title: Role of major histocompatibility complex class II expression by non-hematopoietic cells in autoimmune and inflammatory disorders: facts and fiction.
abstract: It is well established that interactions between CD4(+) T cells and major histocompatibility complex class II (MHCII) positive antigen-presenting cells (APCs) of hematopoietic origin play key roles in both the maintenance of tolerance and the initiation and development of autoimmune and inflammatory disorders. In sharp contrast, despite nearly three decades of intensive research, the functional relevance of MHCII expression by non-hematopoietic tissue-resident cells has remained obscure. The widespread assumption that MHCII expression by non-hematopoietic APCs has an impact on autoimmune and inflammatory diseases has in most instances neither been confirmed nor excluded by indisputable in vivo data. Here we review and put into perspective conflicting in vitro and in vivo results on the putative impact of MHCII expression by non-hematopoietic APCs--in both target organs and secondary lymphoid tissues--on the initiation and development of representative autoimmune and inflammatory disorders. Emphasis will be placed on the lacunar status of our knowledge in this field. We also discuss new mouse models--developed on the basis of our understanding of the molecular mechanisms that regulate MHCII expression--that constitute valuable tools for filling the severe gaps in our knowledge on the functions of non-hematopoietic APCs in inflammatory conditions.
authors.affiliation: Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: F V
authors.initials: FV
authors.lastname: Duraes
authors.forename: C
authors.initials: C
authors.lastname: Thelemann
authors.forename: K
authors.initials: K
authors.lastname: Sarter
authors.forename: H
authors.initials: H
authors.lastname: Acha-Orbea
authors.forename: S
authors.initials: S
authors.lastname: Hugues
authors.forename: W
authors.initials: W
authors.lastname: Reith
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D001327:Autoimmune Diseases / Q000276:immunology* / Q000473:pathology; D004195:Disease Models, Animal; D006413:Hematopoietic System / Q000276:immunology* / Q000473:pathology*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D007249:Inflammation / Q000276:immunology* / Q000473:pathology; D009928:Organ Specificity / Q000276:immunology
chemical_list: D000949:Histocompatibility Antigens Class II