title: Intraepithelial lymphocytes: exploring the Third Way in immunology.
abstract: Locally resident intraepithelial lymphocytes (IELs) are primarily T cells with potent cytolytic and immunoregulatory capacities, which they use to sustain epithelial integrity. Here, we consider that most IEL compartments comprise a variable mixture of two cell types: T cells primed to conventional antigen in the systemic compartment and T cells with ill-defined reactivities and origins, whose properties seem to place them mid-way between the adaptive and innate immune responses. We review the capacity of IELs to limit the dissemination of infectious pathogens and malignant cells and to control the infiltration of epithelial surfaces by systemic cells. An improved characterization of IELs would seem essential if we are to understand how immune responses and immunopathologies develop at body surfaces.
authors.affiliation: Peter Gorer Department of Immunobiology, GKT School of Medicine, University of London, Third floor New Guy's House, Guy's Hospital, London SE1 9RT, UK. adrian.hayday@kcl.ac.uk
authors.forename: A
authors.initials: A
authors.lastname: Hayday
authors.forename: E
authors.initials: E
authors.lastname: Theodoridis
authors.forename: E
authors.initials: E
authors.lastname: Ramsburg
authors.forename: J
authors.initials: J
authors.lastname: Shires
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000953:Antigens, Protozoan / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology; D015551:Autoimmunity; D001853:Bone Marrow / Q000196:embryology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000145:classification / Q000276:immunology; D002446:Celiac Disease / Q000276:immunology; D019070:Cell Lineage; D004848:Epithelium / Q000276:immunology*; D020869:Gene Expression Profiling; D015395:Histocompatibility Antigens Class I / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D007156:Immunologic Memory; D007239:Infections / Q000276:immunology; D007413:Intestinal Mucosa / Q000276:immunology; D007421:Intestine, Small / Q000276:immunology; D008099:Liver / Q000166:cytology / Q000196:embryology; D051379:Mice; D008819:Mice, Nude; D018448:Models, Immunological; D009928:Organ Specificity; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000032:analysis; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000032:analysis; D012867:Skin / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology / Q000196:embryology
chemical_list: D000953:Antigens, Protozoan; D000956:Antigens, Viral; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta