Engagement of CD99 induces up-regulation of TCR and MHC class I and II molecules on the surface of human thymocytes.
CD99 is a cell surface molecule involved in the aggregation of lymphocytes and apoptosis of immature cortical thymocytes. Despite its high level expression on immature cortical thymocytes, the functional roles of this molecule during thymic selection are only now being elucidated. Examination of the effects of CD99 engagement on the expression kinetics of the TCR and MHC class I and II molecules, which are involved primarily in thymic positive selection, revealed a marked up-regulation of these proteins on the surface of immature thymocytes. This increase was the result of accelerated mobilization of molecules stored in cytosolic compartments to the plasma membrane, rather than increased RNA and protein synthesis. Confocal microscopic analysis revealed the changes in subcellular distribution of these molecules. When CD99 was engaged, TCR and MHC class I and II molecules were concentrated at the plasma membrane, particularly at cell-cell contact sites. The TCRlow subpopulation of immature double positive thymocytes was much more responsive to CD99-mediated up-regulation than was the TCRhigh population. These findings suggest that CD99-dependent up-regulation may have possible implication in positive selection during thymocyte ontogeny.
Department of Pathology, Seoul National University College of Medicine, Korea.
E Y
EY
Choi
W S
WS
Park
K C
KC
Jung
S H
SH
Kim
Y Y
YY
Kim
W J
WJ
Lee
S H
SH
Park
D000071443:12E7 Antigen; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000276:immunology / Q000502:physiology*; D002449:Cell Aggregation / Q000276:immunology; D002454:Cell Differentiation / Q000276:immunology; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000276:immunology / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000096:biosynthesis / Q000378:metabolism*; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D015854:Up-Regulation / Q000276:immunology*
D000071443:12E7 Antigen; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D011948:Receptors, Antigen, T-Cell