Characterization of cytoplasmic Form of Human CTLA - 4 Molecule.
- Author:
Yang Ja CHO
;
Yong Hoon CHUNG
;
Hyung Soo HAN
- Publication Type:Original Article
- Keywords:
CTLA-4;
Immunoprecipitation;
High MW protein complex
- MeSH:
Antigens, CD27;
Blotting, Western;
CTLA-4 Antigen;
Cytoplasm*;
Flow Cytometry;
Humans*;
Immunoprecipitation;
Lymphocytes;
Membranes;
Molecular Weight;
T-Lymphocytes;
Ultrafiltration
- From:Korean Journal of Immunology
1997;19(2):219-228
- CountryRepublic of Korea
- Language:Korean
-
Abstract:
CTLA-4 (=CD152), a T cell activation antigen, has been known to be homologous to CD28 in its molecular and genomic structure. Both of these two molecules are sharing their counterreceptors, B7 (CDSO) and B7-2 (CD86) and are known to play a crucial role in T cell activation. In previous our study it was reported that there are 2 forms of CTLA-4 antigen in activated human T cells, 30 kD membrane-bound form and 34 kD cytosolic-sequestered form and the former was less than 5 % of total of this antigen induced. Aims of this study are to confirm previous finding by using flow cytometry and to characterize the cytoplasmic form of human CTLA-4 by using ultrafiltration and immunoprecipitation techniques. In PHA stimulated peripheral blood lymphocyte surface expression of CTLA-4 was less than 2.1% of any of CD4+, CD8+ and CD56+ subsets. And the 34 kD form of CTLA-4 was detected in CDS+ subset only. This discrepancy confirms that 34 kD antigen is the cytoplasmic form of human CTLA-4. In ultrafiltration and subsequent Western blot analysis study this 34 kD antigen was detected in >100 kD fraction only. And in non-reducing condition this antigen formed high molecular weght complex (MW > 350 kD). In immunoprecipitation study using anti-peptide A antibody it was found that this high molecular weight complex consists of the 34 kD cytoplasmic form of CTLA-4 and previously unknown 54 kD antigen and 46 kD antigen at 1:1:8-10 ratio. And none of these 3 molecules were identified in membrane fraction of activated human T cell. The result of this study implies that CTLA-4 molecule induced upon T cell activation mainly sequestered in cytoplasrn and another signal is necessary to target this antigen on the activated T cell surface.
