title: Physical and functional association of CD45 and CD3-TCR complex on CD1+ human thymocytes. Evidence that the engagement of CD45 molecules can prevent CD1+ thymocytes from apoptosis.
abstract: In this study the effects of CD45 engagement on CD3-TCR-driven stimulation of CD1+ human immature thymocytes have been analyzed. Simultaneous cross-linking of CD45 and CD3 antigens on highly purified CD1+ thymocytes reduced the number of cells undergoing apoptosis after 16 h of in vitro culture. This cell population might represent immature thymocytes committed in vivo to die by programmed cell death (PCD). CD45 engagement could also increase the number of cycling CD1+ thymocytes; of note, the large majority (> 95%) of dividing cells expressed the CD1 molecule at the cell surface, indicating that proliferating cells were actually represented by immature thymocytes. These data suggest that the CD45 molecule might play a role in the rescue of immature thymocytes from PCD during differentiation. Along this line, we found that activation of CD1+ thymocytes via the CD3-TCR complex could be enhanced by CD45, both in terms of transcription and surface expression of IL-2R. These effects might be explained by the finding that the CD45 molecule (but not its isoforms CD45RO and RA) was physically associated with the CD3-TCR complex at the cell surface of CD1+ human thymocytes, as shown by co-precipitation and co-capping experiments. Finally, cross-linking of CD45 and CD3 antigens led to the expansion of CD3+ thymocytes co-expressing CD4 and CD8, indicating that simultaneous engagement of CD45 and CD3 molecules can block CD1+ cells at the double-positive (CD3+CD4+CD8+) differentiation stage. On the other hand, stimulation through CD3 resulted in the expansion of thymocytes showing a mature phenotype (CD3+CD4+ or CD3+CD8+). Altogether, these findings suggest that the CD45 molecule is involved both in early activation and in the regulation of CD1+ thymocyte differentiation.
authors.affiliation: Laboratory of Immunopathology, Instituto Nazionale per la Ricerca sul Cancro e Centro di Biotecnologie Avanzate, Genoa, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Poggi
authors.forename: N
authors.initials: N
authors.lastname: Pella
authors.forename: C
authors.initials: C
authors.lastname: Cantoni
authors.forename: M R
authors.initials: MR
authors.lastname: Zocchi
authors.forename: L
authors.initials: L
authors.lastname: Moretta
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018949:Antigens, CD1 / Q000032:analysis*; D017209:Apoptosis / Q000187:drug effects*; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000494:pharmacology; D006801:Humans; D017493:Leukocyte Common Antigens / Q000378:metabolism* / Q000494:pharmacology*; D011485:Protein Binding / Q000276:immunology; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism*; D016176:T-Lymphocyte Subsets / Q000187:drug effects* / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects* / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D018949:Antigens, CD1; D015704:CD4 Antigens; D016827:CD8 Antigens; D003432:Cross-Linking Reagents; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D017493:Leukocyte Common Antigens