Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Novel self-epitopes derived from aggrecan, fibrillin, and matrix metalloproteinase-3 drive distinct autoreactive T-cell responses in juvenile idiopathic arthritis and in health

Juvenile idiopathic arthritis (JIA) is a heterogeneous autoimmune disease characterized by chronic joint inflammation. Knowing which antigens drive the autoreactive T-cell response in JIA is crucial for the understanding of disease pathogenesis and additionally may provide targets for antigen-specific immune therapy. In this study, we tested 9 self-peptides derived from joint-related autoantigens for T-cell recognition (T-cell proliferative responses and cytokine production) in 36 JIA patients and 15 healthy controls. Positive T-cell proliferative responses (stimulation index ≥2) to one or more peptides were detected in peripheral blood mononuclear cells (PBMC) of 69% of JIA patients irrespective of major histocompatibility complex (MHC) genotype. The peptides derived from aggrecan, fibrillin, and matrix metalloproteinase (MMP)-3 yielded the highest frequency of T-cell proliferative responses in JIA patients. In both the oligoarticular and polyarticular subtypes of JIA, the aggrecan peptide induced T-cell proliferative responses that were inversely related with disease duration. The fibrillin peptide, to our knowledge, is the first identified autoantigen that is primarily recognized in polyarticular JIA patients. Finally, the epitope derived from MMP-3 elicited immune responses in both subtypes of JIA and in healthy controls. Cytokine production in short-term peptide-specific T-cell lines revealed production of interferon-γ (aggrecan/MMP-3) and interleukin (IL)-17 (aggrecan) and inhibition of IL-10 production (aggrecan). Here, we have identified a triplet of self-epitopes, each with distinct patterns of T-cell recognition in JIA patients. Additional experiments need to be performed to explore their qualities and role in disease pathogenesis in further detail.

CD134 as target for specific drug delivery to auto-aggressive CD4+ T cells in adjuvant arthritis

T cells have an important role during the development of autoimmune diseases. In adjuvant arthritis, a model for rheumatoid arthritis, we found that the percentage of CD4+ T cells expressing the activation marker CD134 (OX40 antigen) was elevated before disease onset. Moreover, these CD134+ T cells showed a specific proliferative response to the disease-associated epitope of mycobacterial heat shock protein 60, indicating that this subset contains auto-aggressive T cells. We studied the usefulness of CD134 as a molecular target for immune intervention in arthritis by using liposomes coated with a CD134-directed monoclonal antibody as a drug targeting system. Injection of anti-CD134 liposomes subcutaneously in the hind paws of pre-arthritic rats resulted in targeting of the majority of CD4+CD134+ T cells in the popliteal lymph nodes. Furthermore, we showed that anti-CD134 liposomes bound to activated T cells were not internalized. However, drug delivery by these liposomes could be established by loading anti-CD134 liposomes with the dipalmitate-derivatized cytostatic agent 5'-fluorodeoxyuridine. These liposomes specifically inhibited the proliferation of activated CD134+ T cells in vitro, and treatment with anti-CD134 liposomes containing 5'-fluorodeoxyuridine resulted in the amelioration of adjuvant arthritis. Thus, CD134 can be used as a marker for auto-aggressive CD4+ T cells early in arthritis, and specific liposomal targeting of drugs to these cells via CD134 can be employed to downregulate disease development.

Successful immunotherapy with matrix metalloproteinase-derived peptides in adjuvant arthritis depends on the timing of peptide administration

We have recently found that matrix metalloproteinases (MMPs) are targets for T-cell and B-cell reactivity in experimental arthritis. In the present article, we investigate whether modulation of MMP-specific T-cell responses could influence the course of adjuvant arthritis (AA). Lewis rats were treated nasally with MMP peptides prior to or after AA induction. Administration of the MMP-10 or the MMP-16 peptide prior to AA induction reduced the arthritic symptoms. In contrast, administration of the MMP-10 peptide after AA induction aggravated the arthritic symptoms. The present study shows the possible usefulness of MMP peptides for immunotherapy. However, a clear understanding of proper timing of peptide administration is crucial for the development of such therapies.

Immunological mechanisms involved in experimental peptide immunotherapy of T-cell-mediated diseases

Current therapies for autoimmune diseases and allergy involve general immune suppression. However, the ideal therapy should specifically eliminate or modulate the (auto)pathogenic immune response or, alternatively, it should reinforce the regulatory response, without affecting the overall function of the immune system. This could be achieved by antigen-specific immunotherapy. Antigen-specific immunotherapy has received ample attention in the last years, and several clinical trials attempting to treat autoimmune diseases or allergy through the induction of antigen-specific tolerance or immune deviation have been conducted, albeit with varying success. Recent advances in our understanding of peripheral tolerance, regulatory T cells, and routes of antigen administration have resulted in better insight into the different working mechanisms and potential target molecules of antigen-specific immunotherapy. The experimental animal models and new technological developments force the pace in the development of these immunotherapies. The current review addresses several aspects of antigen-specific immunotherapies and focuses on the mechanisms of the different approaches in experimental autoimmune and allergy models.

Structure-based design and evaluation of MHC class II binding peptides

Structural information regarding binding of peptides to the major histocompatibility complex (MHC) class II molecule is of great use for the design of compounds that intervene in the interaction between the MHC-peptide-T-cell receptor (TCR) complex. These compounds can be applied in the treatment of T-cell-mediated auto-immune disease for specific modulation of the disease process. In case no crystal structure of the MHC molecule is available, homology models of the MHC molecule can be of importance. Here we describe the construction of a homology model of the MHC class II molecule and binding of the peptide, that are involved in experimental auto-immune encephalomyelitis, a rat model for human multiple sclerosis. The validity of the model was investigated using experimental data of peptides binding to this MHC molecule.

The efficacy of immunotherapy in an experimental murine model of allergic asthma is related to the strength and site of T cell activation during immunotherapy

In the present study, the relation between the efficacy of immunotherapy, and the strength and site of T cell activation during immunotherapy was evaluated. We used a model of allergic asthma in which OVA-sensitized and OVA-challenged mice display increased airway hyperresponsiveness, airway inflammation, and Th2 cytokine production by OVA-specific T cells. In this model, different immunotherapy strategies, including different routes of administration, or treatment with entire OVA or the immunodominant T cell epitope OVA(323-339), or treatment with a peptide analogue of OVA(323-339) with altered T cell activation capacity were studied. To gain more insight in how immunotherapy affects allergen-specific T cells, the site of Ag-specific T cell activation and the magnitude of the T cell response induced during different immunotherapy strategies were determined using an adoptive transfer model. Our data suggest that amelioration of airway hyperresponsiveness and inflammation is associated with the induction of a strong, synchronized, and systemic T cell response, resulting in a decreased OVA-specific Th2 response. In contrast, deterioration of the disease after immunotherapy is associated with the induction of a weak nonsynchronized T cell response, resulting in the enhancement of the OVA-specific Th2 response after challenge.

Nasal application of a naturally processed and presented T cell epitope derived from TCR AV11 protects against adjuvant arthritis

Reactivity towards TCR peptides plays an important role in the regulation of several experimental autoimmune diseases. In a previous paper, we showed the TCRAV11 usage by an arthritogenic T cell clone isolated from a rat with adjuvant arthritis (AA). Moreover, we identified three immunogenic peptides in AV11: AV11 24-40, 41-55 and 66-80. In the present study, we show that T cells directed towards all three epitopes are part of the immune repertoire. The strongest delayed-type hypersensitivity (DTH) reaction was observed against the peptide derived from the third framework region, peptide AV11 66-80. DTH reactions to this peptide were detectable in naive rats and increased significantly after AA induction. Interestingly, modulation of the AV11 66-80 T cell response by nasal AV11 66-80 administration resulted in reduced DTH responses and in a strong inhibition of AA. These findings suggest that during the natural course of AA, T cells directed towards the third framework region of AV11 do not have a disease regulatory function, but instead play a role in the deterioration of AA.

T cell reactivity to heat shock protein 60 in diabetes-susceptible and genetically protected nonobese diabetic mice is associated with a protective cytokine profile

Spontaneous onset of pancreatic beta cell destruction in the nonobese diabetic (NOD) mouse is preceded by the induction of autoreactive T cells, which recognize a variety of autoantigens. The 60-kDa endogenous (murine) heat shock protein 60 (hsp60) has been proposed to be one of the key autoantigens. Here we demonstrate that subcutaneous immunization of normoglycemic NOD mice with highly homologous mycobacterial or murine hsp60 activates T cells in the spleen that produce high levels of IL-10 upon restimulation in vitro with either hsp60 protein. In time, increasing levels of hsp60-induced IL-10 could be detected in NOD mice, but not in age- and MHC class II-matched BiozziABH mice, which lack any sign of pancreatic inflammation. These results suggest that the IL-10 responses in NOD mice are primarily driven by endogenous inflammation. Genetically protected NOD-asp mice, showing a less progressive development of insulitis, demonstrated a similar increase in hsp60-induced IL-10 in time compared with wild-type NOD mice. Taken together, our results suggest that endogenous hsp60 is not a primary autoantigen in diabetes but is possibly associated with regulation of insulitis. Moreover, the capacity to respond to (self) hsp60 is independent of the MHC class II-associated genetic predisposition to diabetes.

Selection of T-cell epitopes from foot-and-mouth disease virus reflects the binding affinity to different cattle MHC class II molecules

The major histocompatibility complex (MHC)-restricted selection of T-cell epitopes of foot-and-mouth disease virus (FMDV) by individual cattle MHC class II DR (BoLA-DR) molecules was studied in a direct MHC-peptide binding assay. By in vitro priming of T lymphocytes derived from animals homozygous for both MHC class I and II, five T-cell epitopes were analyzed in the context of three MHC class II haplotypes. We found that the presentation of these T-cell epitopes was mediated by DR molecules, since blocking this pathway of antigen presentation using monoclonal antibody TH14B completely abolished the proliferative responses against the peptides. To study the DR-restricted presentation of these T-cell epitopes, a direct MHC-peptide binding assay on isolated cattle DR molecules was developed. Purified cattle MHC class II DR molecules of the BoLA-DRB3*0201, BoLA-DRB3*1101, and BoLA-DRB3*1201 alleles were isolated from peripheral blood mononuclear cells. For each allele, one of the identified T-cell epitopes was biotinylated, and used as a marker peptide for the development of a competitive MHC-peptide binding assay. Subsequently, the T-cell epitopes of FMDV with functionally defined MHC class II specificity were analyzed in this binding assay. The affinity of the epitopes to bind to certain DR molecules was significantly correlated to the capacity to induce T-cell proliferation. This demonstrated at the molecular level that the selection of individual T-cell epitopes found at the functional level was indeed the result of MHC restriction.

Anergic T cells as active regulators of the immune response

T cell anergy is one of the mechanisms leading to the establishment and maintenance of peripheral tolerance. Recent data from our and other laboratories indicate that anergic T cells are not functionally inert but in fact are capable of regulating the immune response in an active manner. In this review, we describe our viewpoint on how anergic self-reactive T cells could contribute to regulation of the immune response.

'Anergic' T cells modulate the T-cell activating capacity of antigen-presenting cells

Nowadays there is compelling evidence for immunoregulation by T cells. Recently, we showed that so-called 'anergic' T cells are not functionally inert but can act as regulatory cells by actively suppressing other T cell responses. We now show that 'anergic' T cells mediate this suppressive effect via modulation of the T-cell activating capacity of the antigen-presenting cell (APC). Upon removal of the 'anergic' T cells, the suppressive APC phenotype persisted, indicating that 'anergic' T cells conditioned the APC to become a mediator of T cell suppression. The inhibitory signal delivered by 'anergic' T cells depended on the presence of the cognate ligand for the 'anergic' T cell, and appeared to be dominant since previously activated APC were rendered inhibitory as well. These findings imply that APC upon cross-talk with T cells can adopt distinct functional phenotypes ranging from T-cell stimulatory to T-cell suppressive. The contribution of 'anergic' T cells to the functional tuning of APC offers an explanation for the maintenance of 'anergic' T cells in the repertoire, and for their role in immunoregulation.

Induction of T cell anergy by liposomes with incorporated major histocompatibility complex (MHC) II/peptide complexes

PURPOSE

The aim of this study was to use small unilamellar liposomes with incorporated MHC II/peptide complexes as a carrier system for multivalent antigen presentation to CD4 + T cells.

METHODS

Purified peptide pre-loaded MHC II molecules were incorporated into small unilamellar liposomes and tested for their ability to activate A2b T cells. The outcome of T cell activation by such liposomes in the absence of accessory cells was tested via flow cytometry and a T cell anergy assay.

RESULTS

Provided the presence of external co-stimulation, MHC II/ peptide liposomes were able to induce proliferation of the A2b T cell clone. More importantly incubation of these T cells with MHC II/ peptide liposomes in the absence of co-stimulation did not induce proliferation, however, a MHC/peptide ligand-density dependent down-regulation of the TCR was observed. Interestingly, when T cells after incubation with the MHC II/peptide liposomes were restimulated with their specific antigen in the presence of professional APC, these cells were anergic.

CONCLUSIONS

We propose MHC II/peptide liposomes as a novel means to induce T cell anergy. The possibility to prepare 'tailor-made' liposomal formulations may provide liposomes with an important advantage for applications in immunotherapy.

Modulation of Th2 responses by peptide analogues in a murine model of allergic asthma: amelioration or deterioration of the disease process depends on the Th1 or Th2 skewing characteristics of the therapeutic peptide

Allergen-specific CD4+ Th2 cells play an important role in the immunological processes of allergic asthma. Previously we have shown that, by using the immunodominant epitope OVA323-339, peptide immunotherapy in a murine model of OVA induced allergic asthma, stimulated OVA-specific Th2 cells, and deteriorated airway hyperresponsiveness and eosinophilia. In the present study, we defined four modulatory peptide analogues of OVA323-339 with comparable MHC class II binding affinity. These peptide analogues were used for immunotherapy by s.c. injection in OVA-sensitized mice before OVA challenge. Compared with vehicle-treated mice, treatment with the Th2-skewing wild-type peptide and a Th2-skewing partial agonistic peptide (335N-A) dramatically increased airway eosinophilia upon OVA challenge. In contrast, treatment with a Th1-skewing peptide analogue (336E-A) resulted in a significant decrease in airway eosinophilia and OVA-specific IL-4 and IL-5 production. Our data show for the first time that a Th1-skewing peptide analogue of a dominant allergen epitope can modulate allergen-specific Th2 effector cells in an allergic response in vivo. Furthermore, these data suggest that the use of Th1-skewing peptides instead of wild-type peptide may improve peptide immunotherapy and may contribute to the development of a successful and safe immunotherapy for allergic patients.

Liposomes in autoimmune diseases: selected applications in immunotherapy and inflammation detection

In this contribution three examples are discussed of ongoing research where liposomes are used as carrier systems for immunotherapy and inflammation detection in autoimmune diseases. Liposomes can be used as carrier systems of antigenic peptides to peripheral blood mononuclear cells. The second example deals with their use as carrier systems for MHC-peptide complexes for multivalent Ag-presentation to autoreactive T lymphocytes to specifically modulate the activity of these T lymphocytes. The third example relates to our work on long circulating liposomes which are currently being tested in man for their potential to image inflammation sites.

Competition for antigenic sites during T cell proliferation: a mathematical interpretation of in vitro data

By fitting different mathematical T cell proliferation functions to in vitro T cell proliferation data, we studied T cell competition for stimulatory signals. In our lymphocyte proliferation assays both the antigen (Ag) availability and the concentration of T cells were varied. We show that proliferation functions involving T cell competition describe the data significantly better than classical proliferation functions without competition, thus providing direct evidence for T cell competition in vitro. Our mathematical approach allowed us to study the nature of T cell competition by comparing different proliferation functions involving (i) direct inhibitory T-T interactions, (ii) Ag-specific resource competition, or (iii) resource competition for nonspecific factors such as growth factors, and access to the surface of Ag-presenting cells (APCs). We show that resource competition is an essential ingredient of T cell proliferation. To discriminate between Ag-specific and nonspecific resource competition, the Ag availability was varied in two manners. In a first approach we varied the concentration of APCs, displaying equal ligand densities; in a second approach we varied the Ag density on the surface of the APCs, while keeping the APC concentration constant. We found that both resource competition functions described the data equally well when the Ag availability was increased by adding APCs. When the APC concentration was kept constant, the nonspecific resource competition function yielded the best description of the data. Our interpretation is that T cells were competing for "antigenic sites" on the APCs.

Opposite effects of immunotherapy with ovalbumin and the immunodominant T-cell epitope on airway eosinophilia and hyperresponsiveness in a murine model of allergic asthma

In the present study, we investigated immunotherapy using an entire protein or an immunodominant epitope in a murine model of allergic asthma. Immunotherapy was performed in ovalbumin (OVA)-sensitized mice before OVA challenge. Mice were treated subcutaneously with OVA, the immunodominant epitope OVA323-339, or vehicle. In vehicle-treated animals, repeated OVA challenge induced increased serum levels of OVA-specific immunoglobulin (Ig)G1, IgE, airway eosinophilia, and hyperresponsiveness, compared with saline-challenged animals. In addition, interleukin (IL)-4 and IL-5 production upon OVA restimulation of lung-draining lymph node cells in vitro were significantly increased in OVA-challenged animals. Immunotherapy using OVA significantly reduced airway eosinophilia and hyperresponsiveness. This finding was accompanied by significantly reduced OVA-specific IL-4 and IL-5 production. Further, OVA immunotherapy induced increased serum levels of OVA-specific IgG1, whereas OVA-specific IgG2a and IgE levels were not affected. In contrast to OVA immunotherapy, immunotherapy with OVA323-339 aggravated airway eosinophilia and hyperresponsiveness. OVA-specific IgG1, IgG2a, and IgE serum levels, and in vitro IL-4 and IL-5 production, were not affected. Thus, immunotherapy with protein resulted in beneficial effects on airway eosinophilia and hyperresponsiveness, which coincided with a local reduced T-helper 2 (Th2) response. In contrast, peptide immunotherapy aggravated airway hyperresponsiveness and eosinophilia, indicating a local enhanced Th2 response.

Antigen presentation by T cells versus professional antigen-presenting cells (APC): differential consequences for T cell activation and subsequent T cell-APC interactions

We compared the effects of antigen (Ag) presentation by T cells and professional antigen-presenting cells (APC) on T cell proliferation, cytokine production and surface molecule expression. Ag presentation by T cells (T-T presentation) induced an initial T cell activation phase as measured by proliferation and IL-2 production. These activated T cells became anergic upon antigenic restimulation by professional APC, as shown by a failure to proliferate or produce IL-2 or IFN-gamma. Interestingly, such T cells were not intrinsically defective in their signal transduction pathways since they did proliferate and produce cytokines upon restimulation with mitogenic stimuli. Flow cytometric analysis revealed a more profound TCR and CD3 down-regulation during T-T presentation than during APC-T presentation. However, no up-regulation of CD80, CD86, CD45RC and OX40 (CD134) was observed on T cells during T-T presentation or subsequent antigenic restimulation of anergic T cells in the presence of professional APC, whereas increased expression of these molecules was observed during professional APC-T presentation of non-anergic T cells. The impaired expression of co-stimulatory and activation molecules on T cells after T-T presentation of Ag might lead to altered interactions between T cells and professional APC upon antigenic restimulation. We propose that T cell anergy is a functional consequence of these altered T cell-APC interactions.

Dose-dependent induction of distinct anergic phenotypes: multiple levels of T cell anergy

T cell anergy has been proposed as one of the mechanisms underlying peripheral T cell tolerance. In recent years, the functional relevance of T cell anergy has been studied extensively in vitro and in vivo, using different species, cell systems, and ways to induce anergy. Although these studies concurred about the induction of unresponsiveness, conflicting findings were obtained with respect to the function of anergic T cells and to the persistence of T cell anergy. In the present study, T cell anergy was induced through T-T presentation of the specific Ag by rat MHC class II+ T cells in the absence of professional APC. We show that, depending on the Ag dose with which T cells were incubated, distinct anergic phenotypes were induced. Incubation of T cell clones with a low (suboptimal) Ag dose induced hyporesponsiveness. Incubation with a higher (optimal) Ag dose induced an anergic state capable of exerting immunoregulatory effects. Incubation with a high (supraoptimal) Ag dose led to an anergic suppressive phenotype that was persistent and was not reversed by APC, Ag, and rIL-2. These findings demonstrate that T cell anergy is not confined to a single state of functional inactivation. Instead, multiple levels of T cell anergy exist. Thus, anergic T cells can contribute to the regulation of the immune response either in a persistent and active manner or in a passive manner, depending on their level of T cell anergy.

Liposomes with incorporated MHC class II/peptide complexes as antigen presenting vesicles for specific T cell activation

PURPOSE

The purpose of this study was to design a well-characterized liposomal carrier system for multivalent antigen presentation in order to activate T cells.

METHODS

MHC class II molecules were loaded with peptide and subsequently reconstituted into liposomes. A FACS assay was developed to monitor peptide loading and MHC class II incorporation in the liposomes. For in vitro testing of the resulting MHC class II/peptide liposomes, a T cell hybridoma assay was employed.

RESULTS

The FACS assay provided a qualitative means to visualize the amount of incorporated MHC class II and peptide molecules that were oriented in the appropriate way for antigen presentation to the T cells. Interestingly, when MHC class II molecules were loaded with the appropriate peptide prior to liposome incorporation, such liposomes were fully capable of inducing IL-2 production of a T cell hybridoma.

CONCLUSIONS

This is the first article showing that MHC class II/peptide liposomes can serve as 'artificial antigen presenting cells' for activation of a CD4+ T cell hybridoma. As compared to soluble MHC class II/peptide complexes, the multivalency of liposomal complexes may be an important advantage when studying possible applications in immunotherapy.

Critical requirement for aspartic acid at position 82 of myelin basic protein 73-86 for recruitment of V beta 8.2+ T cells and encephalitogenicity in the Lewis rat

We synthesized single amino acid-substituted peptide analogues of guinea pig myelin basic protein (MBP) 73-86 to study the importance of aspartic acid at residue 82 (QKSQRSQDENPV), which previous reports have suggested is a critical TCR contact residue. Whereas the wild-type 73-86 peptide elicited severe experimental autoimmune encephalomyelitis (EAE) in the Lewis rat, none of the peptide analogues with substitutions at position 82 were capable of inducing EAE. The inability to cause EAE was not due to a failure to bind MHC or to elicit T cell proliferation and cytokine secretion. T cells specific for MBP73-86 did not cross-react with any of the analogues tested, further indicating the importance of this residue in T cell responses to 73-86. Analysis by flow cytometry showed that only the wild-type 73-86 peptide was capable of recruiting V beta 8.2+ T cells, which have been shown previously to be important for disease induction. Reduced expression of the V beta 8.2 TCR was also seen in Lewis rats protected from EAE by coimmunization of MBP73-86 with 73-86(82D-->A), despite an increase in cytokine production when both peptides were present during in vitro culture. The data indicate that aspartic acid 82 is a critical TCR contact residue and is required for the recruitment of V beta 8.2+ T cells and the encephalitogenic activity of MBP73-86.

Anergic T cells actively suppress T cell responses via the antigen-presenting cell

We here show that anergic T cells are active mediators of T cell suppression. In co-culture experiments, we found that anergic T cells, derived from established rat T cell clones and rendered anergic via T cell presentation of the specific antigen (Ag), were active inhibitors of T cell responses. Anergic T cells inhibited not only the responses of T cells with the same Ag specificity as the anergic T cells, but were also capable of efficiently inhibiting polyclonal T cell responses directed to other epitopes. This suppression required close cell-cell contact between antigen-presenting cells (APC), anergic T cells and responder T cells, and only occurred when the epitope recognized by the anergic T cell was present. The suppression was not caused by passive competition for ligands on the APC surface, IL-2 consumption, or cytolysis, and was not mediated by soluble factors derived from anergic T cells that were stimulated with their specific Ag. When responder T cells were added 24 h after co-culturing anergic cells in the presence of Ag and APC, T cell responses were still suppressed, indicating that the suppressive effect was persistently present. However, anergic T cells were not able to suppress responder T cells that had already received a full activation signal. We propose that suppression by anergic T cells is mediated via the APC, either through modulation of the T cell-activating capacity of the APC (APC/T cell interaction), or by inhibition of T cells recognizing their ligand in close proximity on the same APC (T/T cell interaction).

Heat-shock protein T-cell epitopes trigger a spreading regulatory control in a diversified arthritogenic T-cell response

Adjuvant arthritis (AA) in Lewis rats is T-cell mediated and seems to depend on T cells recognising the 180-188 epitope of mycobacterial heat-shock protein (hsp) 60. Analysis of arthritogenic T-cell clone A2b has revealed a mimicry of this particular epitope with an articular cartilage-associated target T-cell epitope. Nasal administration of synthetic peptides covering this 180-188 sequence led to epitope-specific tolerance and resistance to AA. Since this tolerisation protocol also inhibited avridine arthritis, one may conclude that this form of epitope-specific tolerance had effectuated a spreading tolerisation at the level of target antigens that included a diverse set of possible arthritis-associated antigens. In vitro anergised T cells exhibited suppressive activity in a co-culture system. As in this case--depending on the presence of the antigen of the anergic T cell--such T cells suppressed responder T cells of a different antigenic specificity, we postulated that anergic T cells may be responsible for a spreading of tolerance. It seemed that such spreading of tolerance was channelled through the antigen-presenting cells (APC) and was dependent on direct cell-cell contact. This and additional forms of spreading of tolerance could be responsible for specific nasal tolerance, causing inhibition of the development of an arthritogenic inflammatory response. This can be similarly the case for the arthritis protection that resulted from immunisation with hsps. Analysis of T-cell responses following hsp immunisations revealed that the arthritis inhibitory activity resided in T cells with specificity for a conserved part of microbial hsp 60. The same T cells cross-responded to rat self-hsp60. Low level expression of the latter molecule on non-professional APC could possibly have induced a suppressive anergic state in these autoreactive cells. Thus, immunisation with microbial hsp would have led to an expansion of such T cells, leading to raised disease-suppressive potential when selectively trapped and activated in the inflamed self-hsp-overexpressing joint. Alternatively, the cross-recognised self-hsp epitope could have the regulatory qualities of an altered peptide ligand or a partial agonist for T cells that see the microbial homologue as the full agonist.

Definition of an extended MHC class II-peptide binding motif for the autoimmune disease-associated Lewis rat RT1.BL molecule

The Lewis rat, an inbred rat strain susceptible to several well-characterized experimental autoimmune diseases, provides a good model to study peptide-mediated immunotherapy. Peptide immunotherapy focussing on the modulation of T cell responses by interfering with TCR-peptide-MHC complex formation requires the elucidation of the molecular basis of TCR-peptide-MHC interactions for an efficient design of modulatory peptides. In the Lewis rat most autoimmune-associated CD4+ T cell responses are MHC class II RT1.BL restricted. In this study, the characteristics of RT1.BL-peptide interactions were explored. A series of substitution analogs of two Lewis rat T cell epitopes was examined in a direct peptide-MHC binding assay on isolated RT1.BL molecules. Furthermore, other autoimmune-related as well as non-disease-related T cell epitopes were tested in the binding assay. This has led to the definition of an extended RT1.BL-peptide binding motif. The RT1.BL-peptide binding motif established in this study is the first described rat MHC-peptide binding motif based on direct MHC-peptide binding experiments. To predict good or intermediate RT1.BL binding peptides, T cell epitope search profiles were deduced from this motif. The motif and search profiles will greatly facilitate the prediction of modulatory peptides based on autoimmune-associated T cell epitopes and the identification of target structures in experimental autoimmune diseases in Lewis rats.

Inhibition of experimental autoimmune myasthenia gravis by major histocompatibility complex class II competitor peptides results not only in a suppressed but also in an altered immune response

To assess the capacity of major histocompatibility complex (MHC) class II-binding competitor peptides in inhibiting antibody-mediated disease processes, we studied experimental autoimmune myasthenia gravis in Lewis rats. Experimental autoimmune myasthenia gravis, a disease model mediated by T cell-dependent autoantibodies against acetylcholine receptors, was induced by immunization with Torpedo californica acetylcholine receptor emulsified in complete Freund's adjuvant. The immunodominant acetylcholine receptor T cell epitope was recognized by T cells in the context of MHC class II RT1.B(L). The disease inhibitory capacity of RT1.B(L)-binding peptides not related to the acetylcholine receptor was determined upon co-immunization with Torpedo acetylcholine receptor. Co-immunization of peptide OVA323-339, a strong RT1.B(L)-binding competitor peptide, resulted in complete disease inhibition. Although, the priming of the anti-acetylcholine receptor T cell response was not fully inhibited, the kinetics of the response was changed. Moreover, besides a drastic reduction of the anti-Torpedo acetylcholine receptor antibody titers, a shift in isotype distribution was found. These findings indicate that antibody-mediated autoimmune processes can be suppressed by MHC class II competitor peptides. Furthermore, the administration of such peptides in vivo not only passively inhibits T cell activation, but also functionally alters the immune response.

Quaternary structure of a carrier protein influences antigenicity and immunogenicity of an inserted T cell determinant

To study the influence of the quaternary structure of the outer membrane protein PhoE of Escherichia coli on the presentation of an inserted T cell epitope, an epitope comprising amino acid residues 72-85 of myelin basic protein (MBP) was inserted at different sites in PhoE. This sequence is the critical T cell epitope in experimental autoimmune encephalomyelitis (EAE) in Lewis rats. The antigenicity and immunogenicity of two different conformational forms of the chimeric PhoE constructs, i.e. the denatured monomeric form and the native trimeric form, were studied. It appeared that the monomeric form, but not the native trimeric form of such PhoE constructs induced proliferation of the MBP72-85-specific T cell line Z1a. This conformational discrepancy was independent of the site in PhoE in which the epitope was inserted. Immunization with the monomeric form of PhoE constructs resulted in the priming of MBP72-85-specific T cells. In contrast, the trimeric form of these constructs was much less efficient in priming such cells. The differences between the monomeric and trimeric forms were most apparent when induction of EAE was studied. The monomeric form was encephalitogenic while the trimeric form was not. Furthermore, the antigen fine specificity, Vbeta usage and encephalitogenicity of T cells triggered by immunization with a monomeric PhoE construct appeared to be the same as those of T cell line Z1a, which was obtained after immunization with MBP, indicating that similar cells are triggered by immunization with the epitope either in PhoE or in its native context.

(Altered) self peptides and the regulation of self reactivity in the peripheral T cell pool

Tolerance for self has appeared incomplete for many self antigens. We have obtained experimental evidence that both for self heat shock proteins and T cell receptor V-gene products, reactive T cells are part of the normal immune repertoire. Furthermore, it has become apparent that stimulation of T cell responsiveness to these antigens, by using peptide immunisation or by transfer of activated T cells, raises resistance to experimentally induced autoimmune arthritis. In addition, available evidence has suggested that these reactivities may be functional during natural processes of disease remission. The observations with regard to heat-shock proteins have indicated that mechanism leading to disease resistance are most efficiently triggered by exposing the immune system to non-self antigens such as bacterial hsp's, which are similar to, but not identical to, self. Experimental evidence has been obtained, that conserved bacterial hsp peptides, may trigger self hsp reactive T cells, with disease suppressive regulatory potential. It is possible that such self hsp reactive T cells, being expanded by recognising bacterial peptides as full agonists, do, in fact, perceive the self epitopes as partial agonists, and therefore have the possibility of displaying downregulatory activity at the site of inflammation. Experiments with peptide analogs of self epitopes, being variants of disease critical T cell epitopes, have indeed suggested that also their activity in modulating disease may comply with the principles of dominant immunological tolerance.

Activated rat T cells synthesize and express functional major histocompatibility class II antigens

In the present report, we studied the presence and functional significance of major histocompatibility complex (MHC) class II antigen on rat T cells. Most rat T-cell lines cultured in vitro were found to be MHC class II+. Also, these T-cell lines were shown to synthesize MHC class II molecules. Immunohistochemical and flow cytometric double stainings for T-cell receptor (TCR) and MHC class II showed that in vivo as well a large proportion of T cells was MHC class II+. The immunohistochemical staining of spleen sections enabled us to characterize the MHC class II+ and MHC class II- T cells. It was shown that resting T cells in vivo were MHC class II-. In contrast, activated T cells, as determined by their localization in the marginal zone of the spleen, proved to be MHC class II+. Finally, T-cell clones were found to be able to present peptidic antigens, but could only poorly present more complex exogenous antigens, probably due to inefficient uptake of such antigens. These features would endow activated rat T cells with the capacity to present cell-specific self-proteins, such as TCR, to regulatory CD4+ MHC class II-restricted T cells, as was described by our group elsewhere.

Direct binding of autoimmune disease related T cell epitopes to purified Lewis rat MHC class II molecules

New strategies applied in the treatment of experimental autoimmune disease models involve blocking or modulation of MHC-peptide-TCR interactions either at the level of peptide-MHC interaction or, alternatively, at the level of T cell recognition. In order to identify useful competitor peptides one must be able to assess peptide-MHC interactions. Several well described autoimmune disease models exist in the Lewis rat and thus this particular rat strain provides a good model system to study the effect of competitor peptides. So far no information has been available on the peptide binding characteristics of the Lewis rat MHC class II RT1.B1 molecule. We have now developed a biochemical binding assay which enables competition studies in which the relative MHC binding affinity of a set of non-labelled peptides can be assessed while employing detection of biotinylated marker peptides by chemiluminescence. The assay is sensitive and specific. We have used this assay to determine the binding characteristics of several disease associated T cell determinants and their sequence analogues in the Lewis rat. Notably, most of the autoimmune disease associated peptide sequences tested were found to be intermediate to poor binders. Single amino acid substitutions at defined positions were sufficient to turn certain peptides into good binders. These results are relevant to the design of competitor peptides in the treatment of experimental autoimmune diseases.

Inhibition of entire myelin basic protein-induced experimental autoimmune encephalomyelitis in Lewis rats by major histocompatibility complex class II-binding competitor peptides

Previous studies have shown that major histocompatibility complex (MHC) blockade by competitor peptides with high MHC class II binding affinity can prevent peptide-induced experimental autoimmune encephalomyelitis (EAE). However, none of these studies addressed the question whether this approach could also be used to prevent EAE induced with a multivalent antigen. In this report we show the effect of competitor peptides co-immunized during EAE induction with entire guinea pig myelin basic protein (MBP) in Lewis rats. As MHC class II binding competitor peptides we used one nonimmunogenic disease-nonrelated peptide, and two immunogenic peptides, one EAE-related and one non-EAE-related. The respective efficacy of these three competitor peptides to inhibit MBP-induced proliferation of an encephalitogenic T cell line in vitro correlated with their respective MHC binding affinity. Co-immunization of the competitor peptides during disease induction with entire MBP resulted in a competitor concentration-dependent inhibition of clinical signs of EAE. These results demonstrate that, although polyclonal T cell responses to MBP were not completely inhibited, co-administration of immunogenic or nonimmunogenic either EAE-related or non-EAE-related MHC class II binding competitor peptides can inhibit the development of EAE induced with entire MBP.

Inhibition of experimental autoimmune encephalomyelitis by MHC class II binding competitor peptides depends on the relative MHC binding affinity of the disease-inducing peptide

Blocking of the Ag presentation function of MHC molecules by competitor peptides has been proposed as a potential immunotherapy for MHC-associated autoimmune diseases. Despite the fact that successful inhibition of experimental autoimmune encephalomyelitis (EAE) by coimmunization with competitor peptides had been achieved, it remained questionable whether the in vivo activity of such peptides was solely the result of MHC blockade. In the peptide MBP72-85-induced EAE model in Lewis rats, we designed a single amino acid-substituted analogue of MBP72-85 with a superior MHC binding capacity, and with the capacity to activate encephalitogenic MBP72-85-specific T cells. Subsequently, two well-defined competitor peptides, one EAE related and one non-EAE related, were studied for their respective efficacies to inhibit the in vitro proliferation of an encephalitogenic T cell clone induced by the original MBP72-85 or the superior MHC binding analogue peptide. It appeared that the response to MBP72-85 was inhibited very efficiently by both competitor peptides, whereas the response to the superior MHC binding analogue peptide was not. Co-immunization of either the related or non-related competitor peptide together with MBP72-85 inhibited EAE induction in a concentration-dependent manner. In such protected rats, polyclonal T cell responses against MBP72-85 were dramatically decreased. However, EAE induced by the stronger MHC binding MBP72-85 analogue could not be inhibited by either of the competitor peptides. Moreover, in these rats, T cell priming for both MBP72-85 and the MBP72-85 analogue was not inhibited. These results show that competition for MHC binding in vivo could lead to inhibition of EAE induction.

Inhibition of experimental autoimmune encephalomyelitis by MHC class II binding competitor peptides depends on the relative MHC binding affinity of the disease-inducing peptide

Blocking of the Ag presentation function of MHC molecules by competitor peptides has been proposed as a potential immunotherapy for MHC-associated autoimmune diseases. Despite the fact that successful inhibition of experimental autoimmune encephalomyelitis (EAE) by coimmunization with competitor peptides had been achieved, it remained questionable whether the in vivo activity of such peptides was solely the result of MHC blockade. In the peptide MBP72-85-induced EAE model in Lewis rats, we designed a single amino acid-substituted analogue of MBP72-85 with a superior MHC binding capacity, and with the capacity to activate encephalitogenic MBP72-85-specific T cells. Subsequently, two well-defined competitor peptides, one EAE related and one non-EAE related, were studied for their respective efficacies to inhibit the in vitro proliferation of an encephalitogenic T cell clone induced by the original MBP72-85 or the superior MHC binding analogue peptide. It appeared that the response to MBP72-85 was inhibited very efficiently by both competitor peptides, whereas the response to the superior MHC binding analogue peptide was not. Co-immunization of either the related or non-related competitor peptide together with MBP72-85 inhibited EAE induction in a concentration-dependent manner. In such protected rats, polyclonal T cell responses against MBP72-85 were dramatically decreased. However, EAE induced by the stronger MHC binding MBP72-85 analogue could not be inhibited by either of the competitor peptides. Moreover, in these rats, T cell priming for both MBP72-85 and the MBP72-85 analogue was not inhibited. These results show that competition for MHC binding in vivo could lead to inhibition of EAE induction.

Differential rat T cell recognition of cathepsin D-released fragments of mycobacterial 65 kDa heat-shock protein after immunization with either the recombinant protein or whole mycobacteria

T cells specific for the mycobacterial 65 kDa heat-shock protein (hsp65) play a pivotal role in the development of adjuvant arthritis (AA) in Lewis rats. Upon adoptive transfer, CD4+ T cells recognizing a particular hsp65 epitope trigger the onset of disease. Activation of hsp65-reactive T cells can be achieved by immunization with heat-killed mycobacteria in mineral oil--complete Freund's adjuvant (CFA)--or with purified recombinant hsp65. Arthritis, however, will only develop after immunization with CFA. In fact, preimmunization with hsp65 protects against any subsequent attempt to induce AA. In this study, we examined polyclonal lymph node cell responses in Lewis rats, immunized with either CFA or purified recombinant hsp65 in incomplete Freund's adjuvant, to a set of hsp65 fragments generated by a mild digestion with cathepsin D. Proliferative responses to several hsp65 fragments varied with the type of antigen used for immunization. A cathepsin D-released fragment, identified as residues 376-408, preferentially triggered proliferation of rat T cells after hsp65 immunization. Preimmunization of Lewis rats with this peptide delayed the onset and reduced the severity of AA. Preimmunization with another fragment which was preferentially recognized after CFA immunization, representing residues 40-60, did not have such a protective effect. Our findings suggest the presence of mycobacterial hsp65 determinants that selectively trigger AA-regulating T cells and illustrate that cathepsin D may be used as an experimental tool to generate such determinants.

A peptide variant of an arthritis-related T cell epitope induces T cells that recognize this epitope as a synthetic peptide but not in its naturally processed form

The immune system has the potential to utilize a diverse T cell repertoire for the recognition of Ag in the context of MHC molecules. Here we describe the analysis of two rat T cell clones, both of which recognize a synthetic peptide comprised of the arthritis-associated 180-188 amino acid sequence of the mycobacterial 65-kDa heatshock protein (hsp65 180-188), but which differ in the recognition of the naturally processed hsp65. The arthritogenic T cell clone A2b, generated by immunization with whole Mycobacterium tuberculosis, recognized the hsp65 180-188 synthetic peptide as well as the processed hsp65, whereas T cell clone ATL11, generated after immunization with a single amino acid substituted peptide analog of hsp65 180-188, recognized peptide hsp65 180-188 but not the processed hsp65. For both T cell clones the minimal stimulatory sequence was hsp65 180-186. However, within this minimal stimulatory sequence marked differences between the clones were found with regard to peptide residues interacting with the TCR. Furthermore, addition of extra residues at the N terminus of the hsp65 180-186 sequence abrogated the recognition by clone ATL11, but not by A2b. These findings demonstrate that, upon in vivo immunization with a synthetic peptide comprised of a single amino acid variant of a T cell epitope, T cells can be triggered that recognize a peptide comprised of the original epitope sequence, but that do not recognize this epitope in its naturally processed protein fragment. The possibility of triggering such T cells by immunization with synthetic peptides, may well have consequences for the design of peptide vaccines or peptide immunomodulatory agents.

A peptide variant of an arthritis-related T cell epitope induces T cells that recognize this epitope as a synthetic peptide but not in its naturally processed form

The immune system has the potential to utilize a diverse T cell repertoire for the recognition of Ag in the context of MHC molecules. Here we describe the analysis of two rat T cell clones, both of which recognize a synthetic peptide comprised of the arthritis-associated 180-188 amino acid sequence of the mycobacterial 65-kDa heatshock protein (hsp65 180-188), but which differ in the recognition of the naturally processed hsp65. The arthritogenic T cell clone A2b, generated by immunization with whole Mycobacterium tuberculosis, recognized the hsp65 180-188 synthetic peptide as well as the processed hsp65, whereas T cell clone ATL11, generated after immunization with a single amino acid substituted peptide analog of hsp65 180-188, recognized peptide hsp65 180-188 but not the processed hsp65. For both T cell clones the minimal stimulatory sequence was hsp65 180-186. However, within this minimal stimulatory sequence marked differences between the clones were found with regard to peptide residues interacting with the TCR. Furthermore, addition of extra residues at the N terminus of the hsp65 180-186 sequence abrogated the recognition by clone ATL11, but not by A2b. These findings demonstrate that, upon in vivo immunization with a synthetic peptide comprised of a single amino acid variant of a T cell epitope, T cells can be triggered that recognize a peptide comprised of the original epitope sequence, but that do not recognize this epitope in its naturally processed protein fragment. The possibility of triggering such T cells by immunization with synthetic peptides, may well have consequences for the design of peptide vaccines or peptide immunomodulatory agents.

Disease inhibition by major histocompatibility complex binding peptide analogues of disease-associated epitopes: more than blocking alone

Peptide analogues of disease-associated epitopes were studied for inhibition of experimental allergic encephalomyelitis (EAE) and adjuvant arthritis (AA) in Lewis rats. EAE- and AA-associated analogues were selected as competitors because of their in vitro inhibitory activity on proliferation of encephalitogenic and arthritogenic T cells. Although the EAE-associated competitor had a superior major histocompatibility complex (MHC) binding affinity, the AA-associated competitor was a better inhibitor of the in vitro proliferation of arthritogenic T cells. Furthermore, although in vivo EAE was inhibited by both competitors, AA was only inhibited by the AA-associated competitor. Remarkably, in contrast to what was expected of a regular MHC competitor peptide, the AA-associated peptide analogue also prevented AA upon immunization before disease induction and appeared to induce T cell responses that crossreacted with the original disease-associated epitope. Therefore, it is concluded that antigen-specific regulatory mechanisms were involved in synergy with MHC competition. The integration of both qualities into a single "competitor-modulator" analogue peptide may lead to the development of novel, more effective, disease-specific immunomodulatory peptides.

Towards peptide immunotherapy in rheumatoid arthritis: competitor-modulator concept

By the introduction of single-amino acid substitutions in well-defined T cell epitopes of autoimmunogenic proteins, e.g., mycobacterial heat shock protein (hsp60) in adjuvant arthritis (AA) and myelin basic protein (MBP) in experimental allergic encephalomyelitis (EAE), efficiently blocking MHC binding peptides were selected. Despite the finding that a substituted variant of epitope 180-188 of hsp60 was 'blocking' not only responses of the 180-188 specific arthritogenic T cell A2b, but also responses of the MBP specific encephalitogenic T cell Z1a, in vivo testing of this competitor peptide revealed a very prominent disease inhibitory activity in AA but not in MBP-induced EAE. The selectivity of this peptide in suppressing the disease in which native 180-188 appears to be of critical relevance, offers the possibility of achieving disease specific immunological intervention. Based on the results collected so far, it seems that, in vivo in addition to blocking activity, a variant peptide itself could trigger responses that confer protective activity in AA. Such combined activities may well be required for achieving full in vivo inhibition of a disease in which multiple distinct epitopes may play a role, possibly through presentation by more than one MHC product.

T cell reactivity to an epitope of the mycobacterial 65-kDa heat-shock protein (hsp 65) corresponds with arthritis susceptibility in rats and is regulated by hsp 65-specific cellular responses

Adjuvant arthritis (AA) can be induced in genetically susceptible rats by immunization with heat-killed mycobacteria suspended in mineral oil. From our analysis of arthritogenic T cell clone A2b, obtained from an arthritic Lewis rat and specific for the 180-188 epitope of mycobacterial 65-kDa heat-shock protein (hsp 65), the possible origin of AA was explained by the existence of a molecular mimicry of the 180-188 epitope with a cartilage-associated self antigen. We now have shown that Lewis rats respond to the 180-188 epitope after Mycobacterium tuberculosis immunization and that arthritis-resistant Fisher and (Lewis x Fisher)F1 rats, although major histocompatibility complex class II identical with Lewis, do not respond to this epitope. However, in rare cases of arthritis in Fisher rats, responses to the epitope were seen. We obtained no evidence for a defect at the level of antigen processing and presentation or for suppression in Fisher rats. Thus, non-responsiveness in Fisher rats was likely due to a difference at the level of the T cell repertoire. Previously, we have reported that pretreatment with hsp 65 in experimental arthritis, and not only in AA, caused resistance to arthritis induction. We now present evidence that immunization with hsp 65 or in vitro stimulation with hsp 65 may lead to inhibition of responses specific for epitope 180-188. Thus the hsp 65-induced resistance to arthritis is probably caused by the induction of regulatory control specifically targeted at the 180-188 epitope. Especially in rats that tend to focus their responses on the critical 180-188 sequence, such as Lewis, regulation seems to develop following immunization with hsp 65. Since recent evidence suggests that hsp 65 and also the 180-188 epitope have a role in human arthritic conditions, the present findings are expected to contribute to further experimentation directed at exploiting hsp 65 or its epitopes for the development of new therapeutical approaches in humans.

CD4 rat x rat and mouse x rat T cell hybridomas produced by fusion of established T cell lines and clones to W/Fu (C58NT)D

Previously, fusion of established T cell lines or clones has been claimed to be difficult. We now report our experiences in the fusion of both long term cultures of rat T cell clones and mouse T cell lines to rat W/Fu (C58NT)D. Upon fusion of rat T cell clones the hybrids obtained expressed antigen specificities identical to those of the parent clones. In addition, C58 was used for interspecies hybridisation of murine T cell lines. The specificity of intra- and inter-species hybrids was maintained by subcloning. We conclude that the C58 cell line can be used to generate continuously growing monoclonal T-cell reagents of sufficient stability using both intra- and inter-species hybridisation.