17RAdel) and challenged these mice with IMQ. Interestingly, the disease was only partially reduced and delayed but not abolished when compared with controls. In the absence of IL-17RA, we found persisting signs of inflammation such as neutrophil and macrophage infiltration within the skin. Surprisingly, already in the naive state, the skin of IL-17RAdel mice contained significantly elevated numbers of Th17- and IL-17-producing γδ T cells, assuming that IL-17RA signaling regulates the population size of Th17 and γδ T cells. Upon IMQ treatment of IL-17RAdel mice, these cells secreted elevated amounts of tumor necrosis factor-α, IL-6, and IL-22, accompanied by increased levels of the chemokine CXCL2, suggesting an alternative pathway of neutrophil and macrophage skin infiltration. Hence, our findings have major implications in the potential long-term treatment of psoriasis by IL-17-targeting drugs

ACE Inhibition Modulates Myeloid Hematopoiesis after Acute Myocardial Infarction and Reduces Cardiac and Vascular Inflammation in Ischemic Heart Failure

Aims: Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a cornerstone of drug therapy after myocardial infarction (MI) and improve left ventricular function and survival. We aimed to elucidate the impact of early treatment with the ACE inhibitor ramipril on the hematopoietic response after MI, as well as on the chronic systemic and vascular inflammation. Methods and Results: In a mouse model of MI, induced by permanent ligation of the left anterior descending artery, immediate initiation of treatment with ramipril (10 mg/k/d via drinking water) reduced cardiac inflammation and the number of circulating inflammatory monocytes, whereas left ventricular function was not altered significantly, respectively. This effect was accompanied by enhanced retention of hematopoietic stem cells, Lin−Sca1−c-Kit+CD34+CD16/32+ granulocyte–macrophage progenitors (GMP) and Lin−Sca1−c-Kit+CD150−CD48− multipotent progenitors (MPP) in the bone marrow, with an upregulation of the niche factors Angiopoetin 1 and Kitl at 7 d post MI. Long-term ACE inhibition for 28 d limited vascular inflammation, particularly the infiltration of Ly6Chigh monocytes/macrophages, and reduced superoxide formation, resulting in improved endothelial function in mice with ischemic heart failure. Conclusion: ACE inhibition modulates the myeloid inflammatory response after MI due to the retention of myeloid precursor cells in their bone marrow reservoir. This results in a reduction in cardiac and vascular inflammation with improvement in survival after MI

No differences of <i>Il6ra^Δmyel</i> mice in myelomonocytic cells and T cells compared to <i>wt</i> in IMQ-induced psoriasis.

<p>(A) Flow cytometric analysis of CD11b⁺ cells of the indicated organs. Cells are pre-gated on living CD90.2^-/B220^- cells. (B) Total cell numbers of CD11b⁺ cells of the indicated organs. Bar graphs are shown with mean and SEM. Significance was calculated using Kruskal-Wallis test. (C) Flow cytometric analysis of Ly6C⁺ and Ly6G⁺ cells of the indicated organs. Cells are pre-gated on living CD90.2^-/B220^- and CD11b⁺ cells. (D) Total cell numbers of Ly6G⁺ cells, pro-inflammatory monocytes (Ly6G^-Ly6C^hi) and resident monocytes (Ly6G^-Ly6C^int). Bar graphs of the indicated organs are shown with mean and SEM. Significances of the spleen were calculated using Kruskal-Wallis test (IMQ groups n = 6, sham groups n = 3). Significances of the ears were calculated with Student’s t-Test (IMQ groups n = 6, sham groups n = 1). (E) Flow cytometric analysis of IL-17A producing γδ T cells of the indicated organs. Cells are pre-gated on living CD45.2⁺/CD3⁺ cells. (F) Total cell numbers of γδ TCR⁺ and IL-17A⁺ γδ TCR⁺. Data are shown as bar graphs with mean and SEM. Significance was calculated using Kruskal-Wallis test.</p

<i>Il6ra</i>^{<i>Δmyel</i>} mice show no differences in myelomonocytic cell compartments and T cells compared to <i>wt</i>.

<p>(A) Flow cytometric analysis of CD11b⁺ cells of the indicated organs. Cells are pre-gated on living CD90.2^-/CD19^- cells (n = 5). (B) Percentages and total cell numbers of CD11b⁺ cells of the indicated organs. Bar graphs are shown with mean and SEM. Significance was calculated using Mann Whitney test (n = 5). (C) Flow cytometric analysis of Gr-1⁺ and F4/80⁺ cells of the indicated organs. Cells are pre-gated on living CD90.2^-/CD19^- and CD11b⁺ cells (n = 5). (D) Total cell numbers of neutrophils (Gr-1^hi F4/80^-), monocytes (Gr-1^int F4/80⁺) and macrophages (Gr-1^- F4/80⁺). Data are shown as bar graphs with mean and SEM. Significance was calculated using Mann Whitney test (n = 5). (E) Flow cytometric analysis of IL-17A producing γδ T cells of indicated organs. Cells are pre-gated on living CD45.2⁺/CD3⁺ cells (n = 5). (F) Total cell numbers of γδ TCR⁺ and IL-17A⁺ γδ TCR⁺. Data are shown as bar graphs with mean and SEM. Significance was calculated using Mann Whitney test (n = 5).</p

<i>Il6ra</i>^{<i>Δmyel</i>} mice show no effect in clinical scores and histology in IMQ-induced psoriasis compared to <i>wt</i> mice.

<p>(A) Weight, ear/back skin thickness and erythema/scaling was scored daily on a scale from 0 to 4 with a modified PASI from human. IMQ treated groups with n = 6, sham treated group n = 3. (B) Back skin of <i>Il6ra</i>^{<i>Δmyel</i>} and <i>wt</i> mice treated with sham (show one representative) or IMQ (n = 5) was stained by fluorescence-Immunohistochemistry for myeloperoxidase (MPO)⁺. (C) Back skin of <i>Il6ra</i>^{<i>Δmyel</i>} and <i>wt</i> mice treated with sham (show one representative) or IMQ (n = 5) was stained by fluorescence-Immunohistochemistry for F4/80⁺. (magnifications are given from representative stainings), white scale bars = 200μm.</p

Functionality of <i>Il6ra</i>^{<i>Δmyel</i>} mice.

<p>(A) Flow cytometric analysis of IL-6Rα expression of different organs. CD4⁺ cells are pre-gated on living CD90.2⁺ cells. Neutrophils (Gr-1^hi F4/80^-), monocytes (Gr-1^int F4/80⁺) and macrophages (Gr-1^- F4/80⁺) are pre-gated on living CD90.2^-/B220^- and CD11b⁺ cells. Gray histograms represent IgG2b isotype control for the IL-6R staining. Numbers in upper right corner represent the mean Mean Fluorescent Intensity (MFI) values of Il6ra^Δmyel or <i>wt</i> cells. Shown are representative histograms (n = 7 or 8 (3 independent experiments). (B) MFI of IL-6Rα expression pre-gated on CD4⁺ cells, neutrophils (Gr-1^hi F4/80^-), monocytes (Gr-1^int F4/80⁺) or macrophages (Gr-1^- F4/80⁺). Data are shown as bar graphs with mean and SEM. *p ≤ 0,05 Significance was calculated using Mann Whitney test. (C) Quantitative RT-PCR from CD11b⁺ MACS purified bone marrow cells for the IL-6Rα gene in <i>wt</i> and <i>Il6ra</i>^{<i>Δmyel</i>} mice. Expression levels are shown relative to the housekeeping gene HPRT (n = 5). Data are shown as bar graphs with mean and SEM. * p ≤ 0,05 Significance was calculated using Mann Whitney test. (D) Serum concentrations of sIL-6Rα examined by ELISA in <i>wt</i> (n = 6) and <i>Il6ra</i>^{<i>Δmyel</i>} (n = 10) mice at the age of 5 weeks to 5 months. Data are shown as bar graphs with mean and SEM. *** p ≤ 0,001 Significance was calculated using Mann Whitney test.</p

Cutting Edge: IL-6-Driven Immune Dysregulation Is Strictly Dependent on IL-6R alpha-Chain Expression

IL-6 binds to the IL-6R alpha-chain (IL-6R alpha) and signals via the signal transducer gp130. Recently, IL-6 was found to also bind to the cell surface glycoprotein CD5, which would then engage gp130 in the absence of IL-6R alpha. However, the biological relevance of this alternative pathway is under debate. In this study, we developed a mouse model, in which murine IL-6 is overexpressed in a CD11c-Cre-dependent manner. Transgenic mice developed a lethal immune dysregulation syndrome with increased numbers of Ly-6G(+) neutrophils and Ly-6C(hi) monocytes/macrophages. IL-6 overexpression promoted activation of CD4(+) T cells while suppressing CD5(+) B-1a cell development. However, additional ablation of IL-6R alpha protected IL-6-overexpressing mice from IL-6-triggered inflammation and fully phenocopied IL-6R alpha-deficient mice without IL-6 overexpression. Mechanistically, IL-6R alpha deficiency completely prevented downstream activation of STAT3 in response to IL-6. Altogether, our data clarify that IL-6R alpha is the only biologically relevant receptor for IL-6 in mice