摘要：

TheT11(CD2)sheep-erythrocyte-binding protein isaT-cell surface molecule involved inactivation ofT lymphocytes andthymocytes, including those lacking theT3-Ti antigen-receptor complex. Theprimary structure ofTilwas deduced fromprotein microsequencing andcDNAcloning. The maturehumanprotein appears tobedivided intothree domains: ahydrophilic 185aminoacid external domain bear- ingonlylimited homology totheT-cell surface protein T4and theimmunoglobulin Klight chain variable region, a25amino acidhydrophobic transmembrane segment, anda126amino acidcytoplasmic domain richinprolines andbasic residues. Transfection ofcDNAsencoding either the1.7- orthe1.3- kilobase TilmRNA into COS-1cells resulted inexpression of surface Tilepitopes aswellassheep-erythrocyte-binding capacity. Thepredicted structure isconsistent withthepossi- bility thatTilfunctions insignal transduction. Humanthymus-derived (T)lymphocytes wereoriginally distinguished fromBlymphocytes andother hematopoietic cells bytheir ability toformspontaneous aggregates (E rosettes) withsheep erythrocytes (SRBCs) (1-3). Congenital hypoplasia ofthethymus results inloss orsignificant dimi- nution ofperipheral bloodE-rosette-forming cells, thus

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