Immunolog.y Today, vof .~, ]Vb. 2, 1982
31
[~I~(r.,trUR~ ~
The expression of Ir genes
Zollar~ ,N}lg7 and,Tar~ K/eir~ recer~t(y arg, ued ~trorzgIy (Immunology Today, 2, 22(~) z/2al imm~me re.~JJorlse(lr) gerle.s are e.vpre.rsed in T cell.r, rm! in macr@hages as proposed in the 'delermir~ant seleclion' @poghe.~is on lfle ba.d.~ (![ e.rperime~lls @ A. S. Rosen/hal, E. M . Skevach and olhe~:s, ttere,,first Etha~t Sha)ac/7 arid lhe~l Ala~l Rorer~l/m[ reply lo ,/Va.,~yarid Klein.
Is determinant selection dead? Ethan Shevach Laboratory of Immunology, National Institute of Allergy arid Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20205. Preface In lrrlmlmo/ow Today (2,228) Zoltan Nagy and J a n Klein presented strong evidence for the T-cell expression of Ir gone function. Surprising as it may seem their viewpoint is not new and the issues they discuss have frequently been debated by those of us working in the field (albeit privately and not in print, where the macrophage expression of lr gene function has been vigorously touted). Since these issues were often discussed by Alan Rosenthal and myself when we occupied laboratories at opposite ends of the elevcnth floor of the Clinical Center at National Institutes of Health, I have taken the liberty of recreating a typical discussion of the Nagy and Klein experiments. I caution readers that I have written both parts of the scenario and leave to their imagination the noise level and arm shaking that takes place during the discussion. I also apologize to Alan Rosenthal lot setting him up as the 'straw man'. T h e Scene Midway in the eleventh floor corridor, Building 10, National Institutes of llealth. l';l/talt: Alan[ Nagy and Klein really did in your determ i n a n t selection model in their Immtmolog.v Today polemic. Alat~: Wait a minute. They alsn frequently mention you in their article: surely you believe in the macrophage expression of lr gene function? t'~/l~at~: First, let's set the record straight. In our original manuscript' describing the failure of the nonresponder macrophage to [)resent antigen to the (nonresponder x responder)F~ T cell, we actually proposed that nonresponder macrophages 'activate F / cells poorly becausc the recognition sites for the antigen are physically related to the macrophagc-binding site of the responder parent while the main contacts between the (:ells are at the non-responder binding sitcs'. Basically, a complicated model of T-cell expression of Ir gene function based on the idea that the Ir genes coded for the T-cell receptor. If you remember correctly, we were afraid to suggest the simpler explanation of a defect in macrophage presentation controlled by the Ir genes.
A/aTe: You were quick to j u m p on the macrophage b a n d w a g o n when it started rolling. /';/hare: True enough, but in the back of my mind I never forgot the T-cell models and in fact none of the experiments done to date, even your own in the insulin system, really ruled out the T-cell expression of Ir gene function. Ala~z: Do you believe the Nagy a n d Klein studies? Elhar~: 1 think they are 100% right. Robert Clark and I have been conducting studies precisely along the sam(: lines and have reached the same conclusions e. We set out to generate T-cell colonies from responder strain 2 guinea pigs which would be specific for the polymer GL in association with non-responder strain 13 macrophages. Of course, in order to get around the M H C restriction for self seen in priming studies i~l ~,ir~J we carried out all the priming in z,itr~. W e c o u l d easily separate the completely alloreactive T cells from the antigen-specific T cells by cloning the population in soft agar after priming in liquid cultures. Identification of colonies specific for nonresponder la and GL was facilitated by splitting each colony into two liquid cultures immediately after they had been picked from the agar and then examining the resultant colonies for differcntiaI growth in the presence of (;L. We easily identilied a n u m b e r of T-cell colonies of responder strain 2 origin which were totally free of alloreactivity and which proliferated spccitically only when challenged with G L in the presence of allogeneic, nonrcspondcr strain 13 macrophages. Ala~: Interesting. W h a t do you conclude? IQhael: O u r conclusions are identical lo those o! Nagy and Klein. blacrophages from the nonresponder are fully capable of presenting G L to a responder T-cell population and there is no limitation in the macrophage processing, surface display, or association of (;L with non-responder strain 13 la antigens. A/a,/: Sounds
pretty heretical coming from your
nlonth, but data is data. Wait! t low do you know that
lmmundogj Today, vof 3, .Nb. 2, lg82
32 the strain 2 colonies that respond to 13-Gl~ are not very rare clones specific tbr a minor determinant on the copolymer which is also immunogenic in strain 13 animals but is not seen in the intact animal because too few clones are involved to generate a response. P2ha*l: That's a rcasonable objection that I cannot fully answer. First, we have been unable to generate clones i*l vilro from strain 13 cells which respond to 13G L , but a negative result is difficult to interpret in these kinds of studies. What you really are asking is how frequent in the responder T-cell population are precursors for T cells that respond to 13-GL, compared with T cells that respond to 2-GL? These studies are in progress and I am willing to speculate from some of our data that we arc not dealing with a rare T-cell clone in our studies. You don't look convinced. A/m~: What would you predict about the outcome of similar studies with insulins where the specific determinant recognized by the T cell can be precisely defined? ~ l';ltla~: George Dos Reis and 1 have already initiated studies in your model system 4. The only change from our previous protocol is that we first diminished the number of alloreactive T ceils by a preculture with macrnphages in the absence of antigen followed by exposure to BUdR and light; the resultant f cells were thcn primed with beef insulin and then cloned on soft agar. Several strain 13 cohmies were identified which proliferated when challenged with beef insulin in the presence of allogeneic strain 2 peritoneal exudate cells (PEC), but not syngeneic strain 13 PEC. Analysis of the reactivity of such T-cell colonies to a series of insulins demonstrated that they reacted equally well to beef, sheep and pork insulin, thus localizing the stimulatory determinant to the insulin g chain. Your own studies demonstrated that strain 2 animals do not respond to insulin B chain, yet our data clearly indicate that non-respondcr strain 2 macrophages present B chain to responder strain 13 T cells. Studies with purified B chain and its fragments are in progress and we are also in the process of generating T-cell clones of strain 2 origin which should be specific for the insulin A chain a-loop in association with strain 13 macrnphages. Here again, the strain 13 macrophage should be fully capable of presenting the a-loop to a strain 2 T cell even though lhe strain 13 'F cell cannot be sensitized to a-lnop in association with 13 Ia antigens. Alarl: Pretty impressive if you can pull it off. What are you going to call the theory? Anti-I)elerminant Selection?
combination o[ determinants of conventional antigen and cell surface Ia while in other cases non-responsiveness is secondary to a hole in the T-cell repertnire? F.t/mH: I'll stick my neck out and state that almost all cases of/-region controlled non-responsiveness will be secondary to holes in the T-cell repertoire - the two best studied guinea pig models (poly-i.-lysine and insulin) seem to follow this pattern. Alam How is the hole in the repertoire created? t'~l/zam: l think Ron Schwartz was right when he suggested the 'clonal deletion model '5. As applied to my studies, thc failure of the strain 13 guinea pig to respond to GL is secondary to the fact that the complex of GL and strain 13 Ia mimics the complex of strain 13 Ia and some unknown self-antigen; the clone capable of seeing such a complex is deleted during Tcell ontogeny in the bone marrow or thymus. A/cm: So you really think determinant selection is dead and we should all abandon our studies on the macrophage expression of Ir gene action. El/mr~: There is one theoretical question left which suggests that the concept of determinant selection has at least a few last gasps. Let us assume a single T-ceil receptor with binding sites for both conventibnal antigen and Ia antigens. In my view, the conventional antigen and la are maintained as distinct entities and are then brought together by the T-cell receptor to form a tripartite receptor-immunogen complex. However, the possibility must still be left open that some interaction of conventional antigen and Ia might occur which is independent of that mediated by the T-ceil receptor, or that there is an interaction of conventional antigen and la within the receptor-immunogen complex which is independent of the affinity of the receptor for both the conventional antigen and for In. ,'l/rm: Well, it was a good hypothesis when I first considered it. E/hem: I would be the first to agree. T. H. Huxley's remarks about hypotheses can easily be applied to the concept of determinant selection and lr gene expression at the level of the macrophage: ' . . . the scientific hypothesis [has a value] proportionate to the care and completeness with which its basis has been tested and vcritied. It is in these matters as in the commonest affairs of practical life: the guess of the fool will be folly, while the guess of the wise man will contain wisdom. In all cases, you see that the value of the resuh depends on the patiencc and faithfulness with which the investigator applies to his hypothesis every kind of verificat ion. '"
P2haa: Not a bad idea.
A/a~: Seriously, could you adopt a middle ground position and say that in certain cases macrophages may dictate lr gene eontrol by allowing a restricted
References 1 Shevach, E. M and Rosenthal, A. S. (1973),7. l~p..tied. 138, 1215
33
lmtmmology Today, vol. .3, . Vo. 2, 1~)82
2 Glark, R. B. and Shevach, E. M. (1982).7. £"q~. Med. (in press) 3 Rosenthal, A. S., Barcinski, M. A. and Blake, ,j. T. (1977) .'v)d~tre 267, 156 4 Dos Reis, G. A. and Shevach, E. M. (1982) (in preparation)
5 Schwartz, R. I1. (1978)&-a~d7. lmmt+t~J/. 7, 3 6 Huxley, T. ft. 'We are all Scientists' in The .\}'~ 7 re(t~,(~ q/ 3'~ie~e, edited by Shapley, H., Rappaport, S. and Wright, H. Harper & Row, New York, p. 12
Determinant selection and macrophage function A. S. Rosenthal Merck Sharp and l)ohmc Research Laboratories, Rahway, New Jersey 07065, U.S.A. T h e arguments of Nagy a n d Klein conccrning the determinant selection hypothesis ~ are seriously flawed by failurc to distinguish between (1) the specificity of the T-cell receptor(s); (2) the nature of the antigenic signal(s); and (3) the means by which gene products of the M H C restrict the cellular interaction dependent process ofT-cell activation. To be use.ful, any model of the immune response ( l r ) gene p h e n o m e n o n must reconcile certain facts. First, successful T-cell activation requires at least two and perhaps more cooperative cellular events in which an antigen-presenting cell or macrophage must bear both products of the I region and nominal antigens, in order that a proliferative response be induced in a second, specific, receptor-bearing 'F cell. These cell interactions are inhibited by antibody directed against the I region but are not inhibited by antibody against antigen 2. Such data raise important but unanswered questions. First, why do T cells apparently respond to amino acid sequence variation in proteins rather t h a n to conformational alterations in protein structure? Second, is the la determinant the much sought after ~Ir gene' product? Third, is the failure of macrophages of nonresponder origin to present a consequence of defective antigen or antigen fragment interaction with available self restriction elements, i.e. Ia determinants, or do genetic or somatic holes exist in the T-cell repertoire? If somatic in origin, do they arise as a result of mimicry of self antigens? The concept of d e t e r m i n a n t selection at its simplest dcfines thc role of the macrophage in antigen recognilion by T lymphocytes. It states that the T-cell repertoire is a function of the association of restricted molecular domains of the nominal protein antigen with I region gene products. It is clear even in early studies fi'om my laboratory by Greineder e! al. ~ that 'non-antigenic' forms of macrophage-dependent Tcell activation also require the participation of the I region, in that both allogcneic alone and sodiumperiodatc-treated allogeneic macrophages were effective slimulators of T lymphocyte proliferation. These observations, and more findings that monoclonal antila sera which inhibit the responses to one antigen but not the response to another antigen under the control of the same I region j, suggest strongly that the restriction element in m a c r n p h a g e - T interaction is an
independent function of the / region - probably a domain conserved throughout the species and distinct from that associated with the fragments of, or selected regions of, the nominal antigen. In addition, Lin e! a/. ~ in studies of the intra-l-region [1-2 I, mutant, B.6C bml2, find that lr-gene function is identical with the antigen associative function of la. Central to thc challenge of Nagy and Klein is their critique of our interpretation of F~ (responder by nonresponder) type experiments as support tor the determinant selection concept. They fail to recognize that even Shevach and I interpreted the original F~ studies in 1973 "`7 in favor of a "['-cell model'; we did so betbre the response to antigens of restricted heterogeneity, such as insulin, provided an alternative interpretation giving a major role to the macrophage. We now recognizc that in a responder by non-responder F I animal, d e t e r m i n a n t selection can occur" either d u r i n g ontogeny, such that a given antigenic domain in association with the non-responder allelic product is deleted because it mimics an undefined sell'antigen, or during priming where certain antigenic domains associate only with the responder la allelic product. Either variant of the determinant selection hypothesis thus requires both Ia and an antigen to create an appropriate antigenic signal for the T cell and is not defined by the time in the life of the animal in which it operates. Indeed the concept of a 'hole' in the T repertoire as proposed by Schwartz s is and remains consistent with the critical role of the macrophage in antigen recognition since, as stated above, it only moves the time of selection fi'om maturity to that period in the development of immunocnmpetence when self and not self are discriminated. In this latter" form of determinant selection, absence of diminished responsiveness in the mature animal is not a consequence of failure in association between an antigen sequence and the non-responder la but occurs as the result of a successful association, albeit one in which self mimicry requires deletion of responsiveness. Arguments to refute or support any model of T-cell antigen recognition cannot be based upon positively or negatively selected clones of responder origin if the antigens used lack defined determinants as do glutamic acid-alanine or glutamic acid-lysine random copolymers').uk Responsiveness of such selected ~al6 v 4910/82/~u{*~a
~luuq~/S2-:,
31
[~I~(r.,trUR~ ~
The expression of Ir genes
Zollar~ ,N}lg7 and,Tar~ K/eir~ recer~t(y arg, ued ~trorzgIy (Immunology Today, 2, 22(~) z/2al imm~me re.~JJorlse(lr) gerle.s are e.vpre.rsed in T cell.r, rm! in macr@hages as proposed in the 'delermir~ant seleclion' @poghe.~is on lfle ba.d.~ (![ e.rperime~lls @ A. S. Rosen/hal, E. M . Skevach and olhe~:s, ttere,,first Etha~t Sha)ac/7 arid lhe~l Ala~l Rorer~l/m[ reply lo ,/Va.,~yarid Klein.
Is determinant selection dead? Ethan Shevach Laboratory of Immunology, National Institute of Allergy arid Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20205. Preface In lrrlmlmo/ow Today (2,228) Zoltan Nagy and J a n Klein presented strong evidence for the T-cell expression of Ir gone function. Surprising as it may seem their viewpoint is not new and the issues they discuss have frequently been debated by those of us working in the field (albeit privately and not in print, where the macrophage expression of lr gene function has been vigorously touted). Since these issues were often discussed by Alan Rosenthal and myself when we occupied laboratories at opposite ends of the elevcnth floor of the Clinical Center at National Institutes of Health, I have taken the liberty of recreating a typical discussion of the Nagy and Klein experiments. I caution readers that I have written both parts of the scenario and leave to their imagination the noise level and arm shaking that takes place during the discussion. I also apologize to Alan Rosenthal lot setting him up as the 'straw man'. T h e Scene Midway in the eleventh floor corridor, Building 10, National Institutes of llealth. l';l/talt: Alan[ Nagy and Klein really did in your determ i n a n t selection model in their Immtmolog.v Today polemic. Alat~: Wait a minute. They alsn frequently mention you in their article: surely you believe in the macrophage expression of lr gene function? t'~/l~at~: First, let's set the record straight. In our original manuscript' describing the failure of the nonresponder macrophage to [)resent antigen to the (nonresponder x responder)F~ T cell, we actually proposed that nonresponder macrophages 'activate F / cells poorly becausc the recognition sites for the antigen are physically related to the macrophagc-binding site of the responder parent while the main contacts between the (:ells are at the non-responder binding sitcs'. Basically, a complicated model of T-cell expression of Ir gene function based on the idea that the Ir genes coded for the T-cell receptor. If you remember correctly, we were afraid to suggest the simpler explanation of a defect in macrophage presentation controlled by the Ir genes.
A/aTe: You were quick to j u m p on the macrophage b a n d w a g o n when it started rolling. /';/hare: True enough, but in the back of my mind I never forgot the T-cell models and in fact none of the experiments done to date, even your own in the insulin system, really ruled out the T-cell expression of Ir gene function. Ala~z: Do you believe the Nagy a n d Klein studies? Elhar~: 1 think they are 100% right. Robert Clark and I have been conducting studies precisely along the sam(: lines and have reached the same conclusions e. We set out to generate T-cell colonies from responder strain 2 guinea pigs which would be specific for the polymer GL in association with non-responder strain 13 macrophages. Of course, in order to get around the M H C restriction for self seen in priming studies i~l ~,ir~J we carried out all the priming in z,itr~. W e c o u l d easily separate the completely alloreactive T cells from the antigen-specific T cells by cloning the population in soft agar after priming in liquid cultures. Identification of colonies specific for nonresponder la and GL was facilitated by splitting each colony into two liquid cultures immediately after they had been picked from the agar and then examining the resultant colonies for differcntiaI growth in the presence of (;L. We easily identilied a n u m b e r of T-cell colonies of responder strain 2 origin which were totally free of alloreactivity and which proliferated spccitically only when challenged with G L in the presence of allogeneic, nonrcspondcr strain 13 macrophages. Ala~: Interesting. W h a t do you conclude? IQhael: O u r conclusions are identical lo those o! Nagy and Klein. blacrophages from the nonresponder are fully capable of presenting G L to a responder T-cell population and there is no limitation in the macrophage processing, surface display, or association of (;L with non-responder strain 13 la antigens. A/a,/: Sounds
pretty heretical coming from your
nlonth, but data is data. Wait! t low do you know that
lmmundogj Today, vof 3, .Nb. 2, lg82
32 the strain 2 colonies that respond to 13-Gl~ are not very rare clones specific tbr a minor determinant on the copolymer which is also immunogenic in strain 13 animals but is not seen in the intact animal because too few clones are involved to generate a response. P2ha*l: That's a rcasonable objection that I cannot fully answer. First, we have been unable to generate clones i*l vilro from strain 13 cells which respond to 13G L , but a negative result is difficult to interpret in these kinds of studies. What you really are asking is how frequent in the responder T-cell population are precursors for T cells that respond to 13-GL, compared with T cells that respond to 2-GL? These studies are in progress and I am willing to speculate from some of our data that we arc not dealing with a rare T-cell clone in our studies. You don't look convinced. A/m~: What would you predict about the outcome of similar studies with insulins where the specific determinant recognized by the T cell can be precisely defined? ~ l';ltla~: George Dos Reis and 1 have already initiated studies in your model system 4. The only change from our previous protocol is that we first diminished the number of alloreactive T ceils by a preculture with macrnphages in the absence of antigen followed by exposure to BUdR and light; the resultant f cells were thcn primed with beef insulin and then cloned on soft agar. Several strain 13 cohmies were identified which proliferated when challenged with beef insulin in the presence of allogeneic strain 2 peritoneal exudate cells (PEC), but not syngeneic strain 13 PEC. Analysis of the reactivity of such T-cell colonies to a series of insulins demonstrated that they reacted equally well to beef, sheep and pork insulin, thus localizing the stimulatory determinant to the insulin g chain. Your own studies demonstrated that strain 2 animals do not respond to insulin B chain, yet our data clearly indicate that non-respondcr strain 2 macrophages present B chain to responder strain 13 T cells. Studies with purified B chain and its fragments are in progress and we are also in the process of generating T-cell clones of strain 2 origin which should be specific for the insulin A chain a-loop in association with strain 13 macrnphages. Here again, the strain 13 macrophage should be fully capable of presenting the a-loop to a strain 2 T cell even though lhe strain 13 'F cell cannot be sensitized to a-lnop in association with 13 Ia antigens. Alarl: Pretty impressive if you can pull it off. What are you going to call the theory? Anti-I)elerminant Selection?
combination o[ determinants of conventional antigen and cell surface Ia while in other cases non-responsiveness is secondary to a hole in the T-cell repertnire? F.t/mH: I'll stick my neck out and state that almost all cases of/-region controlled non-responsiveness will be secondary to holes in the T-cell repertoire - the two best studied guinea pig models (poly-i.-lysine and insulin) seem to follow this pattern. Alam How is the hole in the repertoire created? t'~l/zam: l think Ron Schwartz was right when he suggested the 'clonal deletion model '5. As applied to my studies, thc failure of the strain 13 guinea pig to respond to GL is secondary to the fact that the complex of GL and strain 13 Ia mimics the complex of strain 13 Ia and some unknown self-antigen; the clone capable of seeing such a complex is deleted during Tcell ontogeny in the bone marrow or thymus. A/cm: So you really think determinant selection is dead and we should all abandon our studies on the macrophage expression of Ir gene action. El/mr~: There is one theoretical question left which suggests that the concept of determinant selection has at least a few last gasps. Let us assume a single T-ceil receptor with binding sites for both conventibnal antigen and Ia antigens. In my view, the conventional antigen and la are maintained as distinct entities and are then brought together by the T-cell receptor to form a tripartite receptor-immunogen complex. However, the possibility must still be left open that some interaction of conventional antigen and Ia might occur which is independent of that mediated by the T-ceil receptor, or that there is an interaction of conventional antigen and la within the receptor-immunogen complex which is independent of the affinity of the receptor for both the conventional antigen and for In. ,'l/rm: Well, it was a good hypothesis when I first considered it. E/hem: I would be the first to agree. T. H. Huxley's remarks about hypotheses can easily be applied to the concept of determinant selection and lr gene expression at the level of the macrophage: ' . . . the scientific hypothesis [has a value] proportionate to the care and completeness with which its basis has been tested and vcritied. It is in these matters as in the commonest affairs of practical life: the guess of the fool will be folly, while the guess of the wise man will contain wisdom. In all cases, you see that the value of the resuh depends on the patiencc and faithfulness with which the investigator applies to his hypothesis every kind of verificat ion. '"
P2haa: Not a bad idea.
A/a~: Seriously, could you adopt a middle ground position and say that in certain cases macrophages may dictate lr gene eontrol by allowing a restricted
References 1 Shevach, E. M and Rosenthal, A. S. (1973),7. l~p..tied. 138, 1215
33
lmtmmology Today, vol. .3, . Vo. 2, 1~)82
2 Glark, R. B. and Shevach, E. M. (1982).7. £"q~. Med. (in press) 3 Rosenthal, A. S., Barcinski, M. A. and Blake, ,j. T. (1977) .'v)d~tre 267, 156 4 Dos Reis, G. A. and Shevach, E. M. (1982) (in preparation)
5 Schwartz, R. I1. (1978)&-a~d7. lmmt+t~J/. 7, 3 6 Huxley, T. ft. 'We are all Scientists' in The .\}'~ 7 re(t~,(~ q/ 3'~ie~e, edited by Shapley, H., Rappaport, S. and Wright, H. Harper & Row, New York, p. 12
Determinant selection and macrophage function A. S. Rosenthal Merck Sharp and l)ohmc Research Laboratories, Rahway, New Jersey 07065, U.S.A. T h e arguments of Nagy a n d Klein conccrning the determinant selection hypothesis ~ are seriously flawed by failurc to distinguish between (1) the specificity of the T-cell receptor(s); (2) the nature of the antigenic signal(s); and (3) the means by which gene products of the M H C restrict the cellular interaction dependent process ofT-cell activation. To be use.ful, any model of the immune response ( l r ) gene p h e n o m e n o n must reconcile certain facts. First, successful T-cell activation requires at least two and perhaps more cooperative cellular events in which an antigen-presenting cell or macrophage must bear both products of the I region and nominal antigens, in order that a proliferative response be induced in a second, specific, receptor-bearing 'F cell. These cell interactions are inhibited by antibody directed against the I region but are not inhibited by antibody against antigen 2. Such data raise important but unanswered questions. First, why do T cells apparently respond to amino acid sequence variation in proteins rather t h a n to conformational alterations in protein structure? Second, is the la determinant the much sought after ~Ir gene' product? Third, is the failure of macrophages of nonresponder origin to present a consequence of defective antigen or antigen fragment interaction with available self restriction elements, i.e. Ia determinants, or do genetic or somatic holes exist in the T-cell repertoire? If somatic in origin, do they arise as a result of mimicry of self antigens? The concept of d e t e r m i n a n t selection at its simplest dcfines thc role of the macrophage in antigen recognilion by T lymphocytes. It states that the T-cell repertoire is a function of the association of restricted molecular domains of the nominal protein antigen with I region gene products. It is clear even in early studies fi'om my laboratory by Greineder e! al. ~ that 'non-antigenic' forms of macrophage-dependent Tcell activation also require the participation of the I region, in that both allogcneic alone and sodiumperiodatc-treated allogeneic macrophages were effective slimulators of T lymphocyte proliferation. These observations, and more findings that monoclonal antila sera which inhibit the responses to one antigen but not the response to another antigen under the control of the same I region j, suggest strongly that the restriction element in m a c r n p h a g e - T interaction is an
independent function of the / region - probably a domain conserved throughout the species and distinct from that associated with the fragments of, or selected regions of, the nominal antigen. In addition, Lin e! a/. ~ in studies of the intra-l-region [1-2 I, mutant, B.6C bml2, find that lr-gene function is identical with the antigen associative function of la. Central to thc challenge of Nagy and Klein is their critique of our interpretation of F~ (responder by nonresponder) type experiments as support tor the determinant selection concept. They fail to recognize that even Shevach and I interpreted the original F~ studies in 1973 "`7 in favor of a "['-cell model'; we did so betbre the response to antigens of restricted heterogeneity, such as insulin, provided an alternative interpretation giving a major role to the macrophage. We now recognizc that in a responder by non-responder F I animal, d e t e r m i n a n t selection can occur" either d u r i n g ontogeny, such that a given antigenic domain in association with the non-responder allelic product is deleted because it mimics an undefined sell'antigen, or during priming where certain antigenic domains associate only with the responder la allelic product. Either variant of the determinant selection hypothesis thus requires both Ia and an antigen to create an appropriate antigenic signal for the T cell and is not defined by the time in the life of the animal in which it operates. Indeed the concept of a 'hole' in the T repertoire as proposed by Schwartz s is and remains consistent with the critical role of the macrophage in antigen recognition since, as stated above, it only moves the time of selection fi'om maturity to that period in the development of immunocnmpetence when self and not self are discriminated. In this latter" form of determinant selection, absence of diminished responsiveness in the mature animal is not a consequence of failure in association between an antigen sequence and the non-responder la but occurs as the result of a successful association, albeit one in which self mimicry requires deletion of responsiveness. Arguments to refute or support any model of T-cell antigen recognition cannot be based upon positively or negatively selected clones of responder origin if the antigens used lack defined determinants as do glutamic acid-alanine or glutamic acid-lysine random copolymers').uk Responsiveness of such selected ~al6 v 4910/82/~u{*~a
~luuq~/S2-:,
