title: Expression of a nonclassical MHC class Ib molecule in the eye.
abstract: BACKGROUND
  MHC class Ia molecules are absent, or expressed at low levels, on cells lining the anterior chamber of the eye, an immune-privileged site. Although the scarcity of class Ia MHC antigens may protect cells from T cell-mediated tissue injury, it may also render them vulnerable to natural killer cell-mediated cytolysis. There is growing evidence that MHC class Ib molecules share similar functions to class Ia. In this study, we examine the expression and distribution of Qa-2, one of the best-characterized murine MHC class Ib molecules in the eye.
  
  
  METHODS
  The transcription of Qa-2 mRNA in whole eye and eye-derived cells was analyzed by sensitive and specific RNase protection and reverse transcription-polymerase chain reaction assays. Immunohistochemistry, flow cytometry, and ELISA were used to determine whether Qa-2 was expressed as cell surface proteins. Expression levels of Qa-2 were monitored in resting cells and cells stimulated with interferon-gamma.
  
  
  RESULTS
  Expression of membrane-bound and soluble Qa-2 isoforms was detected in various tissues of the eye, including cell subsets lining the anterior chamber. Immunohistological staining revealed Qa-2 expression on corneal epithelium as well as endothelium, iris ciliary bodies, and retina. These observations were confirmed by analysis of cultured, eye-derived cells. Qa-2 expression was inducible by interferon-gamma. Qa-2 was not detected in lens cells.
  
  
  CONCLUSIONS
  The results demonstrate that membrane-bound and soluble MHC class Ib molecules are expressed by eye cells. Expression of Qa-2 in the corneal endothelium and other substructures lining the anterior chamber suggests that this class Ib protein may contribute to the immune-privileged status of the anterior chamber.
authors.affiliation: Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: J Y
authors.initials: JY
authors.lastname: Niederkorn
authors.forename: E Y
authors.initials: EY
authors.lastname: Chiang
authors.forename: T
authors.initials: T
authors.lastname: Ungchusri
authors.forename: I
authors.initials: I
authors.lastname: Stroynowski
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005123:Eye / Q000166:cytology / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D013045:Species Specificity; D014018:Tissue Distribution; D014158:Transcription, Genetic
chemical_list: D015395:Histocompatibility Antigens Class I; D020033:Protein Isoforms; C032907:Q surface antigens