TRENDS
Intestinal gluten sensitivity: snapshots of an unusual autoimmune-like disease Cliona O'Farrelly and Richard B. Gallagher
Intestinal gluten sensitivity, classically known as coeliac disease, is defined and diagnosed on the basis of the small intestinal response to the dietary wheat protein, gluten. The active lesion, visualized by routine histological analysis of small intestinal biopsies, is characterized by villous atrophy, epithelial cell disarray, crypt hyperplasia and lymphocytic infiltrate of the epithelium and the lamina propria. These changes all resolve to a greater or lesser extent in patients on a gluten-free diet. There is little evidence of direct gluten-mediated toxicity and the lesion is generally considered to be the result of immunologically-mediated effector mechanisms. Indeed, intestinal gluten sensitivity has all the hallmarks of autoimmune disease. First, it is strongly associated with a major histocompatibility complex (MHC) gene product, HLA-DQ2, which is in linkage disequilibrium with A1, B8 and D R w l 7 , the 'autoimmune' haplotype. Second, the primary site of disease is a hotbed of immunological activity, characterized by a massive lymphocytic infiltrate. Third, an autoantibody (against endomyceum) appears to be specific for the disease. Fourth, it is more common in females than in males and fifth, it responds to treatment with corticosteroids. However, intestinal gluten sensitivity is unique among autoimmune-type disorders in that the causative agent, gluten, is known. Thus it is often suggested, rather glibly, that the disease is a result of a breakdown of oral tolerance to dietary gluten in genetically susceptible individuals. Tolerance and tolerance breakdown
The cellular and molecular interactions required for the generation,
Gluten-sensitive disease is activated in genetically susceptible individuals by the ingestion of wheat protein (gluten). Breakdown in normal tolerogenic processes to dietary gluten is likely to play a primary pathogenic role. The disease is characterized by several autoimmune-type features and provides a model for studying autoimmune processes. A recent meeting* emphasized the need for a clearer picture of the molecular interactions between disease triggering agents, molecules of the immune system and other products of disease susceptibility genes.
resolved, although absence of costimulatory molecules normally required for T-cell activation may be important in the generation of tolerance2. Quantitative changes in the binding of antigen by MHC class II molecules also appear to influence the nature of the T-cell responseS; thus, changes in MHC class II molecule expression by coeliac epithelial cells (L. Madrigal, Dublin) may be relevant to tolerance breakdown. Differential expression of other adhesion molecules and cytokine elaboration by the enterocytes are likely to play a role in immunohomeostasis at the gut-lumen interface by influencing maintenance and breakage of the homing and regulation of lymimmunological tolerance are only phocyte subpopulations. now being defined. Several factors The phenotype, cytokine profile influence the development of regu- and function of the responding cells latory T-cell subsets in the gastroin- themselves is also crucial to testinal tract, including the nature whether or not tolerance ensues. of the antigen, the antigen concen- Several novel subpopulations of T tration, the site of antigen cells have recently been identified encounter, the characteristics of the in the small intestine (P. antigen-presenting cells and of the Brandtzaeg, Oslo; S. Lynch, responding T cells. Dublin) although few functional From the early assumption that analyses have yet been performed. all ingested protein was digested in There is strong evidence that T-cell the lumen, it is now known that receptor ~ + intraepithelial lymdietary protein is found in the cir- phocytes (IELs) mature in the gut culation minutes after ingestion. without thymic influences: message This gut-processed antigen is for recombination activation gene 1 tolerogenic when compared with (RAG-l) has been demonstrated in native or systemically-processed murine gut4; CD4*CD8 ÷ double antigen (R. Truncone, Naples). positive IELs have been demonRecent experiments have shown strated in the human (S. Lynch, that enterocytes can process and Dublin) and mouse small intestine s, present antigen to T cells in a fash- and tissue-specific deletion has ion which differs from classical been observed in mice (L. antigen processing and pres- Lefrancois, Farmington). IELs that entation1; the molecular nature of express CD80t0t homodimers but these differences needs to be n o t CD80t~ heterodimers have also been shown to be thymoindependent and to differentiate in the gut *The International Coeliac Symposium (D. Guy-Grand, Paris) 6. How the was held in Dublin, Ireland on 22-25 gut epithelium influences T-cell July 1992. maturation, whether these cells © 1992, Elsevier Science Publishers Ltd, UK.
ImmunologyToday
474
Vot 13No.21992
TRENDS
undergo antigen-specific tolerance induction and whether changes in these processes might play a role in gluten-sensitive disease are crucial questions. Understanding the role of TCR ~'8+ cells in health and disease will also depend on resolving these issues. It has been hypothesized that this is a primitive population of cells which acts as a primary line of &fence, and that it has a limited repertoire of specificities, perhaps reacting against some product of altered or stressed self cells 7. TCR 7& cells in mice display a distinctive anatomical distribution (A. Hayday, New Haven). A significant proportion of them respond to heat shock protein ~ and their maturation is unaffected in TCRix~ knockout mice ~. There is controversy about the restriction element for 78T cells, although CD1 (which is expressed on mouse epithelium) can act as a ligand t° and there is evidence that 78 T cells that express neither CD4 nor CD8 (a subpopulation which is increased in coeliac disease; S. Lynch, Dublin) abrogate oral tolerance t ~. Despite the interest in these cells, the increase in 78 Tcell numbers in gluten intestinal sensitivity and other diseases of the gastrointestinal tract has no known pathogenic significance.
Gluten research A crucial component of gluten intestinal sensitivity, is, of course, wheat protein. Studies on the specific influences of this dietary constituent on enterocyte and IEL maturation and function in normal and diseased small intestine have been hampered by its chemical nature. It has complex solubility and adhesive properties which are ideal for bread-making but difficult for science. Analyses of toxicity and immunogenicity are also complicated by the fact that, as wheat protein is a storage rather than functional protein, multiple mutations have occurred and been maintained; thus, gluten is not a single protein, but a myriad of closely related entities (H. Weiser, Garching). The homologous storage proteins of closely related graminae, rye and barley are also toxic to gluten sensitive patients.
Some progress has been made in identifying the toxic moieties of gluten (D. Kasarda, Albany). Initially using enzymatic digests, and more recently with synthetic peptides, several toxic sequences have been postulated - sequences 1-30 and 31-43 (S. Auricchio, Naples), 75-86 and 213-227 (H. Cornell, Melbourne) of A-gliadin. The first two peptides inhibit development of 17-day old rat foetal small intestine and also prevent the expected in vitro improvement of small intestinal biopsies from patients with active disease. Mannan and oligomers of Nacetylglucosamine prevent the toxic effect (S. Auricchio, Naples). However, a limitation to these studies has been the lack of a convincing disease specificity in this in vitro model of toxicity.
Immunologicallymediated damage There is no doubt that, in common with many infectious diseases and diseases of autoimmune origin, immunological mechanisms play a fundamental role in the generation of the characteristic damage ill gluten-sensitive disease. The lymphocytic infiltration, increased MHC class II expression, increased numbers of CD25 + T cells (P. Brandtzaeg, Oslo), subepithelial complement deposition (T. Halstensen, Oslo), enhanced expression of heat shock proteins on the surface epithelium (A. Whelan, Dublin) and evidence of macrophage and eosinophil degranulation {A. Whelan, Dublin; B. Lavo, Uppsala; T. MacDonald, London) are all markers of an angry, damaging immune response. At present, however, it is still impossible to determine whether immunological mechanisms reflect (1) a normal response to damage, (2) changes caused directly by gluten or (3) are specifically stimulated by wheat protein to initiate the pathogenic lesion. IgA anti-endomysial antibodies, which are directed against an extracellular matrix protein, appear to be exclusive to patients with active coeliac disease (A. Burgin-Wolff, Basle; C. Sategna-Guidetti, Turin; M. Farre, Barcelona; R. Willoughby, Dublin and others).
Immunology Today
475
rot.
N,,.
Together with the finding of increased levels of IgA Fc receptors in the lamina propria (A. Whelan, Dublin) and evidence of complement and eosinophil activation, this suggests that antibody-mediated mechanisms are important in the generation of the pathogenic lesion. However, the coeliac dogma has long held that the T cell plays a central role. A mononuclear inflammatory infiltrate is a fundamental characteristic of the intestinal lesion. Early experiments by MacDonald and Ferguson I, demonstrated the release of lymphocyte products from coeliac small intestinal biopsies after stimulation with wheat protein; the enhanced expression of MHC class II molecules by coeliac epithelial cells probably reflects release of gamma-interferon (IFN- 7) by activated T cells. And the recent isolation of gluten-specific HLA-DQrestricted T cells from the jejunal biopsies of gluten-sensitive patients (K. Lundin, Oslo) provides compelling new evidence for a decisive role for a T-cell response and fits beautifully with the finding that the disease is almost exclusively associated with a particular HLA-DQ heterodimer (encoded by the D Q A I * 0 5 0 3 and DQB2*0203 alleles, associated in cis or in trans; M. Kagnoff, San Diego). Evidence is also emerging that the products of activated T cells influence small intestinal structure and function. Using human foetal explants, mitogen stimulation of T cells leads to rapid mucosal destruction, with loss of villi, crypt hyperplasia and epithelial damage (T. MacDonald, London). In animal models, graft-versus-host disease has a significant gastrointestinal component, characterized by crypt cell stimulation. This is mediated by the products of CD4 + T cells which act either directly on epithelial cells or by activating other non-specific inflammatory cells (A. Mowat, Glasgow). Supernatants from activated T cells increase the number of epithelial cells entering 'S' phase m vitro (J. McDevitt, Dublin), while T-cell products, including IFN-¥, tumour necrosis factor (TNF) and interleukin 6 (IL-6) interfere with the
,')92
TRENDS
build up a picture of which events are of pathogenic significance. This is important not only from the point of view of understanding the autoimmune process, but also because in some patients intestinal gluten sensitivity appears to be a pre-malignant condition enteropathy-associated T-cell lymphoma is an unusually common complication in this subgroup 14. Again this is an area of controversy as, on the one hand, it is argued that the malignancy arises because of chronic stimulation in the gastrointestinal tract (Howdle, Leeds) while, on the other hand, it is possible that the conditions which allow the emergence of a sub-population of T cells responsible for breakdown in tolerance to gliadin may also interfere with more fundamental growth and differentiation patterns. There is a basic problem with work in this field, which is characteristic of all research into human autoimmune mechanisms. A series of pictures is built up, some of which are quite complex and even complete in themselves. But it is impossible, without a significant amoun't of imagination (or Guinness) to link together these static pictures into a dynamic representation of how genetic predisposition, together with specific initiating events, lead to activation of effector mechanisms responsible for pathogenesis. How are we ever
structure and function of epithelial cell tight junctions 13. Epilogue The changes in lymphocyte subpopulations, cytokine profiles, surface marker expression and uptake of ingested protein that are seen in the coeliac small intestinal mucosa may fundamentally influence the pathogenic process. Alternatively, they may merely reflect chronic pathogenic mechanisms which continue long after important initiating events have taken place. Thus, the analysis of active, classic coeliac mucosa is unlikely to help differentiate between effector and initiating events. It is now clear that a milder intestinal lesion is found in patients who have latent coeliac disease (Arranz, Edinburgh), in first degree relatives of coeliac patients (M. Marsh, Leeds) and in patients whose primary site of manifestation of gluten sensitivity is not the gut but the skin (in dermatitis herpetiformis; S. O ' M a h o n y , Edinburgh). In each of these groups, the gross small intestinal histology appears normal. However, more detailed analysis reveals the IEL infiltrate and secretory immune response, with raised levels of gliadin specific IgA and IgM typical of classic intestinal gluten-sensitivity. Because fewer mechanisms have been activated in these situations, it may be easier to
Genome
Mapping
and
going to make a movie from the stills? Cliona O'Farrelly is at the Dept of I m m u n o l o g y , Trinity College, Dublin, Ireland and Richard Gallagher is the editor of Immunology Today.
References 1 Bland, P. and Warren, L.G. (1986) Immunology 58, 1-7 2 Weaver, C.T. and Unanue, E.R. (1990) lmmunol. Today 11, 49-55 3 Bottomly, K. (1991) Immunol. Today 12, 346-348 4 Rocha, B., Vassalli, P. and GuyGrand, D. (1991) J. Exp. Med. 173, 483-486 5 Mosley, R.L., Styre, D. and Klein, J.R. (1990) Int. Immunol. 2, 361-365 6 Rocha B., Vassalli, P. and GuyGrand, D. (1992) Immunol. Today 13, 7 Janeway, C.A. (1988) Nature 333, 804-806 8 Born, H., Hall, L. and Dallas, A. et al. (1990) Science 249, 66-69 9 Philpott, K.C., Viney, J.L., Kat, G. et al. (1992) Science 256, 1448-1452 10 Balk, S.P., Ebert, E.C., Blumenthal, R.L. et al. (1990) Science 253, 1411-1414 11 Fujihashi, K., Taguchi, T., McGhee, J.R. et al. (1990) J. Immunol. 145, 2010-2019 12 Ferguson, A., McClure, J.P., MacDonald, T.T. and Holden, R.J. (1975) Lancet i, 895-897 13 Madara, J.L. and Stafford, J. (1989) J. Clin. Invest. 83,724-727 14 McCarthy, C.F. (1991) Eur. J. Gastroenterol. Hepatol. 3, 125-128
Sequencing
A Special Issue from Trends in Biotechnology ITs companion journal, TIBTECH, has produced a special issue covering many aspects of genome mapping and sequencing. The methodology required for large-scale genome analysis is constantly evolving, necessitating innovative technologies and adaptations/automation of existing molecular biology techniques. These methods and approaches to the handling of the enormous volumes of data being produced are considered, as are organizational and financial aspects of the projects.
Topics covered include: • Targeted genome analysis- cDNA cloning • Laser microdissection and microcloning • Flow cytometry sequencing technology • Advanced cloning vectors • Model genomes
•
In situ hybridization and structural analysis in relation to function and mapping
• •
Database organization and co-ordination of international data networks Artificialintelligence and sequence feature recognition International perspectives on project structuring
•
Contributing authors include: R. Anand, M. Bevan, A.J. Brookes, G.N. Cameron, C.R. Cantor, H. Cooke, C. Fields, K.O. Greulich, J.D. Harding, L. Hood, J.R. Korenberg, P. Little, E. Magnien, D. Porteous, A. Rosenthal, E.C. Uberbacher, M. Uhldn, A. Vassarotti and J.C. Venter. Copies of this special issue (for UK£8.50/US$15.00) may be ordered from: Trends in Biotechnology, Elsevier Trends Journals, 68 Hills Road, Cambridge, UK CB2 1LA
Immunology Today
476
rot. 13 No. 12 1992
Intestinal gluten sensitivity: snapshots of an unusual autoimmune-like disease Cliona O'Farrelly and Richard B. Gallagher
Intestinal gluten sensitivity, classically known as coeliac disease, is defined and diagnosed on the basis of the small intestinal response to the dietary wheat protein, gluten. The active lesion, visualized by routine histological analysis of small intestinal biopsies, is characterized by villous atrophy, epithelial cell disarray, crypt hyperplasia and lymphocytic infiltrate of the epithelium and the lamina propria. These changes all resolve to a greater or lesser extent in patients on a gluten-free diet. There is little evidence of direct gluten-mediated toxicity and the lesion is generally considered to be the result of immunologically-mediated effector mechanisms. Indeed, intestinal gluten sensitivity has all the hallmarks of autoimmune disease. First, it is strongly associated with a major histocompatibility complex (MHC) gene product, HLA-DQ2, which is in linkage disequilibrium with A1, B8 and D R w l 7 , the 'autoimmune' haplotype. Second, the primary site of disease is a hotbed of immunological activity, characterized by a massive lymphocytic infiltrate. Third, an autoantibody (against endomyceum) appears to be specific for the disease. Fourth, it is more common in females than in males and fifth, it responds to treatment with corticosteroids. However, intestinal gluten sensitivity is unique among autoimmune-type disorders in that the causative agent, gluten, is known. Thus it is often suggested, rather glibly, that the disease is a result of a breakdown of oral tolerance to dietary gluten in genetically susceptible individuals. Tolerance and tolerance breakdown
The cellular and molecular interactions required for the generation,
Gluten-sensitive disease is activated in genetically susceptible individuals by the ingestion of wheat protein (gluten). Breakdown in normal tolerogenic processes to dietary gluten is likely to play a primary pathogenic role. The disease is characterized by several autoimmune-type features and provides a model for studying autoimmune processes. A recent meeting* emphasized the need for a clearer picture of the molecular interactions between disease triggering agents, molecules of the immune system and other products of disease susceptibility genes.
resolved, although absence of costimulatory molecules normally required for T-cell activation may be important in the generation of tolerance2. Quantitative changes in the binding of antigen by MHC class II molecules also appear to influence the nature of the T-cell responseS; thus, changes in MHC class II molecule expression by coeliac epithelial cells (L. Madrigal, Dublin) may be relevant to tolerance breakdown. Differential expression of other adhesion molecules and cytokine elaboration by the enterocytes are likely to play a role in immunohomeostasis at the gut-lumen interface by influencing maintenance and breakage of the homing and regulation of lymimmunological tolerance are only phocyte subpopulations. now being defined. Several factors The phenotype, cytokine profile influence the development of regu- and function of the responding cells latory T-cell subsets in the gastroin- themselves is also crucial to testinal tract, including the nature whether or not tolerance ensues. of the antigen, the antigen concen- Several novel subpopulations of T tration, the site of antigen cells have recently been identified encounter, the characteristics of the in the small intestine (P. antigen-presenting cells and of the Brandtzaeg, Oslo; S. Lynch, responding T cells. Dublin) although few functional From the early assumption that analyses have yet been performed. all ingested protein was digested in There is strong evidence that T-cell the lumen, it is now known that receptor ~ + intraepithelial lymdietary protein is found in the cir- phocytes (IELs) mature in the gut culation minutes after ingestion. without thymic influences: message This gut-processed antigen is for recombination activation gene 1 tolerogenic when compared with (RAG-l) has been demonstrated in native or systemically-processed murine gut4; CD4*CD8 ÷ double antigen (R. Truncone, Naples). positive IELs have been demonRecent experiments have shown strated in the human (S. Lynch, that enterocytes can process and Dublin) and mouse small intestine s, present antigen to T cells in a fash- and tissue-specific deletion has ion which differs from classical been observed in mice (L. antigen processing and pres- Lefrancois, Farmington). IELs that entation1; the molecular nature of express CD80t0t homodimers but these differences needs to be n o t CD80t~ heterodimers have also been shown to be thymoindependent and to differentiate in the gut *The International Coeliac Symposium (D. Guy-Grand, Paris) 6. How the was held in Dublin, Ireland on 22-25 gut epithelium influences T-cell July 1992. maturation, whether these cells © 1992, Elsevier Science Publishers Ltd, UK.
ImmunologyToday
474
Vot 13No.21992
TRENDS
undergo antigen-specific tolerance induction and whether changes in these processes might play a role in gluten-sensitive disease are crucial questions. Understanding the role of TCR ~'8+ cells in health and disease will also depend on resolving these issues. It has been hypothesized that this is a primitive population of cells which acts as a primary line of &fence, and that it has a limited repertoire of specificities, perhaps reacting against some product of altered or stressed self cells 7. TCR 7& cells in mice display a distinctive anatomical distribution (A. Hayday, New Haven). A significant proportion of them respond to heat shock protein ~ and their maturation is unaffected in TCRix~ knockout mice ~. There is controversy about the restriction element for 78T cells, although CD1 (which is expressed on mouse epithelium) can act as a ligand t° and there is evidence that 78 T cells that express neither CD4 nor CD8 (a subpopulation which is increased in coeliac disease; S. Lynch, Dublin) abrogate oral tolerance t ~. Despite the interest in these cells, the increase in 78 Tcell numbers in gluten intestinal sensitivity and other diseases of the gastrointestinal tract has no known pathogenic significance.
Gluten research A crucial component of gluten intestinal sensitivity, is, of course, wheat protein. Studies on the specific influences of this dietary constituent on enterocyte and IEL maturation and function in normal and diseased small intestine have been hampered by its chemical nature. It has complex solubility and adhesive properties which are ideal for bread-making but difficult for science. Analyses of toxicity and immunogenicity are also complicated by the fact that, as wheat protein is a storage rather than functional protein, multiple mutations have occurred and been maintained; thus, gluten is not a single protein, but a myriad of closely related entities (H. Weiser, Garching). The homologous storage proteins of closely related graminae, rye and barley are also toxic to gluten sensitive patients.
Some progress has been made in identifying the toxic moieties of gluten (D. Kasarda, Albany). Initially using enzymatic digests, and more recently with synthetic peptides, several toxic sequences have been postulated - sequences 1-30 and 31-43 (S. Auricchio, Naples), 75-86 and 213-227 (H. Cornell, Melbourne) of A-gliadin. The first two peptides inhibit development of 17-day old rat foetal small intestine and also prevent the expected in vitro improvement of small intestinal biopsies from patients with active disease. Mannan and oligomers of Nacetylglucosamine prevent the toxic effect (S. Auricchio, Naples). However, a limitation to these studies has been the lack of a convincing disease specificity in this in vitro model of toxicity.
Immunologicallymediated damage There is no doubt that, in common with many infectious diseases and diseases of autoimmune origin, immunological mechanisms play a fundamental role in the generation of the characteristic damage ill gluten-sensitive disease. The lymphocytic infiltration, increased MHC class II expression, increased numbers of CD25 + T cells (P. Brandtzaeg, Oslo), subepithelial complement deposition (T. Halstensen, Oslo), enhanced expression of heat shock proteins on the surface epithelium (A. Whelan, Dublin) and evidence of macrophage and eosinophil degranulation {A. Whelan, Dublin; B. Lavo, Uppsala; T. MacDonald, London) are all markers of an angry, damaging immune response. At present, however, it is still impossible to determine whether immunological mechanisms reflect (1) a normal response to damage, (2) changes caused directly by gluten or (3) are specifically stimulated by wheat protein to initiate the pathogenic lesion. IgA anti-endomysial antibodies, which are directed against an extracellular matrix protein, appear to be exclusive to patients with active coeliac disease (A. Burgin-Wolff, Basle; C. Sategna-Guidetti, Turin; M. Farre, Barcelona; R. Willoughby, Dublin and others).
Immunology Today
475
rot.
N,,.
Together with the finding of increased levels of IgA Fc receptors in the lamina propria (A. Whelan, Dublin) and evidence of complement and eosinophil activation, this suggests that antibody-mediated mechanisms are important in the generation of the pathogenic lesion. However, the coeliac dogma has long held that the T cell plays a central role. A mononuclear inflammatory infiltrate is a fundamental characteristic of the intestinal lesion. Early experiments by MacDonald and Ferguson I, demonstrated the release of lymphocyte products from coeliac small intestinal biopsies after stimulation with wheat protein; the enhanced expression of MHC class II molecules by coeliac epithelial cells probably reflects release of gamma-interferon (IFN- 7) by activated T cells. And the recent isolation of gluten-specific HLA-DQrestricted T cells from the jejunal biopsies of gluten-sensitive patients (K. Lundin, Oslo) provides compelling new evidence for a decisive role for a T-cell response and fits beautifully with the finding that the disease is almost exclusively associated with a particular HLA-DQ heterodimer (encoded by the D Q A I * 0 5 0 3 and DQB2*0203 alleles, associated in cis or in trans; M. Kagnoff, San Diego). Evidence is also emerging that the products of activated T cells influence small intestinal structure and function. Using human foetal explants, mitogen stimulation of T cells leads to rapid mucosal destruction, with loss of villi, crypt hyperplasia and epithelial damage (T. MacDonald, London). In animal models, graft-versus-host disease has a significant gastrointestinal component, characterized by crypt cell stimulation. This is mediated by the products of CD4 + T cells which act either directly on epithelial cells or by activating other non-specific inflammatory cells (A. Mowat, Glasgow). Supernatants from activated T cells increase the number of epithelial cells entering 'S' phase m vitro (J. McDevitt, Dublin), while T-cell products, including IFN-¥, tumour necrosis factor (TNF) and interleukin 6 (IL-6) interfere with the
,')92
TRENDS
build up a picture of which events are of pathogenic significance. This is important not only from the point of view of understanding the autoimmune process, but also because in some patients intestinal gluten sensitivity appears to be a pre-malignant condition enteropathy-associated T-cell lymphoma is an unusually common complication in this subgroup 14. Again this is an area of controversy as, on the one hand, it is argued that the malignancy arises because of chronic stimulation in the gastrointestinal tract (Howdle, Leeds) while, on the other hand, it is possible that the conditions which allow the emergence of a sub-population of T cells responsible for breakdown in tolerance to gliadin may also interfere with more fundamental growth and differentiation patterns. There is a basic problem with work in this field, which is characteristic of all research into human autoimmune mechanisms. A series of pictures is built up, some of which are quite complex and even complete in themselves. But it is impossible, without a significant amoun't of imagination (or Guinness) to link together these static pictures into a dynamic representation of how genetic predisposition, together with specific initiating events, lead to activation of effector mechanisms responsible for pathogenesis. How are we ever
structure and function of epithelial cell tight junctions 13. Epilogue The changes in lymphocyte subpopulations, cytokine profiles, surface marker expression and uptake of ingested protein that are seen in the coeliac small intestinal mucosa may fundamentally influence the pathogenic process. Alternatively, they may merely reflect chronic pathogenic mechanisms which continue long after important initiating events have taken place. Thus, the analysis of active, classic coeliac mucosa is unlikely to help differentiate between effector and initiating events. It is now clear that a milder intestinal lesion is found in patients who have latent coeliac disease (Arranz, Edinburgh), in first degree relatives of coeliac patients (M. Marsh, Leeds) and in patients whose primary site of manifestation of gluten sensitivity is not the gut but the skin (in dermatitis herpetiformis; S. O ' M a h o n y , Edinburgh). In each of these groups, the gross small intestinal histology appears normal. However, more detailed analysis reveals the IEL infiltrate and secretory immune response, with raised levels of gliadin specific IgA and IgM typical of classic intestinal gluten-sensitivity. Because fewer mechanisms have been activated in these situations, it may be easier to
Genome
Mapping
and
going to make a movie from the stills? Cliona O'Farrelly is at the Dept of I m m u n o l o g y , Trinity College, Dublin, Ireland and Richard Gallagher is the editor of Immunology Today.
References 1 Bland, P. and Warren, L.G. (1986) Immunology 58, 1-7 2 Weaver, C.T. and Unanue, E.R. (1990) lmmunol. Today 11, 49-55 3 Bottomly, K. (1991) Immunol. Today 12, 346-348 4 Rocha, B., Vassalli, P. and GuyGrand, D. (1991) J. Exp. Med. 173, 483-486 5 Mosley, R.L., Styre, D. and Klein, J.R. (1990) Int. Immunol. 2, 361-365 6 Rocha B., Vassalli, P. and GuyGrand, D. (1992) Immunol. Today 13, 7 Janeway, C.A. (1988) Nature 333, 804-806 8 Born, H., Hall, L. and Dallas, A. et al. (1990) Science 249, 66-69 9 Philpott, K.C., Viney, J.L., Kat, G. et al. (1992) Science 256, 1448-1452 10 Balk, S.P., Ebert, E.C., Blumenthal, R.L. et al. (1990) Science 253, 1411-1414 11 Fujihashi, K., Taguchi, T., McGhee, J.R. et al. (1990) J. Immunol. 145, 2010-2019 12 Ferguson, A., McClure, J.P., MacDonald, T.T. and Holden, R.J. (1975) Lancet i, 895-897 13 Madara, J.L. and Stafford, J. (1989) J. Clin. Invest. 83,724-727 14 McCarthy, C.F. (1991) Eur. J. Gastroenterol. Hepatol. 3, 125-128
Sequencing
A Special Issue from Trends in Biotechnology ITs companion journal, TIBTECH, has produced a special issue covering many aspects of genome mapping and sequencing. The methodology required for large-scale genome analysis is constantly evolving, necessitating innovative technologies and adaptations/automation of existing molecular biology techniques. These methods and approaches to the handling of the enormous volumes of data being produced are considered, as are organizational and financial aspects of the projects.
Topics covered include: • Targeted genome analysis- cDNA cloning • Laser microdissection and microcloning • Flow cytometry sequencing technology • Advanced cloning vectors • Model genomes
•
In situ hybridization and structural analysis in relation to function and mapping
• •
Database organization and co-ordination of international data networks Artificialintelligence and sequence feature recognition International perspectives on project structuring
•
Contributing authors include: R. Anand, M. Bevan, A.J. Brookes, G.N. Cameron, C.R. Cantor, H. Cooke, C. Fields, K.O. Greulich, J.D. Harding, L. Hood, J.R. Korenberg, P. Little, E. Magnien, D. Porteous, A. Rosenthal, E.C. Uberbacher, M. Uhldn, A. Vassarotti and J.C. Venter. Copies of this special issue (for UK£8.50/US$15.00) may be ordered from: Trends in Biotechnology, Elsevier Trends Journals, 68 Hills Road, Cambridge, UK CB2 1LA
Immunology Today
476
rot. 13 No. 12 1992
