title: New insights into the functions of alpha-MSH and related peptides in the immune system.
abstract: There is a substantial body of evidence that the tridecapeptide alpha-melanocyte-stimulating hormone (alpha-MSH) functions as a mediator of immunity and inflammation. The immunomodulating capacity of alpha-MSH is primarily because of its effects on melanocortin receptor (MC-1R)-expressing monocytes, macrophages, and dendritic cells (DCs). alpha-MSH down-regulates the production of proinflammatory and immunomodulating cytokines (IL-1, IL-6, TNF-alpha, IL-2, IFN-gamma, IL-4, IL-13) as well as the expression of costimulatory molecules (CD86, CD40, ICAM-1) on antigen-presenting DCs. In contrast, the production of the cytokine synthesis inhibitor IL-10 is up-regulated by alpha-MSH. At the molecular level, these effects of alpha-MSH are mediated via the inhibition of the activation of transcription factors such as NFkappaB. Not only alpha-MSH but also its C-terminal tripeptide (alpha-MSH 11-13, KPV) was able to bind to MC-1R and to modulate the function of APCs. In vivo, using a mouse model of contact hypersensitivity (CHS) systemic and topical application of alpha-MSH or KPV inhibited the sensitization and the elicitation phase of CHS and was able to induce hapten-specific tolerance. To investigate the underlying mechanisms of tolerance induction, we have performed in vivo transfer experiments. Treatment of naive mice with bone marrow-derived immature haptenized and alpha-MSH-pulsed DCs resulted in a significant inhibition of CHS. Furthermore, tolerance induction was found to be mediated by the generation of CTLA4(+) and IL-10-producing T lymphocytes. The potent capacity of alpha-MSH to modulate the function of antigen-presenting cells (APCs) has been further supported in another experimental approach. In vitro, by activating APCs, alpha-MSH has been shown to modulate IgE production by IL-4 and anti-CD40 stimulated B lymphocytes. Moreover, in a murine model of allergic airway inflammation, systemic treatment with alpha-MSH resulted in a significant reduction of allergen-specific IgE production, eosinophil influx, and IL-4 production. These effects were mediated via IL-10 production, because IL-10 knockout mice were resistant to alpha-MSH treatment. Therefore, therapeutic application of alpha-MSH or related peptides (KPVs) as well as alpha-MSH/KPV-pulsed DCs may be a useful approach for the treatment of inflammatory, autoimmune, and allergic diseases in the future.
authors.affiliation: Department of Dermatology and Ludwig Boltzmann Institute for Cell Biology and Immunobiology of the Skin, University of Münster, 48149 Münster, Germany. luger@uni-muenster.de
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Luger
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Scholzen
authors.forename: Thomas
authors.initials: T
authors.lastname: Brzoska
authors.forename: Markus
authors.initials: M
authors.lastname: Böhm
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology / Q000378:metabolism; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology / Q000378:metabolism; D007107:Immune System / Q000502:physiology*; D008214:Lymphocytes / Q000276:immunology / Q000378:metabolism; D010455:Peptides / Q000276:immunology* / Q000378:metabolism; D018043:Receptors, Corticotropin / Q000378:metabolism; D044101:Receptors, Melanocortin; D000521:alpha-MSH / Q000276:immunology* / Q000378:metabolism
chemical_list: D010455:Peptides; D018043:Receptors, Corticotropin; D044101:Receptors, Melanocortin; D000521:alpha-MSH