Kirsten M. Hooper

IL-1R1 Signaling Facilitates Munro’s Microabscess Formation in Psoriasiform Imiquimod-Induced Skin Inflammation

Munro’s microabscesses contain polymorphonuclear leukocytes and form specifically in the epidermis of psoriasis patients. The mechanism whereby the neutrophils are recruited into the epidermis is poorly understood. Using a combination of human and mouse primary keratinocyte cell cultures and the imiquimod-induced psoriasis-like mouse model of skin inflammation we explored the role of interleukin-1 (IL-1) signaling in microabscess formation. In vitro imiquimod stimulated production of IL-1α and neutrophil recruiting chemokines. Imiquimod activated chemokine expression was dependent upon adenosine signaling and independent of IL-1α and IL-1 receptor type 1 (IL-1R1); nevertheless, IL-1α could enhance chemokine expression initiated by imiquimod. Topical application of imiquimod in vivo led to epidermal microabscess formation, acanthosis and increased IL-1α and chemokine expression in the skin of wild type mice. However, in IL-1R1 deficient mice these responses were either absent or dramatically reduced. These results demonstrate that IL-1α and IL-1R1 signaling is essential for microabscess formation, neutrophil recruiting chemokine expression and acanthosis in psoriasis-like skin inflammation induced by imiquimod.

The neuropeptide vasoactive intestinal peptide: direct effects on immune cells and involvement in inflammatory and autoimmune diseases.

Neuropeptides represent an important category of endogenous contributors to the establishment and maintenance of immune deviation in the immune‐privileged organs such as the CNS and in the control of acute inflammation in the peripheral immune organs. Vasoactive intestinal peptide (VIP) is a major immunoregulatory neuropeptide widely distributed in the central and peripheral nervous system. In addition to neurones, VIP is synthesized by immune cells which also express VIP receptors. Here, we review the current information on VIP production and VIP‐receptor‐mediated effects in the immune system, the role of endogenous and exogenous VIP in inflammatory and autoimmune disorders and the present and future VIP therapeutic approaches.

The natural dual cyclooxygenase and 5-lipoxygenase inhibitor flavocoxid is protective in EAE through effects on Th1/Th17 differentiation and macrophage/microglia activation.

Prostaglandins and leukotrienes, bioactive mediators generated by cyclooxygenases (COX) and 5-lipoxygenase (5-LO) from arachidonic acid, play an essential role in neuroinflammation. High levels of LTB4 and PGE2 and increased expression of COX and 5-LO, as well as high expression of PGE2 receptors were reported in multiple sclerosis (MS) patients and in experimental autoimmune encephalomyelitis (EAE). Prostaglandins and leukotrienes have an interdependent and compensatory role in EAE, which led to the concept of therapy using dual COX/5-LO inhibitors. The plant derived flavocoxid, a dual COX/5-LO inhibitor with anti-inflammatory and antioxidant properties, manufactured as a prescription pharmaconutrient, was reported to be neuroprotective in models of transient ischemic stroke and brain injury. The present study is the first report on prophylactic and therapeutic effects of flavocoxid in EAE. The beneficial effects correlate with reduced expression of proinflammatory cytokines and of COX2 and 5-LO in spinal cords and spleens of EAE mice. The protective mechanisms include: 1. reduction in expression of MHCII/costimulatory molecules and production of proinflammatory cytokines; 2. promotion of the M2 phenotype including IL-10 expression and release by macrophages and microglia; 3. inhibition of Th1 and Th17 differentiation through direct effects on T cells. The direct inhibitory effect on Th1/Th17 differentiation, and promoting the development of M2 macrophages and microglia, represent novel mechanisms for the flavocoxid anti-inflammatory activity. As a dual COX/5-LO inhibitor with antioxidant properties, flavocoxid might be useful as a potential therapeutic medical food agent in MS patients.

Differential effects of IFN-β on IL-12, IL-23, and IL-10 expression in TLR-stimulated dendritic cells

MS is an autoimmune disease characterized by immune cell infiltration in the CNS, leading to cumulative disability. IFN‐β, used clinically in RR‐MS reduces lesion formation and rates of relapse. Although the molecular mechanisms are not entirely elucidated, myeloid cells appear to be a major target for the therapeutic effects of IFN‐β. DCs have a critical role in experimental models of MS through their effect on encephalitogenic Th1/Th17 cell differentiation and expansion. Here we focused on the effects of IFN‐β on DC expression of cytokines involved in the control of Th1/Th17 differentiation and expansion. Administration of IFN‐β to mice immunized with MOG35–55 inhibited IL‐12 and IL‐23 expression in splenic DC and reduced in vivo differentiation of Th1/Th17 cells. IFN‐β affected cytokine expression in TLR‐stimulated DC in a similar manner in vitro, inhibiting IL‐12 and IL‐23 and stimulating IL‐10 at both mRNA and protein levels, by signaling through IFNAR. We investigated the role of the signaling molecules STAT1/STAT2, IRF‐1 and IRF‐7, and of the PI3K→GSK3 pathway. IFN‐β inhibition of the IL‐12 subunits p40 and p35 was mediated through STAT1/STAT2, whereas inhibition of IL‐23 was STAT1 dependent, and the stimulatory effect on IL‐10 expression was mediated through STAT2. IFN‐β induces IRF‐7 and, to a lesser degree, IRF‐1. However, neither IRF mediated the effects of IFN‐β on IL‐12, IL‐23, or IL‐10. We found that the PI3K pathway mediated IL‐12 inhibition but did not interfere with the inhibition of IL‐23 or stimulation of IL‐10.

Prostaglandin E2 inhibits Tr1 cell differentiation through suppression of c-Maf

Prostaglandin E2 (PGE2), a major lipid mediator abundant at inflammatory sites, acts as a proinflammatory agent in models of inflammatory/autoimmune diseases by promoting CD4 Th1/Th17 differentiation. Regulatory T cells, including the IL-10 producing Tr1 cells counterbalance the proinflammatory activity of effector Th1/Th17 cells. Tr1 cell differentiation and function are induced by IL-27, and depend primarily on sustained expression of c-Maf in addition to AhR and Blimp-1. In agreement with the in vivo proinflammatory role of PGE2, here we report for the first time that PGE2 inhibits IL-27-induced differentiation and IL-10 production of murine CD4+CD49b+LAG-3+Foxp3- Tr1 cells. The inhibitory effect of PGE2 was mediated through EP4 receptors and induction of cAMP, leading to a significant reduction in c-Maf expression. Although PGE2 reduced IL-21 production in differentiating Tr1 cells, its inhibitory effect on Tr1 differentiation and c-Maf expression also occurred independent of IL-21 signaling. PGE2 did not affect STAT1/3 activation, AhR expression and only marginally reduced Egr-2/Blimp-1 expression. The effect of PGE2 on CD4+CD49b+LAG-3+ Tr1 differentiation was not associated with either induction of Foxp3 or IL-17 production, suggesting a lack of transdifferentiation into Foxp3+ Treg or effector Th17 cells. We recently reported that PGE2 inhibits the expression and production of IL-27 from activated conventional dendritic cells (cDC) in vivo and in vitro. The present study indicates that PGE2 also reduces murine Tr1 differentiation and function directly by acting on IL-27-differentiating Tr1 cells. Together, the ability of PGE2 to inhibit IL-27 production by cDC, and the direct inhibitory effect on Tr1 differentiation mediated through reduction in c-Maf expression, represent a new mechanistic perspective for the proinflammatory activity of PGE2.

Immunomodulation by Vasoactive Intestinal Polypeptide (VIP)

Vasoactive intestinal peptide (VIP) is one of the major neuropeptides expressed and produced by the enteric nervous system. VIP release in the proximity of GI resident immune cells facilitates its immunoregulatory functions, including effects on macrophages, dendritic cells, and T lymphocytes. Here we discuss the functions of VIP as a modulator and possible therapeutic target in gastrointestinal inflammation in the larger context of its general immunoregulatory role.

48. Neuropeptides as cell gene therapy in experimental autoimmune encephalomyelitis

Dendritic cells (DC) initiate immune responses as well as antigen-specific tolerance. We showed previously that the neuropeptide vasoactive intestinal peptide (VIP) suppresses innate immune responses, generates tolerogenic dendritic cells, and has therapeutic effects in models of autoimmune/inflammatory disorders. To generate tolerogenic DC that also provide VIP locally, we engineered VIP-expressing DC using lentiviral vectors. LentiVIP-DC secrete VIP, switch from a proinflammatory to an anti-inflammatory cytokine profile and lose the capacity to activate T cells. A single inoculation of LentiVIP-DC in models of experimental autoimmune encephalomyelitis (EAE) led to a reduction in clinical symptoms, associated with reduced expression of proinflammatory cytokines and increased levels of the anti-inflammatory cytokine IL-10 in the spinal cord of treated mice. Induction of antigen-specific regulatory T cells and local delivery of VIP by LentiVIP-DC may represent a promising therapeutic tool for the treatment of autoimmune diseases and inflammatory disorders.