Inflammation at the interface of innate and acquired immunity

This is the short summary of the presentation at the 2nd Belgrade Meeting on Immunoregulation entitled "Inflammation at the interface of Innate and Acquired Immunity" held recently under the auspice of European Federation of Immunological Societies and organized by Medical School, University of Kragujevac.

Aqueous humor alloreactive cell phenotypes, cytokines and chemokines in corneal allograft rejection

As biopsies are not taken at the time of human corneal allograft rejection, most information on the early cellular changes in rejection is from animal models. We examined the phenotype of alloreactive cells present in the human anterior chamber during corneal graft rejection by flow cytometry and quantified aqueous humor levels of cytokines and chemokines using cytometric bead array. Aqueous and peripheral blood samples were taken from patients with graft endothelial rejection (n = 11) and from control patients undergoing cataract surgery (n = 8). CD45(+)CD4(+), CD45(+)CD8(+) and CD45(+)CD14(+) cells were found in aqueous during rejection; no CD45(+) cells were seen in control samples. Higher proportions of CD45(+) cells found in aqueous during rejection were CD14(+), denoting monocyte/macrophage lineage, than were CD4(+) or CD8(+). Large elevations were seen in aqueous levels of IL-6, MCP-1 and IP-10 during rejection compared with controls; smaller but still statistically significant increases were seen in MIP-1alpha and eotaxin. The role of CD14(+) cells in allorejection is unclear as is the potential of these chemokines and their receptors as therapeutic targets. Aqueous humor samples offer a unique opportunity to analyze components of the allogeneic response in direct contact with donor tissue but without artifacts inherent in examination of tissue.

T cell recognition and interaction in the immune system

This paper discusses mechanisms of regulation within the immune system. The only cells known to be specialized for regulatory activity within this system are helper and suppressor T cells. Like other T cells, most of these cells recognize antigen only in association with products of the major histocompatibility complex. This is a mechanism which ensures that these cells function appropriately, by being activated by and exerting their effects upon their proper cellular targets. It is likely but not certain that this mechanism of dual recognition is involved in the acquisition of self tolerance, and that inappropriate associations may be a factor in the induction of autoimmunity. There is extensive but circumstantial evidence that regulatory T cells govern to a large extent not only the induction but also the course (relapse and remission) of autoimmunity. An understanding of the mechanisms involved in activating suppressor T cells is of special importance for the treatment and prevention of autoimmune disease. A variety of factors which favour activation of suppression have been identified in experimental studies. These include the nature of the antigen, the way in which it reaches the immune system, antigenic dosage, and the involvement of antigen-presenting cells. It is proposed that certain cells within the suppressor cell circuit (suppressor-effector cells) do not operate dual recognition, and that this may explain the factors which favour suppression. The high incidence of sex-linked immunodeficiency diseases is discussed. It is proposed that this can be accounted for, at least in part, by the preferential elimination of autosomal deleterious genes in the heterozygotes. This emphasizes the importance of measuring the fitness of carriers of these diseases.

A survey of H2 gene sequences, including new wild-derived genes

A comprehensive collection of mouse major histocompatibility complex (MHC) promoter and exon 2 sequences is here presented and analysed. It covers the three best known class II genes and one class I gene, and includes new wild mouse sequences from the 'w' back-cross strains and from the Jackson collection. All sequences are in GenBank, and the new exon sequences largely confirm previous typing by serology and immune function. As in human leucocyte antigen (HLA), the overall nucleotide diversity is higher in the class II genes, in keeping with their more diverse function. Diversity along the promoters is highest in the region of known transcription factor binding, most notably in and around the CRE and rCAAT sequences. This distribution parallels that of maximum single nucleotide polymorphism impact previously obtained with reporter constructs. Taking into account the low nucleotide diversity of the CIITA promoter, we conclude that MHC promoters are likely to have diversified through co-evolution with their exons, while themselves also directly subject to natural selection. The H2Eb(p) alleles form a distinct group, associated with their lack of the recombination hot spot located between exon 2 and exon 3. The collection is expected to prove useful in guiding functional and evolutionary studies.

Can unresolved infection precipitate autoimmune disease?

Autoimmune diseases are frequently postulated to arise as post-infectious phenomena. Here we survey the evidence supporting these theories, with particular emphasis on Crohn's disease and ankylosing spondylitis. Direct proof that infection establishes persistent autoimmunity remains lacking, although it may provoke a prolonged inflammatory response when occurring on a susceptible immunological background. The argument of infective causality is by no means trivial, since it carries important consequences for the safety of vaccine development.

Conditional haploinsufficiency of NCF1 (encoding p47(phox)), a signaling gene with a heterozygous phenotype potentially subject to natural selection

Even a minor degree of haploinsufficiency could eventually reduce the frequency of an autosomal immunodeficiency disease. Searching for such a condition, we have re-examined the phenotype of mice +/- for the NCF1 gene encoding p47(phox) and humans +/- for NCF1 and NCF2 using a procedure that allowed the respiratory burst of granulocytes and macrophages to be measured simultaneously. The mice showed significant haploinsufficiency in granulocytes but not in macrophages (i.e. conditional haploinsufficiency). Our human data were obtained from blister cells, and were too scattered to allow a firm conclusion. In view of recent re-evaluation of the role of the respiratory burst these findings are compatible with the view that haploinsufficiency occurs particularly among rate-limiting genes that operate in regulatory/signaling pathways.

Does the polymorphism of MHC class II promoters matter?

The promoters of genes of the major histocompatibility complex vary not only because of linkage disequilibrium with their coding sequences but also, we argue, because of natural selection that acts particularly strongly on MHC II gene promoters. Thus, the promoter of H2Eb varies more than that of H2K, to an extent that cannot be accounted for by coding variation, and the same applies to HLA.DRB1 in comparison with H2D. We discuss how transduction by lentivirus vectors followed by adoptive transfer of monoclonal T cells could be used to test the functional activity of variant mouse promoters in vivo, and how homologous recombination in suitable cell lines might provide a short cut to obtaining promoter knock-ins.

Genetic variation in the MHC II promoter: lessons for regulation and for comparative genomics

Sequence data have been accumulating that reveal variation in gene promoters of the immune system, notably in MHC class II, cytokines and chemokines. The variation is non-random: it occurs most often in proximity to and within certain regulatory elements such as CRE and NFY (in MHC class II these are respectively the X2 and Y boxes). These are elements that are widely used elsewhere in the genome, and appear to act as rheostats (modulators of expression) in contrast to the type of on-off switch operated by the RFX element that is unique to a single family of promoters such as MHC class II. It is proposed that a complex mouse phenotype described in Prague and elsewhere may reflect this pattern of variation in/around CRE. Such rheostats are expected to operate in other promoters. Their identification will be facilitated by short-range comparisons (e.g. human-chimp), and indeed this is a motive for extending comparative genomics.

The immunological synapse

The immunological synapse plays a central role in organising the immune system. Through their synaptic activity both T and B cells usually, but not always, acquire the information that critically determines the level and nature of the responses that they make. For T cells much of that information comes from epicrine and paracrine cell-cell interactions in the cluster that forms around a dendritic cell. These interactions are being dissected by experiments in which two populations of TCR-transgenic T cells are combined in vivo. Another important aspect of synaptic activity is the way in which different levels of expression of MHC class II molecules influence Th1/Th2 balance. In exploring this form of control we are learning something of general importance about cis-regulation.

Relapsing arthritis induced by cell transfer from collagen-immunised mice

Collagen-induced arthritis is a well-established model of chronic inflammatory arthritis. We here introduce a development of this model which combines the benefits of adoptive transfer and sequential relapse. DBA/1 x B10.Q F1 hybrid mice were immunised with bovine type II collagen, and those which developed a sufficiently high level of arthritis served as donors of spleen cells transferred into BALB/c SCID hosts. After boosting with 500 microg collagen, the development of host arthritis was monitored over a period of up to 256 days, during which up to three successive peaks were detected. In comparison with bovine collagen, mouse collagen used for boosting induced a lower initial peak but higher relapses. As expected, the transferred disease was more uniform than the freshly induced one. Previous information suggests that a shifting cytokine balance between protective and aggressive T cells may account for the relapse and remission. This study provides a model of relapsing polyarthritis, obtained with normal immunocytes boosted with a well-defined protein antigen in animals not themselves treated with adjuvant. As such it is relevant to the etiology of inflammatory arthritis in man, and, if further developed, could be of value for testing new therapeutic strategies.

Polymorphism in regulatory gene sequences

The extensive polymorphism revealed in non-coding gene-regulatory sequences, particularly in the immune system, suggests that this type of genetic variation is functionally and evolutionarily far more important than has been suspected, and provides a lead to new therapeutic strategies.

Self/nonself discrimination among immunoregulatory (CD4) T cells

This review covers work on immunological tolerance from 1962 up to the present, focusing on the Th, CD4+ compartment of the immune system. The principle mechanism of tolerance is identified as deletion, occurring centrally and in the periphery. In the periphery, deletion is the normal response of CD4 T cells to soluble monomeric proteins that occurs when activation (mainly of dendritic cells) is avoided. Thus activation and the signals which induce it are crucial to understanding S/NS discrimination, as has long been known. The thymus is important as the site where new T cells first see self-antigens, and as one largely shielded from activation, although deletion in the thymus and the periphery has the same threshold. The relative contribution of dendritic cells and developing T cells to deletion in the thymus remains unclear. Activation induced cell death, containment, anergy and deviation constitute subsidiary mechanisms, and sequestration/neglect is important in limiting the scope of deletion.

Interaction within clusters of dendritic cells and helper T cells during initial Th1/Th2 commitment

Cytokines are the main agents known to regulate Th1 / Th2 commitment, where they may operate through paracrine activity within clusters of T cells gathered around dendritic cells (DC). An in vitro system is used here to test this possibility, using clusters around DC composed of naive TCR-transgenic ovalbumin peptide 323 - 339-specific CD4(+) T cells as targets plus TCR-transgenic pigeon cytochrome C peptide 88 - 104-specific CD4(+) polarized Th1 or Th2 cells as inducers. The polarized inducer cells exerted their maximum effect when the two T cell populations were activated within the same cluster, implemented by allowing a single DC to present both their epitopes. This finding thus supports the paracrine hypothesis. The system was then employed to explore the role of individual cytokines by means of inhibition by monoclonal antibodies. Development of Th2 commitment proved strictly dependent on the IL-4 produced by the Th2 inducers. For Th1 commitment, IFN-gamma and IL-12 were both needed, but with IFN-gamma required only during the initial period of culture. The rapid timing observed under these conditions places constraints on the molecular basis of commitment, and appears accurately to reflect the physiological response in vivo.

Natural and induced regulation of Th1/Th2 balance

Because Th1/Th2 balance is perturbed during immunological disease, the design of strategies aiming at its rectification has become a priority. The alteration of the balance in pregnancy so as to promote survival of the fetal allograft lends credibility to this aim. Attenuation of the activation signal delivered through the T cell receptor (TCR) represents a promising approach. It is supported by the high level of polymorphism in the MHC class II promoter, which regulates the natural TCR signal and thus modulates Th1/Th2 differentiation. Further support comes from the Th2 shift that occurs in JNK knockout mice, and with kinase inhibitors and anti-CD4 monoclonal antibodies applied in vitro. The approach has implications for nasal tolerance and inhibition of IL-12 production. The further range of options for Th1/Th2 modulation, which are presented throughout this issue of the journal, are here summarised and evaluated.

Natural variation in immune responsiveness, with special reference to immunodeficiency and promoter polymorphism in class II MHC genes

This review deals with natural selection operating on heterozygotes as a key factor controlling (a) the frequency of immunodeficiencies, and (b) promoter polymorphism in MHC class II genes. The known difference in frequency distribution of X-linked and autosomal deficiencies lend support to this possibility, and suggest that the frequency of neonatal defect may rise as old-established equlibria between entry and exit of deleterious mutations change. MHC class II gene promoters differ in their capacity to favor Th1 (or reciprocally Th2) responses, thus suggesting that promoter polymorphism is sustained by the greater flexibility in response that this confers on heterozygotes.

Modulating the Th1/Th2 balance in inflammatory arthritis

The balance between Th1 and Th2 cells regulates the choice between inflammatory and antibody-mediated immune responses. To an increasing extent this balance is thought to involve the participation of antigen-presenting cells, rather than the entirely autonomous activity of T cells and their cytokines. Here we survey current opinion concerning the working of this balance, and its condition in rheumatoid arthritis and the other inflammatory arthritides. The contrast between Lyme arthritis and reactive arthritis is particularly illuminating, since one is triggered by extracellular and the other by intracellular infection. We describe current approaches to the modulation of this balance. Guided by the principles that genetic polymorphism is likely to identify relevant genes, that any cytokine gene picked up by a virus must matter and that natural immunosuppressive activity at mucosal surfaces should be worth exploiting, we identify as particularly worthy of attention: (i) IL-10, (ii) inhibitors of IL-12 production, (iii) inhibitors of CD40 ligand expression and (iv) oral and nasal tolerance. Other protective T cell subsets are touched on, and the impact of oligonucleotide arrays mentioned.

Bystander suppression of murine collagen-induced arthritis by long-term nasal administration of a self type II collagen peptide

Oral and more recently nasal tolerance have attracted attention as potential treatments of autoimmune disease. Arthritis induced by bovine type II collagen (CII) is a widely used animal model of rheumatoid arthritis, which is here used to investigate the efficacy of nasal treatment by a short peptide. The peptide spans residues 707-721 (designated p707), an epitope of mouse CII that is most strongly recognized after immunization of mice with this self-protein. The treatment was partially effective, but almost only when the peptide was administered in large doses over a prolonged period. Mice immunized with bovine CII respond mainly to other peptides, located in the CB11 fragment around amino acid residues 256-270. The tolerance effect therefore results from intramolecular suppression, between epitopes located in different parts of this large protein.

The distribution of variation in regulatory gene segments, as present in MHC class II promoters

Diversity in the antigen-binding receptors of the immune system has long been a primary interest of biologists. Recently it has been suggested that polymorphism in regulatory (noncoding) gene segments is of substantial importance as well. Here, we survey the level of variation in MHC class II gene promoters in man and mouse using extensive collections of published sequences together with unpublished sequences recently deposited by us in the EMBL gene bank using the Shannon entropy to quantify diversity. For comparison, we also apply our analysis to distantly related MHC class II promoters, as well as to class I promoters and to class II coding regions. We observe a high level of intraspecies variability, which in mouse but not in man is localized to a significant extent near the binding sites of transcription factors-sites that are conserved over longer evolutionary distances. This localization may both indicate and enhance heterozygote advantage, as the presence of two functionally different promoters would be expected to confer flexibility in the immune response.

T cell response of I-Aq mice to self type II collagen: meshing of the binding motif of the I-Aq molecule with repetitive sequences results in autoreactivity to multiple epitopes

Type II collagen (CII) is of immunological interest because of its repetitive structure and properties as an autoantigen. The mouse gene has recently been cloned, thus enabling T cell-defined epitopes to be identified. Multiple novel epitopes on mouse CII are here detected in the autoreactive T cell response. The major response is directed to an epitope with residues 707-721 located on the CB10 fragment. Some 25 other epitopes are also recognized, including the autologous homologue of the 256-270 epitope which dominates in the response to foreign collagen. The cells reactive with mouse collagen peptides were of Th1 type, as judged by release of IFN-gamma. No significant reactivity was detected to mouse CII peptides during ongoing disease. Alignment of the mouse epitopes revealed a sequence motif with characteristic side chains at residues P1, P4 and P7, and to a lesser extent at P5, within a nonamer core sequence. Binding of these epitopes was simulated in a computer model of the I-Aq molecule, where peptides with anchor residues at P1, P4 and P7 were indeed found to fit the binding groove best. The spacing of pockets and the fine structure of the binding surface of the I-Aq molecule meshes with the repetitive structure of the collagen (X-Y-Gly), thus providing a likely explanation for the occurrence of multiple epitopes. Comparison with human DR binding motifs showed that the I-Aq motif resembles most closely that of the DR4 subtypes which predispose for rheumatoid arthritis.

Thalidomide therapy of established collagen-induced arthritis (CIA) not accompanied by an evident Th2 shift

Thalidomide, a drug likely to affect the cytokine pattern, was administered orally to mice at various stages of CIA. Treatment (150 mg/kg per day by gavage, 5 days/week), started 6 weeks post-immunization, i.e. at the height of the disease, significantly reduced arthritis, and appeared also to reduce the level of inflammation as judged by neutrophil chemiluminescence. With treatment started 9 weeks post-immunization the effect on arthritis was no longer statistically significant, and when started at 14 weeks was lost. Over a dose range of up to 150 mg/kg per day the treatment had no effect on either interferon-gamma (IFN-gamma) or IL-4 mRNA levels. The treatment is therefore not likely to have operated via a shift in the Th1/Th2 balance.

Type II collagen serology: a guide to clinical responsiveness to oral tolerance?

A double-blind placebo-controlled randomized trial of oral collagen type II (CII) treatment in rheumatoid arthritis was completed in Berlin. Anti-CII antibody titres were measured before and after the treatment. They showed that: (1) the titre prior to treatment did not identify a responder subgroup, (2) the treatment reduced CII antibody titres, but only in those patients making a clinical response and (3) administration of 10 mg CII per day reduced the titre in these subsets more effectively than 1 mg per day. Although the data are limited, they suggest that a titre drop may be useful for identifying those patients who respond to this form of treatment and that the drop may be a valid parameter for detecting the impact of the treatment on the immune system.

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.

Regulation by non-major histocompatibility complex genes of the allo-4-hydroxy-phenylpyruvate dioxygenase (F liver protein) response

Although rapid progress is being made in the quantitative genetics of multifactorial disease, no response to a simple antigen has yet been subjected to full genomic analysis. The well-characterized antigen allo-HPPD (4-hydroxy-phenylpyruvate dioxygenase, previously known as F liver antigen) is a good candidate for such treatment. Old and new data bearing on this possibility are here assembled. In respect of antibody production and an early burst of interleukin-4 (IL-4) transcription, introduction of the non-major histocompatibility complex (MHC) background from A/J strain mice into F1 hybrids with C57BL10 strains up-regulates the response. These findings can be aligned with previous quantitative genetics carried out on airway hyper-responsiveness in related strains, and to a lesser extent with the genetics of autoimmune diabetes in the mouse. Taken together, the findings suggest that regulation of the pro-inflammatory cytokines are largely responsible for the variation. Additional data indicate that these non-MHC genes are are to a variable extent (depending on the response parameter) epistatic to the down-regulatory MHC allele H-2Ab.

Oral type II collagen treatment in early rheumatoid arthritis. A double-blind, placebo-controlled, randomized trial

OBJECTIVE

To investigate the efficacy of oral type II collagen in the treatment of early rheumatoid arthritis (RA).

METHODS

Ninety patients with RA (disease duration < or = 3 years) were treated for 12 weeks with oral bovine type II collagen at 1 mg/day (n = 30) or 10 mg/day (n = 30) or with placebo (n = 30), in a double-blind randomized study.

RESULTS

There were no significant difference between the 3 groups in terms of response to treatment. However, we observed a higher prevalence of responders in the type II collagen-treated groups: 7 responders in the 10-mg type II collagen group and 6 in the 1-mg group, versus 4 in the placebo group. Furthermore, 3 patients in the 10-mg type II collagen group and 1 patient in the 1-mg type II group, but no patients in the placebo group, had very good response. A total of 14 patients had to be withdrawn from the study: 2 because of side effects (nausea) and 12 because of lack of efficacy.

CONCLUSION

Only a minority of patients responded to treatment with oral type II collagen. These results justify further efforts to identify which patients will have good response to such therapy.

Variable response to a candidate cancer vaccine antigen: MHC control of the antibody response in the rat to avian erythroblastosis virus (AEV)-encoded epithelial growth factor receptor but not AEV-encoded thyroid hormones receptor

BACKGROUND

A problem likely to be encountered in any cancer immunotherapy based on vaccination with a single protein or peptide is variation in the host response. A particularly informative example is provided by the two oncogenic proteins, one intracellular and the other extracellular, encoded by the avian erythroblastosis virus (AEV), homologs of the thyroid hormones receptor (THsR) and the epithelial growth factor receptor (EGFR), respectively.

MATERIALS AND METHODS

Antibodies to these two proteins were assayed by radioimmune precipitation (RIP) in sera from MHC-congenic rats immunized by virally induced tumors.

RESULTS

Among the four haplotypes tested, RT1(1) rats exhibited a significantly lower response to the EGFR homolog than the high responders RT1c and RT1u, while RT1a rat strains had an intermediate response. Analysis of the recombinant haplotype RT1ac indicated that the response is controlled, as expected, by the class II locus of the MHC. In contrast, these rat strains responded uniformly to the intracellular THsR homolog.

CONCLUSIONS

These results support the hypothesis that MHC restriction of the response to self-related proteins reflects mainly a tolerance mechanism. They sound a note of warning for cancer vaccine development, and also one of positive advice. The likelihood of MHC restriction suggests that a widely applicable polyvalent vaccine should be the final aim in cancer immunotherapy. Yet, paradoxically, evidence of MHC restriction can help establish that a candidate vaccine is likely to prove effective.

Self-reactive T cell hybridomas and tolerance. Same range of antigen dose dependence but higher numbers of self-reactive T cell hybridomas from mice in which self-tolerance has been broken by antiserum treatment

Mechanisms of self-tolerance of 4-hydroxyphenylpyruvate dioxygenase (HPPD) are explored. It is well established that negative selection based on TCR affinity occurs in the thymus. We have investigated the frequency with which self-reactive T cell hybridomas can be obtained in relation to self-tolerance. Mice immunized with the self-form of HPPD gave rise to T cell hybridomas that were able to recognize self-protein and a synthetic peptide representing the T cell epitope, at higher Ag concentration than was necessary for recognition of allo-protein. The efficiency of negative selection was then reduced by treating neonatal mice with anti-HPPD antiserum. This reduced T cell tolerance of the self-protein, as judged by in vitro proliferation, and enabled self-reactive T cell hybridomas to be generated at a higher frequency. However, the Ag concentration requirements of these hybridomas for the self-protein and the self-peptide remained unaltered. The possibility that these findings reflect an auxiliary mechanism of self-tolerance based on frequencies of self-reactive T cells is discussed.

Self-reactive T cell hybridomas and tolerance. Same range of antigen dose dependence but higher numbers of self-reactive T cell hybridomas from mice in which self-tolerance has been broken by antiserum treatment

Mechanisms of self-tolerance of 4-hydroxyphenylpyruvate dioxygenase (HPPD) are explored. It is well established that negative selection based on TCR affinity occurs in the thymus. We have investigated the frequency with which self-reactive T cell hybridomas can be obtained in relation to self-tolerance. Mice immunized with the self-form of HPPD gave rise to T cell hybridomas that were able to recognize self-protein and a synthetic peptide representing the T cell epitope, at higher Ag concentration than was necessary for recognition of allo-protein. The efficiency of negative selection was then reduced by treating neonatal mice with anti-HPPD antiserum. This reduced T cell tolerance of the self-protein, as judged by in vitro proliferation, and enabled self-reactive T cell hybridomas to be generated at a higher frequency. However, the Ag concentration requirements of these hybridomas for the self-protein and the self-peptide remained unaltered. The possibility that these findings reflect an auxiliary mechanism of self-tolerance based on frequencies of self-reactive T cells is discussed.

Immunology of reactive arthritides

Reactive arthritis (ReA) and Lyme arthritis together comprise a pair of chronic inflammatory diseases of the joints. Although differing in detail, these relatively rare diseases are related in their immunopathology to the much commoner rheumatoid arthritis (RA), for which they serve as both model and control. The trigger for rheumatoid arthritis is unknown, but for these rarer diseases triggering occurs by certain well-defined bacterial infections. Arthritis is an uncommon outcome of these infections, for reasons unknown, and the development of chronic, as distinct from brief, arthritis is even rarer; again, the reasons are unknown. Not only does knowing the trigger greatly assist us in understanding these diseases, so also does knowing the contrasting pattern of Th1 versus Th2 cytokines observed in RA and ReA. ReA and Lyme arthritis are here considered in the wider setting of infections where chronic morbidity arises first from hypersensitivity, and perhaps finally from autoimmunity, such as occurs in some of the major tropical diseases. The immunology of ReA and Lyme disease is surveyed in detail, concentrating on T cells and including an update on the Lyme vaccine(s). Additional sections deal with the enigma of HLA B27, with epidemiological findings relevant to the chronicity of ReA and to the need for enlarged prospective studies of ReA in the setting of a developing country.

Association of H2Ab with resistance to collagen-induced arthritis in H2-recombinant mouse strains: an allele associated with reduction of several apparently unrelated responses

HLA class II alleles can protect against immunological diseases. Seeking an animal model for a naturally occurring protective allele, we screened a panel of H2-congenic and recombinant mouse strains for ability to protect against collagen-induced arthritis. The strains were crossed with the susceptible strain DBA/1, and the F1 hybrids immunized with cattle and chicken type II collagen. Hybrids having the H2Ab allele displayed a reduced incidence and duration of the disease. They also had a reduced level of pre-disease inflammation, but not of anti-collagen antibodies. The allele is already known to be associated with reduction of other apparently unrelated immune responses, suggesting that some form of functional differentiation may operate that is not exclusively related to epitope-binding. It is suggested that this may reflect allelic variation in the class II major histocompatibility complex promoter region.

Primed lymphocytes are boosted by type II collagen of their hosts after adoptive transfer

A central question in understanding autoimmunity is whether an endogenous self-antigen can drive an immune response initially triggered by a foreign one. This possibility is here tested by adoptive transfer, in which T and B cells from mice primed with foreign type II collagen were transferred into irradiated syngeneic hosts. Previous work with other protein antigens has established that primed cells normally respond only if boosted after transfer with antigen. In the present case, and in respect only to that portion of the antibody response able to bind to endogenous type II collagen, that requirement did not hold. This indicates that the anti-self component is indeed driven by endogenous antigen, which the transferred lymphocytes presumably obtain from their adoptive hosts. The transfers were carried out in C57BL10.A x DBA/1 mice using donors primed with either chick or bovine collagen, and the non-boosted responses, presumably driven by endogenous antigen, could be followed in a proportion of the recipients for as long as 45 days.

Assessment of collagen type II induced arthritis in mice by whole blood chemiluminescence

Lucigenin-enhanced chemiluminescence can be measured in 100 microliters samples of whole, unseparated mouse blood. A procedure for doing so is here described in detail, using a standard clinical luminometer. The assay measures the TPA-induced oxidative burst from granulocytes and macrophages, which is believed to depend on the overall level of inflammation in the body. It is here applied to mice suffering from type II collagen-induced arthritis, and its relation to overt disease symptoms (the arthritis score) is characterised during the course of the disease. A correlation between the assay and the arthritis score is found at the height of the disease (r = 0.42, p = .039), but not at early or very late time points, although there is a strong hint that the results of an early assay may predict the subsequent disease course. The assay provides a rapid, convenient, quantitative and economical method of assessing disease activity, which can be carried out repeatedly on the same individual. It should be applicable in other mouse models of chronic inflammatory disease. It may find application for rapid screening of novel anti-rheumatic drugs and treatments.

Where are peptides taking us in T-cell biology?

T-cell epitopes are now well understood as amino-acid nonamers binding to major histocompatibility complex molecules. Powerful methods have been developed for their identification through screening of recombinant and synthetic peptides. Multiple epitopes from a single protein are valuable for detecting T-cell reactivity in disease, currently in human immunodeficiency virus infection, and in the future in autoimmune disease. Surprises are likely to be encountered while exploring the T-cell repertoire in this way, such as positive as well as negative selection of self-reactivity. T-epitopes are likely to find important applications in therapy, particularly in down-regulation of the immune response. Multiple mechanisms of down-regulation appear to operate, among which bystander suppression by TGF beta-producing T-cells from the gut is of great current interest.

Antigen presentation, loss of immunological memory and AIDS

A key factor causing immunodeficiency in HIV infection seems to be defective antigen presentation. Consequently, CD4+ T-cell populations, initially those expressing CD45RO, decrease in number not because of their destruction, but because they fail to expand in response to antigenic stimulation. This view implies that it would be mistaken to aim therapies only at correcting T-cell function or preventing infection of T cells.

Specialization, tolerance, memory, competition, latency, and strife among T cells

Over the last four decades much insight has been gained into the working of T cells. This survey offers an interpretation of regulatory T-cell function in terms of epitope linkage and the need to free B cells of responsibility for self-tolerance. These functions dictate specialized forms of antigen presentation, by separate populations of dendritic cells. Tolerance induction among T cells occurs at a threshold of antigen concentration which is close to that required for positive stimulation, as would be expected for the efficient working of the immune system. Certain self-proteins, especially those located on cell surfaces, also induce tolerance among B cells, thus reducing the danger of activating latent epitopes. Memory among T cells is attributed to two components, one of hyperreactivity of activated cells, and the other of clonal expansion. Examples of competition and buffering between T-cell activities are given. A brief discussion of autoimmune disease focusses on the importance of disease remission, protective HLA genes, and immunoinhibitory genes in animal models. The mechanism underlying all three may be a balance between competing subsets of T cells.