Alteration of a model antigen by Au(III) leads to T cell sensitization to cryptic peptides

Palladium-Induced Temporal Internalization of MHC Class I Contributes to T Cell-Mediated Antigenicity

Palladium (Pd) is a widely used metal and extremely important biomaterial for the reconstruction of occlusions during dental restorations. However, metallic biomaterials can cause serious allergic reactions, such as Pd-related oral mucositis seen in dentistry. Metal allergy is categorized as a type IV allergy and we demonstrated that CD8 T cells play an important role in Pd allergy previously. As TCR of CD8 T cells recognizes MHC class I/peptide complex, the antigen specificity to this complex seems to be generated during Pd allergy. However, it remains unknown if Pd affects the MHC class I/peptide complex. In this study, we investigated the behavior of the MHC class I/peptide complex in response to Pd treatment. We found that PdCl₂ treatment altered peptide presentation on MHC class I and that co-culture with Pd-treated DC2.4 cells induced activation of Pd-responsive TCR-expressing T cell line. Furthermore, PdCl₂ treatment induced temporal MHC class I internalization and inhibition of membrane movement suppressed Pd-induced T cell-mediated antigenicity. These data suggest that Pd-induced MHC class I internalization is critical for generation of antigenicity through a mechanism including differential peptide loading on MHC class I, which results in Pd allergy.

Immunological Mechanisms of Metal Allergies and the Nickel-Specific TCR-pMHC Interface

Besides having physiological functions and general toxic effects, many metal ions can cause allergic reactions in humans. We here review the immune events involved in the mediation of metal allergies. We focus on nickel (Ni), cobalt (Co) and palladium (Pd), because these allergens are among the most prevalent sensitizers (Ni, Co) and immediate neighbors in the periodic table of the chemical elements. Co-sensitization between Ni and the other two metals is frequent while the knowledge on a possible immunological cross-reactivity using in vivo and in vitro approaches remains limited. At the center of an allergic reaction lies the capability of a metal allergen to form T cell epitopes that are recognized by specific T cell receptors (TCR). Technological advances such as activation-induced marker assays and TCR high-throughput sequencing recently provided new insights into the interaction of Ni2+ with the αβ TCR-peptide-major histocompatibility complex (pMHC) interface. Ni2+ functionally binds to the TCR gene segment TRAV9-2 or a histidine in the complementarity determining region 3 (CDR3), the main antigen binding region. Thus, we overview known, newly identified and hypothesized mechanisms of metal-specific T cell activation and discuss current knowledge on cross-reactivity.

Gas Plasma Technology Augments Ovalbumin Immunogenicity and OT-II T Cell Activation Conferring Tumor Protection in Mice

Reactive oxygen species (ROS/RNS) are produced during inflammation and elicit protein modifications, but the immunological consequences are largely unknown. Gas plasma technology capable of generating an unmatched variety of ROS/RNS is deployed to mimic inflammation and study the significance of ROS/RNS modifications using the model protein chicken ovalbumin (Ova vs oxOva). Dynamic light scattering and circular dichroism spectroscopy reveal structural modifications in oxOva compared to Ova. T cells from Ova-specific OT-II but not from C57BL/6 or SKH-1 wild type mice presents enhanced activation after Ova addition. OxOva exacerbates this activation when administered ex vivo or in vivo, along with an increased interferon-gamma production, a known anti-melanoma agent. OxOva vaccination of wild type mice followed by inoculation of syngeneic B16F10 Ova-expressing melanoma cells shows enhanced T cell number and activation, decreased tumor burden, and elevated numbers of antigen-presenting cells when compared to their Ova-vaccinated counterparts. Analysis of oxOva using mass spectrometry identifies three hot spots regions rich in oxidative modifications that are associated with the increased T cell activation. Using Ova as a model protein, the findings suggest an immunomodulating role of multi-ROS/RNS modifications that may spur novel research lines in inflammation research and for vaccination strategies in oncology.

Of self-lipids, CD1-restricted T cells, and contact sensitization

Contact hypersensitivity (CHS) in rodents and contact dermatitis in humans are long-known pathological conditions caused by MHC-restricted T-cell responses. These responses are triggered upon T-cell recognition of neo-antigenic determinants, which are generated by a variety of environmental contact sensitizer (CS) chemicals associating with self-proteins to comprise these neo-antigens. In this issue of the European Journal of Immunology, Betts et al. [Eur. J. Immunol. 2017. 47: 1171-1180] provide intriguing data implying that common small molecule CSs such as dinitrochlorobenzene can also recruit and activate autoreactive CD1-restricted T cells specific for cell-endogenous lipids, which are enriched in human skin. The effects of dinitrochlorobenzene on CD1 T-cell recruitment and function were dependent on newly synthesized CD1 molecules and the presence of endogenous lipids. These findings shed new light on unanticipated mechanisms that have potential clinical relevance on a common and highly distressing disease state.

Structural basis of metal hypersensitivity

Metal hypersensitivity is a common immune disorder. Human immune systems mount the allergic attacks on metal ions through skin contacts, lung inhalation and metal-containing artificial body implants. The consequences can be simple annoyances to life-threatening systemic illness. Allergic hyper-reactivities to nickel (Ni) and beryllium (Be) are the best-studied human metal hypersensitivities. Ni-contact dermatitis affects 10 % of the human population, whereas Be compounds are the culprits of chronic Be disease (CBD). αβ T cells (T cells) play a crucial role in these hypersensitivity reactions. Metal ions work as haptens and bind to the surface of major histocompatibility complex (MHC) and peptide complex. This modifies the binding surface of MHC and triggers the immune response of T cells. Metal-specific αβ T cell receptors (TCRs) are usually MHC restricted, especially MHC class II (MHCII) restricted. Numerous models have been proposed, yet the mechanisms and molecular basis of metal hypersensitivity remain elusive. Recently, we determined the crystal structures of the Ni and Be presenting human MHCII molecules, HLA-DR52c (DRA*0101, DRB3*0301) and HLA-DP2 (DPA1*0103, DPB1*0201). These structures revealed unusual features of MHCII molecules and shed light on how metal ions are recognized by T cells.

Drug-induced thrombocytopenia

Drug-induced thrombocytopenia (DIT) is a relatively common clinical disorder. It is imperative to provide rapid identification and removal of the offending agent before clinically significant bleeding or, in the case of heparin, thrombosis occurs. DIT can be distinguished from idiopathic thrombocytopenic purpura, a bleeding disorder caused by thrombocytopenia not associated with a systemic disease, based on the history of drug ingestion or injection and laboratory findings. DIT disorders can be a consequence of decreased platelet production (bone marrow suppression) or accelerated platelet destruction (especially immune-mediated destruction).

Exploring central and peripheral diversity in antibody evolution

The antigen-binding site, the paratope, of an antibody can be seen as being composed of a central core and a more peripheral area situated at its rim. Naturally these regions acquire their diversity using different mechanisms and they also have dissimilar roles, as they contribute differently to the binding interaction. Also, antigens of different size utilize these regions differently; while haptens mainly interact with the central core, larger antigens have additional interactions in more peripheral regions. Since haptens do not occupy the entire available paratope we hypothesized that hapten-specific antibodies, as they develop naturally or in the laboratory, have an imprint of the carrier protein they were once selected on. By using combinatorial library and phage display technologies on a hapten-specific antibody we were able to demonstrate that a peripheral carrier imprint indeed exists. We further show that such an imprint can act as a seed in the evolution of binders that recognize the carrier protein even in the absence of the hapten modification. The observed results provide a plausible mechanism for how haptenization of self-antigens can lead to the development of autoimmunity.

Recombinant HLA-DP2 binds beryllium and tolerizes beryllium-specific pathogenic CD4+ T cells

Chronic beryllium disease is a lung disorder caused by beryllium exposure in the workplace and is characterized by granulomatous inflammation and the accumulation of beryllium-specific, HLA-DP2-restricted CD4+ T lymphocytes in the lung that proliferate and secrete Th1-type cytokines. To characterize the interaction among HLA-DP2, beryllium, and CD4+ T cells, we constructed rHLA-DP2 and rHLA-DP4 molecules consisting of the alpha-1 and beta-1 domains of the HLA-DP molecules genetically linked into single polypeptide chains. Peptide binding to rHLA-DP2 and rHLA-DP4 was consistent with previously published peptide-binding motifs for these MHC class II molecules, with peptide binding dominated by aromatic residues in the P1 pocket. 9Be nuclear magnetic resonance spectroscopy showed that beryllium binds to the HLA-DP2-derived molecule, with no binding to the HLA-DP4 molecule that differs from DP2 by four amino acid residues. Using beryllium-specific CD4+ T cell lines derived from the lungs of chronic beryllium disease patients, beryllium presentation to those cells was independent of Ag processing because fixed APCs were capable of presenting BeSO4 and inducing T cell proliferation. Exposure of beryllium-specific CD4+ T cells to BeSO4 -pulsed, plate-bound rHLA-DP2 molecules induced IFN-gamma secretion. In addition, pretreatment of beryllium-specific CD4+ T cells with BeSO4-pulsed, plate-bound HLA-DP2 blocked proliferation and IL-2 secretion upon re-exposure to beryllium presented by APCs. Thus, the rHLA-DP2 molecules described herein provide a template for engineering variants that retain the ability to tolerize pathogenic CD4+ T cells, but do so in the absence of the beryllium Ag.

Noble metals strip peptides from class II MHC proteins

Class II major histocompatibility complex (MHC) proteins are essential for normal immune system function but also drive many autoimmune responses. They bind peptide antigens in endosomes and present them on the cell surface for recognition by CD4(+) T cells. A small molecule could potentially block an autoimmune response by disrupting MHC-peptide interactions, but this has proven difficult because peptides bind tightly and dissociate slowly from MHC proteins. Using a high-throughput screening assay we discovered a class of noble metal complexes that strip peptides from human class II MHC proteins by an allosteric mechanism. Biochemical experiments indicate the metal-bound MHC protein adopts a 'peptide-empty' conformation that resembles the transition state of peptide loading. Furthermore, these metal inhibitors block the ability of antigen-presenting cells to activate T cells. This previously unknown allosteric mechanism may help resolve how gold(I) drugs affect the progress of rheumatoid arthritis and may provide a basis for developing a new class of anti-autoimmune drugs.

Cross-presentation of a human malaria CTL epitope is conformation dependent

Little is known about the role of conformation on the antigen processing by antigen presenting cells. Using a well-defined antigen containing two disulfide bridges, the synthetic C-terminal fragment 282-383 derived from Plasmodium falciparum circumsporozoite protein (PfCS 282-383), we show that the reduced form is presented in vitro more efficiently than its oxidized counterpart, inducing stronger CTL recognition. In addition, only the reduced form can be presented by the TAP independent T2 cell line. Thus, the reduced form is processed by TAP dependent and independent pathways.

[Tolerance induction towards nickel. From animal model to humans]

Nickel is the most common contact allergen in humans. Until recently, many questions concerning tolerance mechanisms to nickel were unresolved. Besides human ex vivo, intervention and observation studies, the establishment of a reproducible mouse model has contributed to the analysis of these mechanisms. A more detailed understanding of the pathogenesis of nickel allergy and tolerance towards nickel by investigations in an animal model and in human studies is a prerequisite for developing specific prevention and therapy of nickel allergy. With this article, we provide a review of the investigations concerning nickel allergy and give perspectives towards oral tolerance induction to nickel in the animal model and in humans.

Autoimmunity and environmental factors in the pathogenesis of primary biliary cirrhosis

It is generally believed that autoimmune processes are initiated when tolerance to self-proteins is broken. Primary biliary cirrhosis (PBC) is an autoimmune liver disease of unknown etiology. Autoimmune attack in PBC is predominantly organ-specific, despite the presence of mitochondrial autoantigens, the major targets of autoimmunity in PBC, in all nucleated cells. Although the events that provoke initial activation remain unknown, the hypothesis of molecular mimicry implies that foreign pathogens with homology to self-protein or modified self-protein can break tolerance. Several reports have suggested the association of autoimmune diseases with drugs, chemicals, and other environmental factors. Specifically, many xenobiotics are metabolized in the liver. Liver autoantigens exposed to these chemicals could be modified and become immunogenic. We propose that exposure to the environmental xenobiotics is one of the initiating factors that leads to the loss of tolerance to self-proteins in genetically susceptible hosts, resulting in development of PBC.

Infectious nickel tolerance: a reciprocal interplay of tolerogenic APCs and T suppressor cells that is driven by immunization

Previously, we reported that tolerance to nickel, induced by oral administration of Ni(2+) ions, can be adoptively transferred to naive mice with only 10(2) splenic T cells. Here we show that 10(2) T cell-depleted spleen cells (i.e., APCs) from orally tolerized donors can also transfer nickel tolerance. This cannot be explained by simple passive transfer of the tolerogen. The APCs from orally tolerized donors displayed a reduced allostimulatory capacity, a tolerogenic phenotype, and an increased expression of CD38 on B cells. In fact, it was B cells among the APCs that carried the thrust of tolerogenicity. Through serial adoptive transfers with Ly5.1(+) donors and two successive sets of Ly5.2(+) recipients, we demonstrated that nickel tolerance was infectiously spread from donor to host cells. After the transfer of either T cells or APCs from orally tolerized donors, the spread of tolerance to the opposite cell type of the recipients (i.e., APCs and T cells, respectively) required recipient immunization with NiCl(2)/H(2)O(2). For the spread of tolerance from a given donor cell type, T cell or APC, to the homologous host cell type, the respective opposite cell type in the host was required as intermediate. We conclude that T suppressor cells and tolerogenic APCs induced by oral administration of nickel are part of a positive feedback loop that can enhance and maintain tolerance when activated by Ag associated with a danger signal. Under these conditions, APCs and T suppressor effector cells infectiously spread the tolerance to naive T cells and APCs, respectively.

T cell receptor transfection shows non-HLA-restricted recognition of nickel by CD8+ human T cells to be mediated by alphabeta T cell receptors

CD8+ T cells have been assigned a prominent role in allergic contact dermatitis, including nickel allergy; however, human nickel-reactive T cells of the CD8+ phenotype have largely escaped detailed investigation. Here we characterize two quite unusual nickel-specific cytotoxic T cell clones isolated from the peripheral blood of two nickel-sensitized patients. These clones mediate nickel-specific cytolysis of many human cell lines, independent of the expression of HLA class I, CD1, or HLA class II molecules. Lysis is mediated by the alphabeta T cell receptors and involves the perforin, but not the Fas/Fas ligand pathway. Both antigen receptors lack sequence homology to each other as well as to typical natural killer T cell receptors. A transfectant expressing the rearranged alphabeta T cell receptor derived from one of the T cell clones unequivocally demonstrates that the T cell receptor itself is necessary and sufficient to confer HLA-independent nickel specificity. The independent isolation of these clones from two individuals points to an important role of such cells in the pathology of nickel contact dermatitis.

Drug-induced autoimmunity

PURPOSE OF REVIEW

Presentation of different mechanism of drug-induced autoimmunity and highlighting of new developments.

RECENT FINDINGS

Drugs can induce autoimmune diseases by their pharmacological properties. Injection of certain drugs into the thymus can alter positive selection in the thymus and elicit autoimmune reactions. Peripheral tolerance can be broken by increasing the expression of LFA-1 adhesion molecule on T cells. This can be related to the inhibition of intracellular kinases. Alternatively, a drug specific immune response might elicit autoimmunity by cross-reactivity: the drug reactive T cells might be cross-reactive with certain peptide antigens and possibly autoantigens.

SUMMARY

Drug-specific immune responses are well described. They have a great tendency to be cross-reactive with peptide antigens. This 'immunological' cause of autoimmunity elicited by drugs may occur more frequently than thought. It connects the field of drug hypersensitivity with drug-induced autoimmunity.

A new type of metal recognition by human T cells: contact residues for peptide-independent bridging of T cell receptor and major histocompatibility complex by nickel

In spite of high frequencies of metal allergies, the structural basis for major histocompatibility complex (MHC)-restricted metal recognition is among the unanswered questions in the field of T cell activation. For the human T cell clone SE9, we have identified potential Ni contact sites in the T cell receptor (TCR) and the restricting human histocompatibility leukocyte antigen (HLA)-DR structure. The specificity of this HLA-DR-promiscuous VA22/VB17+ TCR is primarily harbored in its alpha chain. Ni reactivity is neither dependent on protein processing in antigen-presenting cells nor affected by the nature of HLA-DR-associated peptides. However, SE9 activation by Ni crucially depends on Tyr29 in CDR1alpha, an N-nucleotide-encoded Tyr94 in CDR3alpha, and a conserved His81 in the HLA-DR beta chain. These data indicate that labile, nonactivating complexes between the SE9 TCR and most HLA-DR/peptide conjugates might supply sterically optimized coordination sites for Ni ions, three of which were identified in this study. In such complexes Ni may effectively bridge the TCR alpha chain to His81 of most DR molecules. Thus, in analogy to superantigens, Ni may directly link TCR and MHC in a peptide-independent manner. However, unlike superantigens, Ni requires idiotypic, i.e., CDR3alpha-determined TCR amino acids. This new type of TCR-MHC linkage might explain the high frequency of Ni-reactive T cells in the human population.

Allelic variants of drug metabolizing enzymes as risk factors in psoriasis

The onset or exacerbation of psoriasis, a T-cell-dependent skin disease with autoimmune features, can be triggered by drugs such as antimalarials and beta-blockers. Xenobiotics may also play a role in idiopathic psoriasis. It has been hypothesized that different metabolic efficiencies caused by variant alleles of xenobiotic metabolizing enzymes could lead to the accumulation of xenobiotics or their reactive metabolites in target organs. Subsequently, neoantigens or cryptic peptides could be presented and initiate an aggressive T cell response. In this context, we analyzed a broad array of xenobiotic metabolizing enzymes in up to 327 Caucasian psoriasis patients and compared them to 235 control persons. Alleles tested include four phase I and three phase II enzymes. Significantly more carriers of the variant alleles of CYP1A1 (alleles *2A and *2C) were found in healthy controls than in patients, suggesting a protective role for these alleles. No significant difference between patients and controls could be found, however, for the other phase I alleles 1B1*1 and 1B1 *3, 2C19*1A and 2C19*2A, and 2E1*1A and 2E1*5B. Of the variant alleles coding for phase II enzymes only GSTM1, but not GSTT1 or NQOR, correlated with a risk to contract psoriasis. Some combinations of phase I and phase II enzymes suggested protective or risk-associated effects. Interestingly, heterozygosity for CYP2C19 alleles *1A and *2A was associated with increased risk for "late onset" psoriasis, whereas this genotype was protective for psoriatic arthritis. This is the first large-scale study on these enzymes and the results obtained support the concept that different activities of metabolizing enzymes can contribute to disease etiology and progression.

Heparin-induced thrombocytopenia: molecular pathogenesis

Heparin-induced thrombocytopenia (HIT) is a common and often serious complication of heparin therapy [1,2]. Although the reduction in platelet levels associated with HIT is usually not severe, about 10% of patients experience arterial and/or venous thromboses (HITT), which can be incapacitating or fatal [3]. Recent work done in our laboratory [4] and by others [5-7] has shown that patients with HIT/T* almost invariably have antibodies specific for complexes consisting of heparin and platelet factor 4 (PF4), a heparin-binding protein found normally in platelet alpha granules. We [4] and others [8] have developed hypotheses to explain how these antibodies cause HIT/T in patients given heparin, but knowledge of the disease process is far from complete. An unusual feature of HIT/T is that antibodies important in pathogenesis are specific for complexes made up of two normal body constituents: PF4 and heparin. These antibodies are produced by a high percentage of certain patient populations treated with heparin, but only a minority of antibody formers are adversely affected. We postulate that a fuller understanding of the molecular basis for this immune response could lead to improved diagnosis, treatment and prevention of HIT/T and to the identification of risk factors that predispose to this complication.

Enhanced iodination of thyroglobulin facilitates processing and presentation of a cryptic pathogenic peptide

Increased iodine intake has been associated with the development of experimental autoimmune thyroiditis (EAT), but the biological basis for this association remains poorly understood. One hypothesis has been that enhanced incorporation of iodine in thyroglobulin (Tg) promotes the generation of pathogenic T cell determinants. In this study we sought to test this by using the pathogenic nondominant A(s)-binding Tg peptides p2495 and p2694 as model Ags. SJL mice challenged with highly iodinated Tg (I-Tg) developed EAT of higher severity than Tg-primed controls, and lymph node cells (LNC) from I-Tg-primed hosts showed a higher proliferation in response to I-Tg in vitro than Tg-primed LNC reacting to Tg. Interestingly, I-Tg-primed LNC proliferated strongly in vitro against p2495, but not p2694, indicating efficient and selective priming with p2495 following processing of I-Tg in vivo. Tg-primed LNC did not respond to either peptide. Similarly, the p2495-specific, IL-2-secreting T cell hybridoma clone 5E8 was activated when I-Tg-pulsed, but not Tg-pulsed, splenocytes were used as APC, whereas the p2694-specific T cell hybridoma clone 6E10 remained unresponsive to splenic APC pulsed with Tg or I-Tg. The selective in vitro generation of p2495 was observed in macrophages or dendritic cells, but not in B cells, suggesting differential processing of I-Tg among various APC. These data demonstrate that enhanced iodination of Tg facilitates the selective processing and presentation of a cryptic pathogenic peptide in vivo or in vitro and suggest a mechanism that can at least in part account for the association of high iodine intake and the development of EAT.

Methods of in vitro toxicology

In vitro methods are common and widely used for screening and ranking chemicals, and have also been taken into account sporadically for risk assessment purposes in the case of food additives. However, the range of food-associated compounds amenable to in vitro toxicology is considered much broader, comprising not only natural ingredients, including those from food preparation, but also compounds formed endogenously after exposure, permissible/authorised chemicals including additives, residues, supplements, chemicals from processing and packaging and contaminants. A major promise of in vitro systems is to obtain mechanism-derived information that is considered pivotal for adequate risk assessment. This paper critically reviews the entire process of risk assessment by in vitro toxicology, encompassing ongoing and future developments, with major emphasis on cytotoxicity, cellular responses, toxicokinetics, modelling, metabolism, cancer-related endpoints, developmental toxicity, prediction of allergenicity, and finally, development and application of biomarkers. It describes in depth the use of in vitro methods in strategies for characterising and predicting hazards to the human. Major weaknesses and strengths of these assay systems are addressed, together with some key issues concerning major research priorities to improve hazard identification and characterisation of food-associated chemicals.

Low level lead exposure in vitro stimulates the proliferation and expansion of alloantigen-reactive CD4(high) T cells

T cells are believed to be critical functional targets of Pb immunotoxicity. In this study, low concentrations of lead (i.e., as low as 0.1 microM approximately 2 microg/dl) were found to markedly enhance the allogeneic mixed lymphocyte reaction-an assay of CD4(+) T cell responsiveness. Cell cycle analysis of cells recovered from allogeneic mixed lymphocyte cultures revealed that Pb stimulated a substantial increase in the proportion of cycling alloreactive CD4(+) T cells. The enhanced alloproliferative response was characterized by an increased population of lymphoblasts expressing heightened cell surface expression of CD4 (i.e., CD4(high) cells). Successive rounds of cell division were monitored using the cell division dye 5- (and 6)-carboxyfluorecein diacetate succinimyl ester and it was determined that the CD4(high) subpopulation comprised the expanding alloreactive T cells, which ultimately took on the phenotype of memory/effector T cells (i.e., CD44(high), CD45RB(low), CD69(high), and CD162(high)). Enhancement of T cell proliferation by lead was selective for responsiveness to alloantigen, as lead had no effect on T cell proliferation induced by mitogens or superantigen, processes that unlike alloreactivity are not dependent on antigen presentation. Collectively, these data suggest that Pb enhances alloantigen-specific T cell proliferation through an indirect mechanism involving altered antigen processing/presentation, resulting in marked clonal expansion or repertoire expansion of alloreactive T cell clones. Consistent with this suggestion was the finding that a single exposure to Pb during alloantigen priming elicited a population of CD4(+) T cells that was hyperresponsive to further alloantigen stimulation and neither lead dependent nor lead responsive.

Mercury enhances susceptibility to murine leishmaniasis

The genetic background of mice infected with Leishmania major determines the response to infection, resulting in a resistant or susceptible phenotype. Susceptible mice develop a T-helper type 2 (Th2)-type immune response following infection distinguished by the development of interleukin (IL)-4 secreting T cells in the lymph node and spleen. In SJL mice, which normally heal L. major lesions, subtoxic doses of mercury induce an autoimmune syndrome characterized by an expansion of Th2 cells. In this study, we examined the effect of mercury administration on the outcome of L. major infection in SJL mice. We show that subtoxic doses of mercuric chloride (HgCl2) exacerbate disease outcome in SJL mice resulting in increased footpad swelling and increased parasite burdens. Furthermore, the effects of HgCl2 treatment on resistance to L. major are time-dependent. The nonhealing phenotype was observed only if mice had been treated with HgCl2 prior to L. major infection for at least 1 week, a timepoint at which mice treated with HgCl2 alone had increased splenocyte IL-4 production. HgCl2 treatment also increased production of serum immunoglobulin (Ig)E and IgG1, two IL-4 dependent isotypes. These results show that HgCl2 treatment enhances the susceptibility to L. major in SJL mice, consistent with the induction of host Th2 parameters. These findings have implications for the role of mercury contamination in areas of endemic leishmaniasis.

Identification of T cells responding to a self-protein modified by an external agent

An interesting class of immune responses is that in which an environmental agent modifies a self-protein. Heparin induced thrombocytopenia (HIT) is associated with an antibody response in which the immunogen is a self-protein, platelet factor 4 (PF4), modified by an external agent, heparin. We tested the hypothesis that a T cell component exists in HIT, which like the humoral response, also requires the combination of heparin and PF4 to be activated. We identify here, a subset of T cells derived from a subject with severe HIT, which were expanded preferentially in 14-day in vitro cultures specifically in the presence of PF4:heparin complexes. A combination of T cell receptor spectratyping, CDR3 sequencing, and clonotype-specific probe hybridization were used to identify the responding T cells. The three BV17 T cell "clonotypes" thus identified had a CDR3 length of 10 amino acids, used BJ1.2, and displayed a conserved CDR3 sequence motif. These T cells are an example of a cellular response to environmentally altered self and are likely to be directly involved in HIT by functioning as T helper cells. The results are discussed in terms of the possible role of modification of antigen presentation by the external agent in this response.

Proteolytic cleavage of a self-antigen following xenobiotic-induced cell death produces a fragment with novel immunogenic properties

The heavy metal mercury elicits a genetically restricted autoantibody response in mice that targets the nucleolar autoantigen fibrillarin. HgCl2-induced cell death of macrophages resulted in the proteolytic cleavage of fibrillarin. A prominent feature of mercury-induced cell death was the generation of a 19-kDa fragment of fibrillarin that was not found following apoptotic or nonapoptotic cell death induced by stimuli other than mercury. Proteolysis of fibrillarin lacking cysteines, and therefore unable to bind mercury, also produced the 19-kDa fragment, suggesting that a mercury-fibrillarin interaction was not necessary for the unique cleavage pattern of this self-Ag. In contrast to immunization with full-length fibrillarin, the 19-kDa fragment produced anti-fibrillarin Abs with some of the properties of the HgCl2-induced anti-fibrillarin response. We propose that cell death following exposure to an autoimmunity-inducing xenobiotic can lead to the generation of novel protein fragments that may serve as sources of antigenic determinants for self-reactive T lymphocytes.

Can drugs cause autoimmune thrombocytopenic purpura?

A wide range of medications can cause life-threatening immune thrombocytopenia (ITP), hemolytic anemia, or neutropenia in sensitive individuals. The antibodies associated with these conditions usually require soluble drug to be present in order to react with the cell membrane glycoproteins for which they are specific. However, some patients make drug-independent antibodies (autoantibodies) as well. Occasionally, only autoantibodies are produced following exposure to a drug. Although drugs and other small molecules can become conjugated to proteins in vivo, which may induce an immune response, only fragmentary information is available to explain how exogenous substances sometimes perturb the immune system in such a way that antibodies capable of causing immune cytopenia are produced. Platelets are affected by drug-induced antibodies more often than any other blood element. For many drug-induced thrombocytopenias, the targeted membrane glycoproteins are readily accessible for laboratory investigation and methods for detecting the responsible antibodies are well developed. Techniques for studying cellular aspects of the immune response induced by drugs through in vitro manipulation of T and B lymphocytes are also advancing rapidly. Studies of drug-induced ITP may provide clues to the general mechanisms whereby drugs and other xenobiotics induce immune diseases. Clinicians should consider the possibility of an exogenous trigger in patients who present with apparent autoimmune thrombocytopenia.

Polymorphisms of the xenobiotic-metabolizing enzymes CYP1A1 and NAT-2 in systemic sclerosis and lupus erythematosus

The etiology of systemic autoimmune diseases, such as systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) is still unknown. In several cases, however, xenobiotics (i.e. drugs and occupational agents) were identified as etiologic agents and associations with certain polymorphic alleles of xenobiotic-metabolizing enzymes have been reported. Cytochrome P4501A1 (CYP1A1) and N-acetyltransferase 2 (NAT-2) are xenobiotic-metabolizing enzymes of phase 1- and phase 2-metabolism, respectively. CYP1A1 may activate drugs and other chemicals to reactive metabolites. NAT-2 is the most important enzyme in acetylation of aromatic amines, and thus may be responsible for detoxification of many of these compounds. Two polymorphisms of the human CYP1A1 gene, a point mutation in the 3' flanking region of the gene (Msp1) and a mutation in exon 7 leading to an isoleucine-valine-exchange in the heme-binding region of the enzyme, have been described and may lead to a higher basal and inducible enzyme activity. With respect to NAT-2, several alleles which combine for the two phenotypes "fast" and "slow" acetylators have been described. We analyzed the gene frequencies of the CYP1A1 polymorphisms and the phenotypes of NAT-2 in patients suffering from idiopathic SLE or SSc. CYP1A1 polymorphisms were analyzed in genomic DNA by PCR, whereas NAT-2 phenotypes were measured by the caffeine method. For CYP1A1 polymorphisms, 106 patients have been typed until now. The SLE group (n = 68) exhibited a significant increase (p < 0.05) in the mutant Val-allele (OR = 2.59) when compared to controls (n = 184). However, no significant differences in allele frequencies for MspI in the SLE group and for both CYP1A1 polymorphisms in the SSc group could be observed. Regarding the NAT-2 phenotype, patients suffering from SLE (n = 88) 75% and SSc (n = 26) 80.2%, respectively, were slow acetylators compared to 55% slow acetylators in the healthy German population (p < 0.05). The observed increased frequencies of the CYP1A1 mutant Val-allele and the slow actylator phenotype in idiopathic autoimmune disease support our concept that in slow acetylators non-acetylated xenobiotics may accumulate and are subsequently metabolized by other enzymes into reactive intermediates. Thus, enhanced formation of reactive metabolites could alter self-proteins presented to the immune system thus stimulating autoreactive T cells which induce autoimmunity.

T-cell recognition of lipid peroxidation products breaks tolerance to self proteins

Peroxidation of polyunsaturated fatty acids in lipoproteins and cell membrane phospholipids occurs in many situations in the body, both under normal and pathological conditions. Low-density lipoprotein is particularly prone to oxidation and is believed to be a pathogenetic component in atherogenesis. Both antibody responses and T-cell responses to oxidatively modified lipoproteins have been demonstrated in humans as well as in animal models. However, little is known about how these responses arise or how T cells recognize these antigens. In the present study, mice were immunized with homologous albumin covalently modified with a series of defined aldehydes which are known to be generated during lipid peroxidation. T-cell hybridomas from immunized animals demonstrated major histocompatibility complex-restricted and protein sequence-dependent responses to modified albumin, but not to native albumin. In addition to the response to modified epitopes, some aldehyde modifications resulted in strong antibody responses also to the non-modified protein. This T-cell-dependent break of tolerance constitutes a novel pathway for induction of autoimmunity by lipid peroxidation. The findings have implications in many situations where lipid peroxidation products are generated, including atherosclerosis and inflammatory and infectious diseases.

Murine mercury-induced autoimmunity: a model of chemically related autoimmunity in humans

Human exposure to certain compounds or therapeutic drugs can result in the development of an autoimmune syndrome. Mercury (Hg) induced autoimmunity is one of the few animal models in which administration of a chemical induces a specific loss of tolerance to self-antigens. After receiving subtoxic doses of Hg or other heavy metals, susceptible mouse strains rapidly develop highly specific antibodies to nucleolar antigens. In addition, these animals display a general activation of the immune system, especially pronounced for the Th2 subset and a transient glomerulonephritis with immunoglobulin deposits. Like many human autoimmune diseases, this syndrome is associated with the expression of susceptible major histocompatibility complex (MHC) class II genes. In this article, we review the essential features of this model, and we discuss the putative mechanisms by which Hg creates such a severe immune dysfunction.

Nickel Allergy in Mice: Enhanced Sensitization Capacity of Nickel at Higher Oxidation States

Attempts to induce contact hypersensitivity to nickel in mice using, e.g., Ni(II)Cl2 often failed. Here, we report that sensitization was achieved by injecting Ni(II)Cl2 in combination with either CFA or an irritant, such as SDS and PMA, or IL-12, or by administering nickel at higher oxidation states, i.e., Ni(III) and Ni(IV). Although Ni(II), given alone, was ineffective in T cell priming, it sufficed for eliciting recall responses in vivo and in vitro, suggesting that Ni(II) is able to provide an effective signal 1 for T cell activation, but is unable to provide an adequate signal 2 for priming. Immunization of mice with nickel-binding proteins pretreated with Ni(IV), but not with Ni(II), allowed them to generate nickel-specific CD4+ T cell hybridomas. Ni(II) sufficed for restimulation of T cell hybridomas; in this and other aspects as well, the hybridomas resembled the nickel-specific human T cell clones reported in the literature. Interestingly, restimulation of hybridomas did not require the original Ni(IV)-protein complex used for priming, suggesting either that the nickel ions underwent ligand exchange toward unknown self proteins or peptides or that nickel recognition by the TCR is carrier-independent. In conclusion, we found that Ni(III) and Ni(IV), but not Ni(II) alone, were able to sensitize naive T cells. Since both Ni(III) and Ni(IV) can be generated from Ni(II) by reactive oxygen species, released during inflammation, our findings might explain why in humans nickel contact dermatitis develops much more readily in irritated than in normal skin.

Complexes of Heparin and Platelet Factor 4 Specifically Stimulate T Cells From Patients With Heparin-Induced Thrombocytopenia/Thrombosis

Heparin-induced thrombocytopenia with thrombosis (HITT) is associated with antibodies specific for complexes consisting of heparin and platelet factor 4 (PF4). Studies in individual patients with HITT have demonstrated immunoglobulin (Ig) class switching from IgM to the IgG or IgA isotypes. This transition is thought to require helper T cells, but no studies of the cellular or molecular basis of this process have yet been reported. To characterize T-cell involvement in HITT, peripheral blood mononuclear cells (PBMC) from two patients with classical HITT obtained shortly after the acute episode were restimulated with heparin:PF4 complexes, PF4 alone, heparin alone, and medium alone in the presence of autologous antigen-presenting cells (APC). Responding T cells were then examined using the technique of “spectratyping,” in which sequences encoding CDR3 domains of individual V beta (BV) families are amplified and separated by gel electrophoresis. After 14 days in culture with antigen (heparin:PF4 complexes), but not after culture with PF4, heparin, or medium alone, patient cells, but not cells from normal subjects, preferentially expressed T-cell receptor (TCR)-containing β chains of the BV 5.1 family. Nucleotide sequencing of BV 5.1 TCR CDR3 showed that each patient had a personal repertoire, but also shared a tetrapeptide motif (PGTG). These findings provide evidence that the humoral immune response associated with HITT is driven by helper T cells that presumably recognize peptides derived from PF4. Identification of a common β-chain CDR3 motif in responding T cells from each of two patients suggests that a limited number of helper TCRs may be used to mount an antibody response to heparin:PF4 complexes. TCR spectratyping appears to offer a new way to examine the molecular basis of pathologic immune responses and may be useful in further studies of HITT and other immune-mediated hematologic disorders.

Biochemical characteristics of Eiseniapore, a pore-forming protein in the coelomic fluid of earthworms

The cytolytic protein Eiseniapore (38 kDa) from coelomic fluid of the earthworm Eisenia fetida functionally requires sphingomyelin as revealed by using mammalian erythrocytes and phospholipid vesicles. The effects of ions, glycoproteins and phospholipids were investigated for the two-step Eiseniapore action mode, binding and pore formation in different assays. Eiseniapore lysis is activated by thiol groups but inhibited by metal ions. Eiseniapore binding to target membranes is inhibited by Eiseniapore-regulating factor, vitronectin, heparin and lysophosphatidylcholine. Ca2+ and Mg2+ were found to be not necessary for membrane binding or lytic activity. Sphingomyelin was essential for Eiseniapore-induced leakage of liposomes. We describe a cytolytic protein/toxin in Eiseniapore which differs from the established classification; it can be activated by thiol groups and is inhibited by sphingomyelin. Electron microscopy of erythrocyte membranes confirmed ring-shaped structures (pores) with a central channel with outer (10 nm) and inner (3 nm) diameters as shown previously [Lange, S., Nüssler, F., Kauschke, E., Lutsch, G., Cooper, E.L. & Herrmann, A. (1997) J. Biol. Chem. 272, 20 884-20 892] using artificial membranes. Functional evidence of pore formation by Eiseniapore was revealed as protection of lysis by carbohydrates occurred at an effective diameter above 3 nm. From these results, we suggest a plausible explanation for the mechanism by which components of the earthworm's immune system destroy non-self components.

T cell cross-reactivity to heavy metals: identical cryptic peptides may be presented from protein exposed to different metals

The mechanisms by which metals induce activation of T cells and thus produce allergic and/ or autoimmune reactions are still obscure, and the same is true for the mechanisms that underly T cell cross-reactivity to different heavy metal ions. In the present study, we investigated induction by metals of T cell reactions to cryptic peptides of bovine RNase A. Murine CD4+ T cell hybridomas specific for cryptic RNase peptides presented from Au(III)-treated RNase were used as detection probes. We showed that in vitro treatment of RNase with Pd(II), Pd(IV), Ni(IV), and partially Pt(IV), but not Au(I), Ni(II), or Pt(II), induced presentation of the same cryptic peptides as those presented from Au(III)-treated RNase. That the former heavy metal ions, but not the latter, were able to alter the antigenicity of RNase was reflected by their ability to induce conformational changes of RNase, as detected by circular dichroism spectroscopy. Furthermore, upon immunization against RNase pretreated with these metals, CD4+ T cell hybridomas specific for unidentified cryptic peptides were obtained. In conclusion, "metal-specific" T cell reactions may be directed against cryptic peptides, and metal cross-reactivity in allergic individuals might be due to metal-induced presentation of overlapping, but not identical, panels of cryptic peptides.

Selective immunomodulation by the autoimmunity-inducing xenobiotics streptozotocin and HgCl2

Exposure to certain drugs and environmental chemicals can provoke the onset of autoimmune disease in susceptible individuals by releasing (self) epitopes for which tolerance has not been established, while simultaneously providing the necessary adjuvant activity. The resulting response type is influenced by the genotype of exposed individuals and relates to susceptibility to the adverse immune effects of the chemicals. Here, we assessed the modulatory role of the chemical compounds themselves. A single injection of streptozotocin (STZ) increased the number of CD8+ cells, macrophages, apoptotic cells, and IFN-gamma-producing T helper and T cytotoxic cells, whereas the number of CD4+ cells and B cells was reduced in the draining lymph node. Coinjection with the reporter antigen TNP-OVA resulted in primary and secondary production of TNP-specific antibodies that were predominantly of IgG2a and IgG2b isotype, whereas STZ did not enhance priming for delayed-type hypersensitivity (DTH) responses to TNP-OVA. Injection of HgCl2 on the other hand, reduced the number of IFN-gamma-producing cells, induced accumulation of B cells and CD4+ and CD8+ T cells, enhanced IgG1 and IgE production to TNP-OVA, and primed for secondary IgG1 and IgE production as well as for DTH reactions. Together these results indicate that a single injection of STZ stimulates type-1 responses, whereas HgCl2 enhanced mixed type-1 and -2 responses in BALB/c mice. These response types match the (auto)immune effects elicited to unknown (auto)antigens following multiple injections of these chemicals.

Direct, MHC-dependent presentation of the drug sulfamethoxazole to human alphabeta T cell clones

T cells can recognize small molecular compounds like drugs. It is thought that covalent binding to MHC bound peptides is required for such a hapten stimulation. Sulfamethoxazole, like most drugs, is not chemically reactive per se, but is thought to gain the ability to covalently bind to proteins after intracellular drug metabolism. The purpose of this study was to investigate how sulfamethoxazole is presented in an immunogenic form to sulfamethoxazole-specific T cell clones. The stimulation of four CD4(+) and two CD8(+) sulfamethoxazole-specific T cell clones by different antigen-presenting cells (APC) was measured both by proliferation and cytolytic assays. The MHC restriction was evaluated, first, by inhibition using anti-class I and anti-class II mAb, and second, by the degree of sulfamethoxazole-induced stimulation by partially matched APC. Fixation of APC was performed with glutaraldehyde 0.05%. The clones were specific for sulfamethoxazole without cross-reaction to other sulfonamides. The continuous presence of sulfamethoxazole was required during the assay period since pulsing of the APC was not sufficient to induce proliferation or cytotoxicity. Stimulation of clones required the addition of MHC compatible APC. The APC could be fixed without impairing their ability to present sulfamethoxazole. Sulfamethoxazole can be presented in an unstable, but MHC-restricted fashion, which is independent of processing. These features are best explained by a direct, noncovalent binding of sulfamethoxazole to the MHC-peptide complex.