UVA1 radiation attenuates pro-inflammatory functions in human monocytes.

UVA1 therapy is effective in the treatment of inflammatory and autoimmune skin diseases. The mode of action of UVA1 therapy is not completely understood and especially data on cells of the innate immune system like monocytes, which are critically involved in many inflammatory processes, are sparse. We wanted to answer the question whether UVA1 irradiation alters functional properties of human monocytes. We treated human peripheral blood monocytes in vitro with 2 J/cm2 UVA1 light, incubated the cells for 48 h and examined both functional properties and alterations in the gene and protein expression profile. While UVA1 did not alter cell viability or susceptibility to apoptosis inducing agents, it decreased the capacity of monocytes for phagocytosis and to eliminate infectious agents like Leishmania major. Moreover, we measured a significantly reduced production of interleukin (IL)-1ß mRNA in lipopolysaccharide activated monocytes after UVA1 treatment. Importantly, UVA1-treated monocytes not only produce less IL-1ß, but also upregulate expression of the anti-inflammatory IL-1ß decoy receptor. Our data provide evidence that UVA1 radiation not only interferes with fundamental monocyte properties like phagocytosis, pathogen killing and activation, but could also specifically attenuate pro-inflammatory IL-1 effects. This might constitute a hitherto unknown anti-inflammatory mechanism of UVA1 in human monocytes.

Aryl Hydrocarbon Receptor-Signaling Regulates Early Leishmania major-Induced Cytokine Expression.

The early inflammatory skin micromilieu affects resistance in experimental infection with Leishmania major. We pursue the concept that macrophages, which take up parasites during early infection, exert decisive influence on the inflammatory micromilieu after infection. In order to analyze their distinctive potential, we identified differentially regulated genes of murine granuloma macrophages (GMΦ) from resistant and susceptible mice after their infection with metacyclic Leishmania major. We found induction of several cytokines in GMΦ from both strains and a stronger upregulation of the transcription factor aryl hydrocarbon receptor (AhR) in GMΦ from resistant mice. Using both an AhR agonist and antagonist we demonstrated that AhR is involved in Leishmania-induced production of TNF in macrophages. In vivo, single local injection of an AhR agonist in early lesions of susceptible mice caused an increased induction of Tnf and other cytokines in the skin. Importantly, local agonist treatment led to a reduction of disease severity, reduced parasite loads and a weaker Th2 response. Our results demonstrate that local activation of AhR has a beneficial effect in experimental leishmaniasis.

Epidermal expression of I-TAC (Cxcl11) instructs adaptive Th2-type immunity.

To decipher early promoters of the local microenvironment for Th2-type immunity, we wanted to identify gene patterns that were induced by Leishmania major in the infected skin of susceptible, Th2-prone BALB/c, but not of resistant, Th1-prone C57BL/6 mice. We found a marked up-regulation of the chemokine I-TAC (Cxcl11) during the first 2 d of infection in the epidermis of susceptible but not of resistant mice. Accordingly, local injection of I-TAC (2×1 µg) in resistant mice on the first day of infection resulted in a Th2-driven, sustained deterioration of disease and dramatically enhanced parasite levels. On the cellular level, I-TAC decreased IL-12 production by dendritic cells (DCs) in skin-draining lymph nodes and by DCs in vitro. Thus, we demonstrate for the first time that epidermis-derived I-TAC triggers a sustained Th2-response that determines the outcome of a complex immunological process.

IκBζ is a transcriptional key regulator of CCL2/MCP-1.

CCL2, also referred to as MCP-1, is critically involved in directing the migration of blood monocytes to sites of inflammation. Consequently, excessive CCL2 secretion has been linked to many inflammatory diseases, whereas a lack of expression severely impairs immune responsiveness. We demonstrate that IκBζ, an atypical IκB family member and transcriptional coactivator required for the selective expression of a subset of NF-κB target genes, is a key activator of the Ccl2 gene. IκBζ-deficient macrophages exhibited impaired secretion of CCL2 when challenged with diverse inflammatory stimuli, such as LPS or peptidoglycan. These findings were reflected at the level of Ccl2 gene expression, which was tightly coupled to the presence of IκBζ. Moreover, mechanistic insights acquired by chromatin immunoprecipitation demonstrate that IκBζ is directly recruited to the proximal promoter region of the Ccl2 gene and is required for transcription-enhancing histone H3 at lysine-4 trimethylation. Finally, IκBζ-deficient mice showed significantly impaired CCL2 secretion and monocyte infiltration in an experimental model of peritonitis. Together, these findings suggest a distinguished role of IκBζ in mediating the targeted recruitment of monocytes in response to local inflammatory events.

Keratinocytes determine Th1 immunity during early experimental leishmaniasis.

Experimental leishmaniasis is an excellent model system for analyzing Th1/Th2 differentiation. Resistance to Leishmania (L.) major depends on the development of a L. major specific Th1 response, while Th2 differentiation results in susceptibility. There is growing evidence that the microenvironment of the early affected tissue delivers the initial triggers for Th-cell differentiation. To analyze this we studied differential gene expression in infected skin of resistant and susceptible mice 16h after parasite inoculation. Employing microarray technology, bioinformatics, laser-microdissection and in-situ-hybridization we found that the epidermis was the major source of immunomodulatory mediators. This epidermal gene induction was significantly stronger in resistant mice especially for several genes known to promote Th1 differentiation (IL-12, IL-1beta, osteopontin, IL-4) and for IL-6. Expression of these cytokines was temporally restricted to the crucial time of Th1/2 differentiation. Moreover, we revealed a stronger epidermal up-regulation of IL-6 in the epidermis of resistant mice. Accordingly, early local neutralization of IL-4 in resistant mice resulted in a Th2 switch and mice with a selective IL-6 deficiency in non-hematopoietic cells showed a Th2 switch and dramatic deterioration of disease. Thus, our data indicate for the first time that epidermal cytokine expression is a decisive factor in the generation of protective Th1 immunity and contributes to the outcome of infection with this important human pathogen.