title: Cloning of a novel MHC-encoded serine peptidase highly expressed by cortical epithelial cells of the thymus.
abstract: Antigen presentation by cortical thymic epithelial cells (cTEC) during the positive selection of T cells has been shown to differ from that of other antigen-presenting cells. In the case of MHC class II presentation, cathepsin L as opposed to cathepsin S is responsible at least in part for the degradation of invariant chain. Other proteases, however, must be involved. We have identified a putative serine protease that is specifically expressed in the thymus. Encoded within the class I major histocompatibility complex (MHC) region, this gene has sequence homology with lysosomal prolylcarboxypeptidase, suggesting that it is a serine protease. We have, therefore, designated this gene thymus-specific serine protease (TSSP). In situ hybridization and immunofluorescence staining reveal that TSSP is expressed exclusively by cortical thymic epithelial cells, with the strongest staining noted around vessels and the thymic capsule. The identification of TSSP further supports the theory that MHC class II antigen processing and presentation in the thymic cortex involves a proteolytic milieu that differs from that of other antigen-presenting cells.
authors.affiliation: Department of Internal Medicine, University of California Davis Medical Center, Sacramento, California 95817, USA. clbowlus@ucdavis.edu
authors.forename: C L
authors.initials: CL
authors.lastname: Bowlus
authors.forename: J
authors.initials: J
authors.lastname: Ahn
authors.forename: T
authors.initials: T
authors.lastname: Chu
authors.forename: J R
authors.initials: JR
authors.lastname: Gruen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D001483:Base Sequence; D002268:Carboxypeptidases / Q000737:chemistry; D016384:Consensus Sequence; D003360:Cosmids; D004847:Epithelial Cells / Q000201:enzymology; D019084:Fluorescent Antibody Technique, Indirect; D005796:Genes; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D017403:In Situ Hybridization; D008247:Lysosomes / Q000201:enzymology; D008285:Major Histocompatibility Complex / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000235:genetics* / Q000302:isolation & purification; D013950:Thymus Gland / Q000201:enzymology* / Q000254:growth & development
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D002268:Carboxypeptidases; C022448:lysosomal Pro-X carboxypeptidase; D012697:Serine Endopeptidases