ROSETTI NG OF ACTI VATED HUMAN T LYMPHOCYTES W I TH AUTOLOGOUS ERYTHROCYTES Def i ni t i on of t he Recept or and Li gand Mol ecul es as CD2 and Lymphocyt e Funct i on- associ at ed Ant i gen 3 ( LFA- 3) By MARI AN L . PLUNKETT, MARTI N E. SANDERS, * PERI ASAMY SELVARAJ , MI CHAEL L . DUSTI N, AND TI MOTHY A . SPRI NGER Fr om t he Labor at or y of Membr ane I mmunochem i st r y, Dana- Far ber Cancer I nst i t ut e, and Depart ment of Pat hol ogy, Har var d Medi cal School , Bost on, Massachuset t s 02115 and t he *I mmunol ogy Br anch, Nat i onal Cancer I nst i t ut e, Nat i onal I nst i t ut es of Heal t h, Bet hesda, Maryl and 20892 CD2 ( known al so as T 11 [ 1] , LFA- 2 [ 2, 3] , and t he E r oset t e r ecept or [ 4] ) is a T l ymphocyt e sur f ace gl ycopr ot ei n of 50- 58 kD t hat appear s ear l y in t hymocyt e ont ogeny and is pr esent on al l mat ure T cel l s ( 5) . mAbs to CD2 i nhi bi t Th cel l ant i gen-st i mul at ed pr ol i f er at i on and cyt ol yt i c T l ymphocyt e-medi at ed ki l l i ng ( 2- 4, 6) . CD2 mAbs i nhi bi t an ear l y st ep in T l ymphocyt e-medi at ed ki l l i ng, adhesi on of t he T l ymphocyt e to t he t ar get cel l ( 7) . The f i ndi ngs suggest t hat CD2-medi at ed adhesi on f aci l i t at es i nt er act i on of T l ymphocyt es with ot her cel l s . Cur i ousl y, CD2 mAbs al so i nhi bi t r oset t i ng of T l ymphocyt es with E ( 4, 8) . When human T l ymphocyt es ar e cent r i f uged with E of cer t ai n speci es and hel d at 4' C, t hey ar e f ound to adher e to mul t i pl e E in del i cat e r oset t es ( 9, 10) . Roset t i ng has l ong been used to pur i f y T l ymphocyt es f r om per i pher al bl ood, and cl i ni cal l y to enumerat e T l ymphocyt e subpopul at i ons ( 11) . Roset t i ng does not i nvol ve t he T cel l ant i gen r ecept or . Sheep E r oset t e with essent i al l y al l human T l ymphocyt es in per i pher al bl ood and with t hymocyt es and act i vat ed T l ym- phocyt es ( 9) . A smal l per cent age of human per i pher al bl ood T l ymphocyt es will f or m aut ol ogous r oset t es with human E ( 12- 14) . Roset t i ng with aut ol ogous and al l ogenei c E is equi val ent . The subpopul at i on t hat f orms aut ol ogous r oset t es medi at es t he aut ol ogous MLR ( 12, 15) and may t hus be act i vat ed . Act i vat ed human T l ymphocyt es, i .e ., t hymocyt es, T l ymphobl ast s, and T cel l t umor l i nes, vi gor ousl y r oset t e with human E ( 16) . Roset t i ng of human T l ymphocyt es with E f r om sheep, human, pi g, and r abbi t is i nhi bi t ed by CD2 mAbs ( 8, 13, 17, 18) , and t hus it has been i nf er r ed t hat CD2 is an E r oset t e r ecept or . We r ecent l y pur i f i ed CD2 to homogenei t y and f ound t hat it i nhi bi t ed sheep E r oset t i ng and was absor bed by sheep E ( 19) . Thi s suggest ed to us t hat CD2 m i ght bi nd to a si m i l ar l i gand on human E. We have pr evi ousl y def i ned ( 3, 20) an ant i gen- i ndependent pat hway of T l ymphocyt e adhesi on to t ar get cel l s t hat i nvol ves CD2 on t he T l ymphocyt e and Thi s wor k was suppor t ed by Nat i onal I nst i t ut es of Heal t h gr ant CA- 31798 and an Amer i can Cancer Soci et y Facul t y Awar d to T. A . Spr i nger . 664 Jour nal of Experi ment al Medi ci ne - Vol ume 165, Mar ch 1987 664- 676 on November 30, 2015 jem.rupress.org Downloaded from Published March 1, 1987