8B4/20, a private CD43 epitope on developing human thymocytes, is involved in thymocyte maturation.
The 8B4/20 Ag is a 120-kDa molecule whose expression on human thymocytes varies according to the differentiation stage: high density on immature CD3-/low thymocytes, reduced density on CD3medium and double-positive thymocytes, and absent on CD3high and single-positive thymocytes and on circulating T cells. In this paper we present immunological and biochemical evidence demonstrating that 8B4/20 Ag is a variant of CD43. We show that 8B4/20-expressing molecules, which are a subset of the CD43 molecules on thymocytes, are heterogeneous in charge, suggesting varying sialylation levels. The 8B4/20 epitope was mapped to the peripherally exposed N-terminal region of CD43, and the 8B4/20 antigenic determinant was characterized by requirement for the sialic acid exocyclic polyhydroxyl side chain, a feature shared with ligands of CD22. Altogether, 8B4/20-CD43 expression pattern and biochemical characteristics suggest its participation in carbohydrate-based interactions in the thymus. We therefore used specific Ab to mimic putative 8B4/20 interactions with natural ligand and examined the effect on isolated thymocytes. Treatment with 8B4/20 had no effect on in vitro apoptosis of isolated thymocytes. In contrast, 8B4/20 ligation enhanced the conversion of isolated thymocytes to differentiated phenotypes. Increased numbers were found in 8B4/20-treated cultures of CD3high and single-positive thymocytes and decreased numbers of CD3-/low and double-positive thymocytes, strongly suggesting that engagement of 8B4/20 delivers a positive signal that favors completion of the thymocyte maturation program. The ability of 8B4/20 mAb to drive thymocyte maturation in vitro suggests that CD43 molecules bearing the 8B4/20 epitope participate in early events of thymic selection.
Fabbi
M
M
Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy. fabbi@ermes.cba.unige.it
Geginat
J
J
Tiso
M
M
Ramarli
D
D
Parent
D
D
Bargellesi
A
A
Remold-O'Donnell
E
E
D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D000940:Antigenic Variation; D015703:Antigens, CD / Q000276:immunology*; D017209:Apoptosis; D002454:Cell Differentiation; D002469:Cell Separation; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D006801:Humans; D051917:Leukosialin; D016131:Lymphocyte Subsets / Q000276:immunology; D012795:Sialoglycoproteins / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018984:Epitopes, T-Lymphocyte; D051917:Leukosialin; C465014:SPN protein, human; D012795:Sialoglycoproteins