Alternative molecular form of human T cell-specific antigen CD27 expressed upon T cell activation.
The CD27 membrane antigen is exclusively present on a large subset of human peripheral blood T lymphocytes and on mature thymocytes. Several observations point towards a specific role of this molecule on activated T cells. Upon T cell activation induced via the T cell receptor complex, CD27 expression greatly increases, while addition of anti-CD27 monoclonal antibodies amplifies the proliferative response. Within the CD4+ subset, only CD27+ T cells provide helper activity for B cell differentiation. Interestingly, CD27 expression differs not only quantitatively, but also qualitatively between resting and activated T cells. On resting cells, CD27 is a disulfide-linked homodimer with subunits of 55 kDa molecular mass. Upon activation, also a 55-kDa monomer seems to occur, while in addition a 32-kDa component is found. The relationship between these two proteins has been investigated. The 55-kDa and 32-kDa molecules do not seem to be physically associated. The two CD27 components are structurally highly homologous as determined by two-dimensional mapping of tryptic peptides. They both express the epitopes recognized by anti-CD27 antibodies, indicating that the 32-kDa molecule is also T cell specific. Both 55-kDa and 32-kDa molecules carry N-linked carbohydrate groups. However, they differ in other, not yet specified, post-translational modifications, and do not arise from a common precursor simply by alternative N-glycosylation. The 32-kDa form may be derived by proteolytic processing from the 55-kDa protein, but most likely not from a larger (common) precursor. Alternatively, both molecules may arise from a common gene by alternative mRNA splicing, or be derived from highly homologous genes. The dramatic change in molecular composition of CD27 suggests a newly acquired function for CD27 on activated T cells.
Borst
J
J
Department of Immunology, The Netherlands Cancer Institute, Amsterdam.
Sluyser
C
C
De Vries
E
E
Klein
H
H
Melief
C J
CJ
Van Lier
R A
RA
D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis / Q000276:immunology / Q000302:isolation & purification*; D004220:Disulfides; D000939:Epitopes / Q000302:isolation & purification; D006801:Humans; D008213:Lymphocyte Activation; D008970:Molecular Weight; D011233:Precipitin Tests; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7
D000945:Antigens, Differentiation, T-Lymphocyte; D004220:Disulfides; D000939:Epitopes; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7