Changes in Arrangement and in Conformation of Molecular Components of Peripheral T‐Cell Antigen Receptor Complex After Ligand Binding: Analyses by Co‐Precipitation Profiles

Amounts of co‐precipitating CD3 components by anti‐T‐cell receptor (TCR)Vβ or anti‐CD4/8 monoclonal antibodies were compared between non‐stimulated and stimulated splenic T cells. The amounts of co‐precipitating CD3δ, ε and γ chains with TCRαβ and with CD4/8 were not significantly changed after TCR ligation. The apparent amount of CD3ζ chain co‐precipitated with TCRαβ increased up to threefold, while the actual amount of co‐precipitating CD3ζ with TCRαβ and the total amount of specifically precipitated CD3ζ are not changed after cross linking of TCR. The apparent amount of CD3ζ chain co‐precipitated with CD4/8 also increased. Unlike co‐precipitation with TCRαβ, the actual amount of CD3ζ co‐precipitated with CD4/8 increased significantly. This observation suggests a conformational change as well as the relocation of CD3ζ molecules within the TCR complex after the signal delivery. After TCR ligation, CD3ζ chains relocate to the vicinity of either CD4 or CD8 molecules. In addition, when cross linking and binding signals are compared, CD3 chains undergo two distinct phases of conformational change. The early conformational change caused by ligand binding is positively related to the induction of proliferative responses, while the later conformational change caused by the cross linking of TCR does not induce but enhances the proliferative response.