T-cel l Receptor P-Chain Gene Rearrangement and Expression During Human Thymic Ontogenesis

By Antonio Bonati, Paola Zanelli, Sergio Ferrari, Anna Plebani, Bruno Starcich, Mario Savi, and Tauro M. Neri T-cell ,receptor (TCR) @chain proteins appear early ( 15th week of gestation) during human thymic ontogenesis. These p-chain proteins, which appear before terminal deoxynucleotidyl transferase (TdT), could be an expression of a fully rearranged (V-D-J), incompletely rearranged (D-J), or germline TCR p-chain gene. The aims of this study, performed from the 15th week onward, were the following: (1) to investigate whether or not TCR p gene rearranges at an early stage during human thymic ontogenesis; (2) to investigate whether complete presumptive functional (1.3 kb) TCR f3 gene transcript is present at these early stages of development, or if incomplete (1 kb) or germ-line (1.1 kb) transcripts are expressed; (3) to examine the phenotype of TCR kchain' cells with two-color fluorescence using monoclonal antibody (MoAb) f3Fl and MoAbs that recognize CD1, CD2, CD3, CD4, CD8, CD5, and CD7 antigens (rabbit anti-calf TdT antiserum was used to detect TdT); and (4) to demonstrate whether or not f3 gene N-diversity regions are detectable as early as the 15th week and whether or not N-nucleotide insertions correlate to TdT expression. Fifteento 22-week fetal thymuses and pediatric thymuses were investigated. We demonstrated that TCR p-chain gene rearranged as early as the 15th week