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The regulation of T cell proliferation and differentiation
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The Scientific & Social Program: Vth ISDCI Congress
PL2 THE REGULATION OF T CELL PROLIFERATION AND DIFFERENTIATION. Kendall A. Smith, Dartmouth Medical School, Hanover, NH 03756 T cell proliferation after antigen activation is a simple process, in that only two cell surface receptors signal all of the events that determine cell cycle progression. The T cell antigen receptor complex (TCR/CD3) moves the cell from Go Into the early (31 phase, which renders the cells "competent" to respo'~d to the T cell ~rowth factor, interleukin 2(IL-2). G1 "progression" to the S phase is dependent on only 3 variables, the IL-2 concentration, the IL-2 receptor density, and the duration of the IL-2/IL-2R interaction. These components determine a threshold of ~ln,000 IL-2/IL-2R interactions that ultimately make the quantal decision to proceed to DHA replication. In recent experiments we have developed methods to isolate and cl¢,ne IL-2-induced immediate/early genes, to begin to identify the molecular basis ol the IL-2/IL-2R threshold. Thus far, we have identified 8 novel IL-2-induced genes that we are characterizing. In other experiments, we have shown that the cellular prolo-oncogene c-rat-l, which codes for a serine/threonine kinase Is induced by IL-2 and also activated by IL-2, so that just prior to S phase, its activity is Induced 25-50-fold. T cell differentiation from an unprimed, naive T cell to a memory T cell is also dependent upon IL-2 stimulation. Naive T cells isolated from umbilical cord blood respond to activation of the TCR/CD3 complex by producing IL-2 and expressing IL-2 receptors, but they do not produce any other lymphokines. By comparison, memory T cells isolated from adults, express an entire lymphokine repertoire, including IL-2 IL-6, IFN-~A and GM-CSF immediately upon TCR/CD3 activation. Most important, naive T cells can be primed in vitro by stimulation via the TCR/CD3 complex and the IL-2 receptor to undergo a difterentiative switch, so that upon secondary stimulation a memory lymphokine repertoire is expressed.
PL3 FETAL-MATERNAL IMMUNE INTERACTION "D.W.Dresser and N . E . H e r r e r a . N a t i o n a l I n s t i t u t e for M e d i c a l R e s e a r c h , L o n d o n NW7 IAA, UK. In the late 1940's it b e c a m e c l e a r t h a t t h e h o m o g r a f t r e a c t i o n was e s s e n t i a l l y the r e s u l t of an i m m u n e response. S u b s e q u e n t l y M e d a w a r c o m m e n t e d on the a p p a r e n t p a r a d o x of t h e s u r v i v a l of the m a m m a l i a n fetus in t h e face of such a p o t e n t i a l (cell m e d i a t e d ) i m m u n e response. In an o u t b r e d p o p u l a t i o n the f e t a l - p l a c e n t a l unit w i l l be a n t i g e n i c a l l y d i f f e r e n t to the m o t h e r by v i r t u e of its c o m p l e m e n t of p a t e r n a l g e n e s and a d d i t i o n a l l y t h e r e m a y be d e v e l o p m e n t a l or s t a g e s p e c i f i c g e n e p r o d u c t s w h i c h are i m m u n o g e n i c . Many m e c h a n i s m s h a v e b e e n p r o p o s e d to a c c o u n t for the s u r v i v a l of the fetus in the face of a p o t e n t i a l i m m u n e a t t a c k and w h i l e m a n y of t h e s e h a v e b e e n i n v e s t i g a t e d in c o n s i d e r a b l e detail, t h e r e has b e e n no c l e a r cut i n d i c a t i o n that any one is p r e d o m i n a n t . E i t h e r c o n t r o l is e x e r c i s e d by an as yet u n d i s c o v e r e d m e c h a n i s m or m o r e p r o b a b l y by a c o m b i n a t i o n of s o m e or all of t h o s e w h i c h h a v e b e e n proposed. P o t e n t i a l c o n t r o l l i n g p r o c e s s e s , w h i c h will be r e v i e w e d b r i e f l y , include; s y s t e m i c and local m o d i f i c a t i o n of m a t e r n a l r e s p o n s i v e n e s s ; a l t e r e d e x p r e s s i o n of M H C a n t i g e n s on e m b r y o n i c t i s s u e s ; the p l a c e n t a as a b a r r i e r ; and b l o c k i n g a n t i b o d y r e s p o n s e s . W i t h r e s p e c t to this last topic, we shall d i s c u s s in g r e a t e r detail, r e c e n t s t u d i e s in w h i c h we have s t a r t e d to look for p o t e n t i a l b l o c k i n g a n t i b o d i e s in a m o u s e m o d e l system. A s c a l e d - d o w n v e r s i o n of the h y b r i d o m a t e c h n i q u e has b e e n u s e d as an a n a l y t i c a l p r o b e of the s p e c i f i c i t y and i s o t y p e of i m m u n o g l o b u l i n s e c r e t e d by cells o r i g i n a l l y s i t u a t e d e i t h e r c l o s e to the m i d - g e s t a t i o n m o u s e e m b r y o or in the l y m p h n o d e s (PALN) d r a i n i n g the p r e g n a n t uterus. Some monoclonal a n t i b o d i e s w i t h s p e c i f i c i t y for e m b r y o s and e x t r a - e m b r y o n i c m e m b r a n e s have b e e n derived.
The Scientific & Social Program: Vth ISDCI Congress
PL2 THE REGULATION OF T CELL PROLIFERATION AND DIFFERENTIATION. Kendall A. Smith, Dartmouth Medical School, Hanover, NH 03756 T cell proliferation after antigen activation is a simple process, in that only two cell surface receptors signal all of the events that determine cell cycle progression. The T cell antigen receptor complex (TCR/CD3) moves the cell from Go Into the early (31 phase, which renders the cells "competent" to respo'~d to the T cell ~rowth factor, interleukin 2(IL-2). G1 "progression" to the S phase is dependent on only 3 variables, the IL-2 concentration, the IL-2 receptor density, and the duration of the IL-2/IL-2R interaction. These components determine a threshold of ~ln,000 IL-2/IL-2R interactions that ultimately make the quantal decision to proceed to DHA replication. In recent experiments we have developed methods to isolate and cl¢,ne IL-2-induced immediate/early genes, to begin to identify the molecular basis ol the IL-2/IL-2R threshold. Thus far, we have identified 8 novel IL-2-induced genes that we are characterizing. In other experiments, we have shown that the cellular prolo-oncogene c-rat-l, which codes for a serine/threonine kinase Is induced by IL-2 and also activated by IL-2, so that just prior to S phase, its activity is Induced 25-50-fold. T cell differentiation from an unprimed, naive T cell to a memory T cell is also dependent upon IL-2 stimulation. Naive T cells isolated from umbilical cord blood respond to activation of the TCR/CD3 complex by producing IL-2 and expressing IL-2 receptors, but they do not produce any other lymphokines. By comparison, memory T cells isolated from adults, express an entire lymphokine repertoire, including IL-2 IL-6, IFN-~A and GM-CSF immediately upon TCR/CD3 activation. Most important, naive T cells can be primed in vitro by stimulation via the TCR/CD3 complex and the IL-2 receptor to undergo a difterentiative switch, so that upon secondary stimulation a memory lymphokine repertoire is expressed.
PL3 FETAL-MATERNAL IMMUNE INTERACTION "D.W.Dresser and N . E . H e r r e r a . N a t i o n a l I n s t i t u t e for M e d i c a l R e s e a r c h , L o n d o n NW7 IAA, UK. In the late 1940's it b e c a m e c l e a r t h a t t h e h o m o g r a f t r e a c t i o n was e s s e n t i a l l y the r e s u l t of an i m m u n e response. S u b s e q u e n t l y M e d a w a r c o m m e n t e d on the a p p a r e n t p a r a d o x of t h e s u r v i v a l of the m a m m a l i a n fetus in t h e face of such a p o t e n t i a l (cell m e d i a t e d ) i m m u n e response. In an o u t b r e d p o p u l a t i o n the f e t a l - p l a c e n t a l unit w i l l be a n t i g e n i c a l l y d i f f e r e n t to the m o t h e r by v i r t u e of its c o m p l e m e n t of p a t e r n a l g e n e s and a d d i t i o n a l l y t h e r e m a y be d e v e l o p m e n t a l or s t a g e s p e c i f i c g e n e p r o d u c t s w h i c h are i m m u n o g e n i c . Many m e c h a n i s m s h a v e b e e n p r o p o s e d to a c c o u n t for the s u r v i v a l of the fetus in the face of a p o t e n t i a l i m m u n e a t t a c k and w h i l e m a n y of t h e s e h a v e b e e n i n v e s t i g a t e d in c o n s i d e r a b l e detail, t h e r e has b e e n no c l e a r cut i n d i c a t i o n that any one is p r e d o m i n a n t . E i t h e r c o n t r o l is e x e r c i s e d by an as yet u n d i s c o v e r e d m e c h a n i s m or m o r e p r o b a b l y by a c o m b i n a t i o n of s o m e or all of t h o s e w h i c h h a v e b e e n proposed. P o t e n t i a l c o n t r o l l i n g p r o c e s s e s , w h i c h will be r e v i e w e d b r i e f l y , include; s y s t e m i c and local m o d i f i c a t i o n of m a t e r n a l r e s p o n s i v e n e s s ; a l t e r e d e x p r e s s i o n of M H C a n t i g e n s on e m b r y o n i c t i s s u e s ; the p l a c e n t a as a b a r r i e r ; and b l o c k i n g a n t i b o d y r e s p o n s e s . W i t h r e s p e c t to this last topic, we shall d i s c u s s in g r e a t e r detail, r e c e n t s t u d i e s in w h i c h we have s t a r t e d to look for p o t e n t i a l b l o c k i n g a n t i b o d i e s in a m o u s e m o d e l system. A s c a l e d - d o w n v e r s i o n of the h y b r i d o m a t e c h n i q u e has b e e n u s e d as an a n a l y t i c a l p r o b e of the s p e c i f i c i t y and i s o t y p e of i m m u n o g l o b u l i n s e c r e t e d by cells o r i g i n a l l y s i t u a t e d e i t h e r c l o s e to the m i d - g e s t a t i o n m o u s e e m b r y o or in the l y m p h n o d e s (PALN) d r a i n i n g the p r e g n a n t uterus. Some monoclonal a n t i b o d i e s w i t h s p e c i f i c i t y for e m b r y o s and e x t r a - e m b r y o n i c m e m b r a n e s have b e e n derived.