i0
Immunology 7))@ voI. 3, No. I 1982
antibodies directed against different determinants located on the H-2K k molecule 6. Competitive antibody binding studies using these monoclonals have placed the determinants in two, spatially separate, polymorphic domains of the molecule, A and B. These monoclonal antibodies were used to block target antigen recognition for both allogeneic a n d anti-trinitrophenyl H-2K k restricted C T L 7. It was found that, although antibodies directed to both cluster A a n d B reduce C T L activity, monoclonal antibodies to cluster B are m u c h more effective in target-cell protection, suggesting that a larger proportion of alloreactive and H-2 restricted T cells react with the determinants of cluster B. Inhibition of C T L by anti-H-2K monoclonal antibodies demonstrated that each individual monoclonal blocks a fraction of the C T L effector population while a mixture of monoclonals or a polyvalent antisera prevents lysis almost completely. It is clear that the determinants recognized by H-2 restricted C T L are not the same determinants seen by the monoclonal antibodies. T h e specificities of the monoclonal antibodies have been shown to define 'public' epitopes on the H-2 molecule. If such serologically defined public specificities were involved in H-2 restriction, then H-2 restriction, by definition, could not exist. Several interesting points are suggested from these findings. It is possible that both alloreactive as well as H-2 restricted populations are capable of recognizing identical epitopes on a given M H C encoded molecule. If this is the case, T cells of the species may use a similar pool of V genes to recognize the same determinant as an allo-antigen or a
self-restricting element. We must also consider the possibility that there may be multiple restricting elements for each M H C locus. If so, do these determinants define a family of allele-specific 'private' H-2 specificities? O r can the cross reactions seen in many experimental situations be a consequence of the fact that multiple restricting specificities are not always allele-specific? The use of such monoclonals in the purification of the epitopes recognized by T cells may help resolve some of these questions a n d allow an understanding of both the evolution of the complex as a whole and the relationship of its structure with its function in situ. J, DOUGLAS
WATERHELD
ICRF Tumour Immunology Unit, Department of Zoology, University CollegeLondon, Gower&reel, London, U. If.
References I Klein, J. (1980) in Immunology 80. Progresa in Immunology IV. (Fougereau, M. and Dausset, J. eds) pp 239 - 253, Academic Press, London 2 Orr, H. T., Lancet, D., Robb, R.J., Lopez de Castro, J. A. and Stominger, J. L. (1979) Nuture (London) 282,266-270 3 Nairn, R. Yamoga, K. and Nathenson, S. G. (1980) Ann. Rev. Genetics 14, 241-277 4 Zinkernagel, R. M. (1976)J. Exp. Med. 143,437-443 5 Strominger, J. L. (1980) in Immunology 80. Progressin Immunology IV. (Fougereau, M. and Dausset, J. eds) pp 542-554, Academic Press London 6 Lemke, H. and H~.mmerling, G. J. (1981) in Monoclonal AnIibodies and T Cell Hybridomaa (H/immerling, G. J., H~mmerling, U. and Kearney, J. F. eds) Elsevier, Amsterdam, (in press) 7 Weyland, C., H/immerling, G. J. and Goronzy, J. (1981) Nature (London) 292, 627-629
El (,..,.-. The T-cell antigen receptor" the minimal hypothesis revisited JohnJ. Marchalonis Department of Biochemistry, Medical University of South Carolina, Charleston, South Carolina 29425, U.S.A. A review in which J . j . Marehalonis discusses what has been learnt about the T-cell receplorjbr antigen through the search for immunoglobulin-related recognilion structures on antigen-specific T cells.
No issue in contemporary immunology has been fraught with more controversy t h a n the problenq of the T-cell receptor for antigen. It became clear more t h a n a decade ago that T-cells did not themselves secrete antibodies but their functional properties as helpers, suppressors, cytotoxic cells a n d effectors in delayedtype hypersensitivity established that they possessed an exquisite specificity in the recognition of antigen. Elseviel Biomcdical Prc~s 1982 0167-4919/82/00011 0{100/$2.75
T h e most obvious prediction was that their primary receptor for antigen, i.e. that surface molecule which actually b o u n d the specific ligand, would be 'antibody-like' in its combining site because it seemed unlikely that nature would have devised two complex sets of proteins to recognize the same sets of foreign molecules ~. This n o t i o n - the ' m i n i m a l h y p o t h e s i s ' had Occam's razor edge of simplicity a n d could
ImmunologyTo@ vol. 3, JVb. 1 1982 be directly tested by determining whether immunoglobulin (Ig)-related determinants were associated with the membrane of T-lymphocytes and whether antisera directed against such determinants would interfere with antigen-specific T-cell recognition. Although a wealth of affirmative answers were obtained to both of these questions 2, conflicting interpretations soon arose because other workers did not detect T-cell Ig-related molecules using ostensibly similar approaches 3, and T-cells were found to bind lg passively 2. In addition, the profound effects of the major histocompatibility complex on the capacity of various animals to elaborate specific immune responses was recognized, and the proposition that the M H C , particularly the /-region, encoded T-cell receptors tor antigen was strongly advocated 4. Three major lines of approach were taken to resolve the problem of the T-cell receptor for antigen. One approach which followed from the original statement of the minimal hypothesis was to seek Ig-related recognition structures on antigen-specific T-cells. The second approach was to determine the role of M H C encoded structures in antigen-specific T-cell function. The third approach was the detection of antigenspecific T-cell derived molecules based solely on their capacity to bind antigen. In this brief review, I shall focus upon the Ig-related T-cell receptor but will build upon all three avenues of approach to develop a consistent picture of antigen-specific T-cell receptors. A minimal description of the primary receptor for antigen on T-cells is as follows: This receptor possesses combining sites comprised of Ig variable regions but its constant regions are not necessarily identical to those of circulating antibodies. This is the obvious prediction which follows from the specificity of T-cells in the recognition of antigen coupled with the fact that T-cells carry out antigen-specific functions distinct from those of antibody molecules or B cells. Ig V regions might be expected to be involved in primary binding of antigen, which is a diffusion-controlled thermodynamic process dependent upon affinity of the receptor and not upon the M H C background of the cells 5. The minimal description is essentially no different from that of antigen receptors on B lymphocytes, namely membrane IgM and I g D . These molecules possess Ig variable region combining sites indistinguishable from those of serum antibody, but their heavy chains differ from those of their direct serum homologues because of the presence of hydrophobic tail segments which allow them to intercalate with the plasma membrane ~. They clearly express g or 8 isotypic markers, however.
Serological Support for the minimal hypothesis The T-cell case is rather murky historically because most of the antisera strictly specific for ~, ~. or g or other heavy chain isotypic determinants usually did not react with T-cell surface molecules using any of the techniques described. However, a number of antisera which were apparently strictly specific for Igs did
react with the T-cell surface and allowed the isolation of moleculesT,L Early studies showed that the Igrelated surface molecule of T-cells bound antigen ~ but differed from surface Ig molecules of B cells in functional properties 9, although a misconception lingers that the Ig-related T-cell product was claimed to be '8S IgM'. Following the tenets of the minimal hypothesis, one would expect that antisera made against the combining site portion of antibody molecules might react with T-cell receptors although those specific for constant region determinants would probably not react. This occurred in practice. Ramseier and his colleagues first obtained evidence for the presence of determinants related to the idiotypes of combining site determinants of Ig molecules on functionally specific T lymphocytestL The existence of surface molecules bearing idiotype-related determinants was clearly established by Binz and Wigzelp2; Rajewsky and Eichmann 13 and numerous others have now obtained evidence supporting that conclusionl
Immunology 7))@ voI. 3, No. I 1982
antibodies directed against different determinants located on the H-2K k molecule 6. Competitive antibody binding studies using these monoclonals have placed the determinants in two, spatially separate, polymorphic domains of the molecule, A and B. These monoclonal antibodies were used to block target antigen recognition for both allogeneic a n d anti-trinitrophenyl H-2K k restricted C T L 7. It was found that, although antibodies directed to both cluster A a n d B reduce C T L activity, monoclonal antibodies to cluster B are m u c h more effective in target-cell protection, suggesting that a larger proportion of alloreactive and H-2 restricted T cells react with the determinants of cluster B. Inhibition of C T L by anti-H-2K monoclonal antibodies demonstrated that each individual monoclonal blocks a fraction of the C T L effector population while a mixture of monoclonals or a polyvalent antisera prevents lysis almost completely. It is clear that the determinants recognized by H-2 restricted C T L are not the same determinants seen by the monoclonal antibodies. T h e specificities of the monoclonal antibodies have been shown to define 'public' epitopes on the H-2 molecule. If such serologically defined public specificities were involved in H-2 restriction, then H-2 restriction, by definition, could not exist. Several interesting points are suggested from these findings. It is possible that both alloreactive as well as H-2 restricted populations are capable of recognizing identical epitopes on a given M H C encoded molecule. If this is the case, T cells of the species may use a similar pool of V genes to recognize the same determinant as an allo-antigen or a
self-restricting element. We must also consider the possibility that there may be multiple restricting elements for each M H C locus. If so, do these determinants define a family of allele-specific 'private' H-2 specificities? O r can the cross reactions seen in many experimental situations be a consequence of the fact that multiple restricting specificities are not always allele-specific? The use of such monoclonals in the purification of the epitopes recognized by T cells may help resolve some of these questions a n d allow an understanding of both the evolution of the complex as a whole and the relationship of its structure with its function in situ. J, DOUGLAS
WATERHELD
ICRF Tumour Immunology Unit, Department of Zoology, University CollegeLondon, Gower&reel, London, U. If.
References I Klein, J. (1980) in Immunology 80. Progresa in Immunology IV. (Fougereau, M. and Dausset, J. eds) pp 239 - 253, Academic Press, London 2 Orr, H. T., Lancet, D., Robb, R.J., Lopez de Castro, J. A. and Stominger, J. L. (1979) Nuture (London) 282,266-270 3 Nairn, R. Yamoga, K. and Nathenson, S. G. (1980) Ann. Rev. Genetics 14, 241-277 4 Zinkernagel, R. M. (1976)J. Exp. Med. 143,437-443 5 Strominger, J. L. (1980) in Immunology 80. Progressin Immunology IV. (Fougereau, M. and Dausset, J. eds) pp 542-554, Academic Press London 6 Lemke, H. and H~.mmerling, G. J. (1981) in Monoclonal AnIibodies and T Cell Hybridomaa (H/immerling, G. J., H~mmerling, U. and Kearney, J. F. eds) Elsevier, Amsterdam, (in press) 7 Weyland, C., H/immerling, G. J. and Goronzy, J. (1981) Nature (London) 292, 627-629
El (,..,.-. The T-cell antigen receptor" the minimal hypothesis revisited JohnJ. Marchalonis Department of Biochemistry, Medical University of South Carolina, Charleston, South Carolina 29425, U.S.A. A review in which J . j . Marehalonis discusses what has been learnt about the T-cell receplorjbr antigen through the search for immunoglobulin-related recognilion structures on antigen-specific T cells.
No issue in contemporary immunology has been fraught with more controversy t h a n the problenq of the T-cell receptor for antigen. It became clear more t h a n a decade ago that T-cells did not themselves secrete antibodies but their functional properties as helpers, suppressors, cytotoxic cells a n d effectors in delayedtype hypersensitivity established that they possessed an exquisite specificity in the recognition of antigen. Elseviel Biomcdical Prc~s 1982 0167-4919/82/00011 0{100/$2.75
T h e most obvious prediction was that their primary receptor for antigen, i.e. that surface molecule which actually b o u n d the specific ligand, would be 'antibody-like' in its combining site because it seemed unlikely that nature would have devised two complex sets of proteins to recognize the same sets of foreign molecules ~. This n o t i o n - the ' m i n i m a l h y p o t h e s i s ' had Occam's razor edge of simplicity a n d could
ImmunologyTo@ vol. 3, JVb. 1 1982 be directly tested by determining whether immunoglobulin (Ig)-related determinants were associated with the membrane of T-lymphocytes and whether antisera directed against such determinants would interfere with antigen-specific T-cell recognition. Although a wealth of affirmative answers were obtained to both of these questions 2, conflicting interpretations soon arose because other workers did not detect T-cell Ig-related molecules using ostensibly similar approaches 3, and T-cells were found to bind lg passively 2. In addition, the profound effects of the major histocompatibility complex on the capacity of various animals to elaborate specific immune responses was recognized, and the proposition that the M H C , particularly the /-region, encoded T-cell receptors tor antigen was strongly advocated 4. Three major lines of approach were taken to resolve the problem of the T-cell receptor for antigen. One approach which followed from the original statement of the minimal hypothesis was to seek Ig-related recognition structures on antigen-specific T-cells. The second approach was to determine the role of M H C encoded structures in antigen-specific T-cell function. The third approach was the detection of antigenspecific T-cell derived molecules based solely on their capacity to bind antigen. In this brief review, I shall focus upon the Ig-related T-cell receptor but will build upon all three avenues of approach to develop a consistent picture of antigen-specific T-cell receptors. A minimal description of the primary receptor for antigen on T-cells is as follows: This receptor possesses combining sites comprised of Ig variable regions but its constant regions are not necessarily identical to those of circulating antibodies. This is the obvious prediction which follows from the specificity of T-cells in the recognition of antigen coupled with the fact that T-cells carry out antigen-specific functions distinct from those of antibody molecules or B cells. Ig V regions might be expected to be involved in primary binding of antigen, which is a diffusion-controlled thermodynamic process dependent upon affinity of the receptor and not upon the M H C background of the cells 5. The minimal description is essentially no different from that of antigen receptors on B lymphocytes, namely membrane IgM and I g D . These molecules possess Ig variable region combining sites indistinguishable from those of serum antibody, but their heavy chains differ from those of their direct serum homologues because of the presence of hydrophobic tail segments which allow them to intercalate with the plasma membrane ~. They clearly express g or 8 isotypic markers, however.
Serological Support for the minimal hypothesis The T-cell case is rather murky historically because most of the antisera strictly specific for ~, ~. or g or other heavy chain isotypic determinants usually did not react with T-cell surface molecules using any of the techniques described. However, a number of antisera which were apparently strictly specific for Igs did
react with the T-cell surface and allowed the isolation of moleculesT,L Early studies showed that the Igrelated surface molecule of T-cells bound antigen ~ but differed from surface Ig molecules of B cells in functional properties 9, although a misconception lingers that the Ig-related T-cell product was claimed to be '8S IgM'. Following the tenets of the minimal hypothesis, one would expect that antisera made against the combining site portion of antibody molecules might react with T-cell receptors although those specific for constant region determinants would probably not react. This occurred in practice. Ramseier and his colleagues first obtained evidence for the presence of determinants related to the idiotypes of combining site determinants of Ig molecules on functionally specific T lymphocytestL The existence of surface molecules bearing idiotype-related determinants was clearly established by Binz and Wigzelp2; Rajewsky and Eichmann 13 and numerous others have now obtained evidence supporting that conclusionl
