A novel 120-kDa antigen shared by immature human thymocytes and long-term-activated T cells.
In this study we report the characterization of monoclonal antibody (mAb) 8B4/20, raised against immature human thymocytes, that identifies a novel leukocyte antigen. The molecular characterization of the antigen by immunoprecipitation and immunoblotting yields, under nonreducing conditions, a specific band of 120 kDa which, under reducing conditions, displays a slightly lower molecular mass (110 kDa. mAb 8B4/20 detects a molecule found on the majority of thymocytes with an inverted gradient of expression when compared to CD3. It appears at high density on the CD3-/low thymocytes, at reduced density on the CD3med and double-positive thymocytes, and is absent on CD3hi and single-positive thymocytes and on peripheral blood T cells. Immunohistochemistry on frozen sections demonstrates cortical staining of the thymic lobules. Flow cytometric analysis of the different subsets of peripheral blood mononuclear cells shows that mAb 8B4/20 detects an antigen expressed only on CD56+/CD16+ natural killer cells and on a fraction of CD14+ monocytes. T cells, B cells, erythrocytes, granulocytes and platelets are consistently negative. The expression of the molecule on tumor cell lines does not show lineage restriction. Analysis of phytohemagglutinin plus recombinant interleukin-2-activated peripheral blood lymphocytes shows that mAb 8B4/20 identifies an antigen expressed on CD3+ cells by week 3 of culture. Thus, it recognizes a very late activation antigen (VLA) on mature T cells. The cell distribution and the electrophoretic pattern of the molecule identified by mAb 8B4/20 is distinct from that of known CD and of integrin/VLA molecules. Its function on thymocytes is so far unknown; however, the binding of mAb 8B4/20 to tumor lines induces changes in the morphology and adhesive properties of the 8B4/20+ cells growing in suspension. We suggest that mAb 8B4/20 recognizes a molecule that may be involved in interactions between thymocytes and other thymic structures that may be relevant for the selection process.
Fabbi
M
M
IST, Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy.
Tiso
M
M
Gangemi
R M
RM
Favre
A
A
Demartini
P
P
Bargellesi-Severi
A
A
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000737:chemistry*; D002448:Cell Adhesion / Q000502:physiology; D002478:Cells, Cultured; D002675:Child, Preschool; D005333:Fetus / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007223:Infant; D007231:Infant, Newborn; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D011233:Precipitin Tests; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000196:embryology / Q000276:immunology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface