Selective requirement for CD40-CD154 in drug-induced type 1 versus type 2 responses to trinitrophenyl-ovalbumin

CD40-CD154: A perspective from type 2 immunity

The interaction between CD40 and CD154 (CD40 ligand) is central in immunology, participating in CD4⁺ T cell priming by dendritic cells (DC), CD4⁺ T cell help to B cells and classical macrophage activation by CD4⁺ T cells. However, its role in the Th2 side of immunology including helminth infection remains incompletely understood. Contrary to viral and bacterial stimuli, helminth products usually do not cause CD40 up-regulation in DC, and exogenous CD40 ligation drives Th2-biased systems towards Th1. On the other hand, CD40 and CD154 are necessary for induction of most Th2 responses. We attempt to reconcile these observations, mainly by proposing that (i) CD40 up-regulation in DC in Th2 systems is mostly induced by alarmins, (ii) the Th2 to Th1 shift induced by exogenous CD40 ligation is related to the capacity of such ligation to enhance IL-12 production by myeloid cells, and (iii) signals elicited by endogenous CD154 available in Th2 contexts and by exogenous CD40 ligation are probably different. We stress that CD40-CD154 is important beyond cognate cellular interactions. In such a context, we argue that the proliferation response of B-cells to IL-4 plus CD154 reflects a Th2-specific mechanism for polyclonal B-cell amplification and IgE production at infection sites. Finally, we argue that CD154 is a general immune activation signal across immune polarization including Th2, and propose that competition for CD154 at tissue sites may provide negative feedback on response induction at each site.

Structure-activity differences of chlorogenic acid and its isomers on sensitization via intravenous exposure

Chlorogenic acid (CGA) is found in many plants that are used as medicinal substances in traditional Chinese medicine injectables (TCMIs). However, to date, there is controversy as to whether CGA is the major cause of TCMIs-related hypersensitivity administered intravenously. Therefore, the aim of this study was to evaluate the potential sensitization of CGA and structure-activity differences between its isomers using an intravenous exposure mouse model. The results showed that popliteal lymph nodes proliferation was significantly induced by CGA and its isomers. Both CGA and isochlorogenic acid A (iso-CGA A) significantly enhanced the secretion of trinitrophenyl (TNP) ovalbumin-specific immunoglobulin (Ig)G1; and iso-CGA B significantly induced TNP-specific IgG1, IgM, and IgG2b secreting. Furthermore, the results of quantitative structure-activity relationship analysis suggested that chemical structure factors, including atomic mass, electronegativity, atom shape and size, atom distribution, atomic weight, and atomic polarizabilities, the ionic currents, were significantly correlated with the potential sensitization of CGA and its isomers. In summary, when administered intravenously, the strength and type of sensitization may be correlated with structure differences in the CGA family.

An intravenous exposure mouse model for prediction of potential drug-sensitization using reporter antigens popliteal lymph node assay

Immune-mediated drug hypersensitivity is a particularly concerning health-safety issue among clinicians given its unpredictability and potentially life-threatening effects, especially with exposure to intravenous drugs. Therefore, the development of intravenous drug-exposure models for drug-hazard assessments has garnered increasing interest in recent years. In this study, we used reporter antigens popliteal lymph node assay to investigate the potential value of intravenous exposure to a selected variety of allergenic compounds, including ovalbumin (OVA), concanavalin A (ConA) and diclofenac. The trinitrophenyl (TNP)-specific antibody-forming cells were used to assess the systemic immune responses to a bystander antigen. Mice were subsequently sensitized by TNP-OVA, and then intravenous exposure to one of the selective compounds. As expected, all positive compounds induced significant popliteal lymph node (PLN) proliferation compared with the control. OVA significantly increased Cluster of Differentiation 4 receptors (CD⁴)⁺ interleukin-4 (IL-4)⁺ T-helper 2 (Th2) cells and, consequently, increased the ratios of IL-4/interferon-γ (IFN-γ) antibody-forming cells (AFCs) in PLNs, while bringing about a dose-dependent increase in immunoglobulin G1 (IgG1) AFCs; these findings indicate that a Th2 hypersensitivity response was induced. A Th2 response was also observed in diclofenac sodium-treated groups, and for ConA, a more mixed Th1/Th2 immune response appeared to be induced. In addition, there was no marked reaction with the negative compound. Together, it seems likely that the intravenous exposure model may be useful for drug-induced systemic hypersensitivity assessments.

Lack of evidence of CD40 ligand involvement in transfusion-related acute lung injury

Activated platelets have been implicated in playing a major role in transfusion-related acute lung injury (TRALI), as platelets can trigger neutrophils, resulting in vascular damage. We hypothesized that binding of platelet CD40 ligand (CD40L) to endothelial CD40 is essential in the onset of TRALI. Mice were challenged with monoclonal major histocompatibility complex (MHC)-1 antibody which induced TRALI, evidenced by pulmonary oedema, accompanied by significantly elevated bronchoalveolar fluid (BALF) levels of total protein and elevated plasma levels of keratinocyte-derived chemokine (KC) and macrophage inflammatory protein-2 (MIP-2) compared to infusion of isotype antibody (all Ps < 0·05). Treatment with ciglitazone, which inhibits platelet CD40L expression, had no effect on pulmonary and systemic inflammation compared to controls. In addition, treatment with anti-CD40L antibody, which antagonizes all CD40-CD40L interactions, also did not abrogate the TRALI reaction. Furthermore, levels of soluble CD40L were measured in a cohort of cardiac surgery patients, who were followed prospectively for the onset of TRALI after transfusion. Plasma levels of sCD40L at baseline and at time of developing TRALI did not differ between TRALI patients and controls (transfused cardiac surgery patients not developing acute lung injury) (275 ± 192 versus 258 ± 346 and 93 ± 82 versus 93 ± 123 pg/ml, respectively, not significant). In conclusion, these results do not support the idea that the CD40-CD40L interaction is involved in mediating TRALI.

An in vivo tiered approach to test immunosensitization by low molecular weight compounds

New chemical entities are tested in general toxicity assays during development before entering clinical trials. However, immunosensitization of these entities is not tested on a standard basis. There are no in vitro or in vivo standardized methods available for testing immunosensitization or immunostimulation. In this chapter, we describe a tiered strategy oral exposure model for assessing immunosensitization or immunostimulation capacity of low molecular weight compounds. The strategy starts from a set of data that may provide information on bioactivation, conjugation (hapten-protein conjugate formation), cytotoxicity and signs of inflammation in any of the animals in a 28 day-toxicity study. In case of concern, a reporter antigen-popliteal lymph node assay (RA-PLNA) and, subsequently, an oral exposure experiment with the reporter antigen can be performed. Based on the presence of RA-specific immune responses an indication for immunosensitization can be found.

Uncoupling of induced protein processing from maturation in dendritic cells exposed to a highly antigenic preparation from a helminth parasite

TLR ligands induce dendritic cell (DC) maturation. During this process, cells initiate proteolytic degradation of internalized protein Ags into peptides that complex with MHC class II (MHC II) and simultaneously increase expression of costimulatory molecules and of cytokines such as IL-6, IL-12, and IL-23. In these ways, TLR-activated DCs are able to activate naive Th cells and initiate Th1 and Th17 responses, and TLR ligands thus serve as adjuvants for these types of responses. In contrast, products from helminth parasites generally do not activate DCs and act as adjuvants for Th2 response induction. We have explored the underlying basis for this form of adjuvanticity. We show that exposure of DCs to soluble Ags from the eggs of the helminth parasite Schistosoma mansoni (schistosome egg Ag (SEA)) leads to the induction of proteolysis of internalized Ag. This occurs in the absence of significant induction of costimulatory molecule expression or production of proinflammatory cytokines. SEA-induced Ag processing occurs independently of MyD88 or Toll/IL-1 receptor domain containing adaptor inducing IFN-beta (Trif), but is significantly attenuated by inhibition of p38, but not ERK, signaling. In DCs exposed to SEA, ligation of CD40 provides a necessary second signal that stimulates costimulatory molecule expression, allowing DCs to mature into capable APCs. Collectively, the data demonstrate the existence of a MyD88/Trif-independent, p38-dependent pathway of Ag processing in DCs, which is uncoupled from conventional DC maturation and is associated with induction of Th2-type immune responses.

Sulfamethoxazole and its metabolite nitroso sulfamethoxazole stimulate dendritic cell costimulatory signaling

Different signals in addition to the antigenic signal are required to initiate an immunological reaction. In the context of sulfamethoxazole allergy, the Ag is thought to be derived from its toxic nitroso metabolite, but little is known about the costimulatory signals, including those associated with dendritic cell maturation. In this study, we demonstrate increased CD40 expression, but not CD80, CD83, or CD86, with dendritic cell surfaces exposed to sulfamethoxazole (250-500 microM) and the protein-reactive metabolite nitroso sulfamethoxazole (1-10 microM). Increased CD40 expression was not associated with apoptosis or necrosis, or glutathione depletion. Covalently modified intracellular proteins were detected when sulfamethoxazole was incubated with dendritic cells. Importantly, the enzyme inhibitor 1-aminobenzotriazole prevented the increase in CD40 expression with sulfamethoxazole, but not with nitroso sulfamethoxazole or LPS. The enzymes CYP2C9, CYP2C8, and myeloperoxidase catalyzed the conversion of sulfamethoxazole to sulfamethoxazole hydroxylamine. Myeloperoxidase was expressed at high levels in dendritic cells. Nitroso sulfamethoxazole immunogenicity was inhibited in mice with a blocking anti-CD40L Ab. In addition, when a primary nitroso sulfamethoxazole-specific T cell response using drug-naive human cells was generated, the magnitude of the response was enhanced when cultures were exposed to a stimulatory anti-CD40 Ab. Finally, increased CD40 expression was 5-fold higher on nitroso sulfamethoxazole-treated dendritic cells from an HIV-positive allergic patient compared with volunteers. These data provide evidence of a link between localized metabolism, dendritic cell activation, and drug immunogenicity.

Immunological principles of T-cell-mediated adverse drug reactions in skin

Drug hypersensitivity reactions in skin are an immune-mediated phenomenon associated with significant patient mortality and morbidity. Antigen-specific T cells, which have been isolated from the peripheral circulation and target organs of hypersensitive patients, are thought to propagate and regulate the development of clinical symptoms. The investigation of clinical cases with respect to the basic cellular and chemical mechanisms that underpin drug hypersensitivity has resulted in: i) the need to redress some aspects of present immunological dogma; and ii) additional fundamental immunological questions. Thus, the aim of this review article is to summarise present opinion on how and why drugs initiate a pathogenic T-cell response in a small section of the population and subsequently reflect on gaps in basic immunology and where future research might lead.

Detection of autoimmunity by pharmaceuticals

Despite the important health and economic impact of autoimmunogenicity or allergenicity by pharmaceuticals models to detect such adverse effects are not available yet. The most important reason for this is the related complex interplay of multiple factors, for which reason these adverse effects are also referred to as idiosyncratic in nature. Moreover, clinical effects are quite diverse, and involve both organ-specific and systemic effects, including a diversity of skin diseases. Because of its complexity on the one hand and the fundamental knowledge on certain particular mechanistic effects it may be more relevant to design a rationalistic toolbox of test models from which a predictive strategy can be composed. Since one mechanistic aspect centers around T cell sensitization a straightforward lymph node assay such as the reporter antigen-popliteal lymph node assay (RA-PLNA) would fit in such a toolbox. This RA-PLNA holds a strong promise to distinguish sensitizing and/or neoantigen-forming capacity of low molecular weight pharmaceuticals. In addition, from the pharmacokinetic point of view a rationalistic toolbox should also contain oral exposure models with immunological read out parameters in normal or in genetically predisposed animal strains. This review focuses on these two categories of candidate test methods, PLNA and oral exposure models, and proposes to use these in tandem in order to predict the hazard of induction of allergy or autoimmune phenomena by new pharmaceutical candidates.

The reporter antigen popliteal lymph node assay

Many chemicals, including drugs and environmental pollutants, may have the intrinsic capacity to stimulate or dysregulate immune responses. These responses may create considerable problems for exposed subjects in terms of development of autoimmunity or hypersensitivity reactions. The popliteal lymph node assay (PLNA) provides a suitable tool to assess the immunostimulating potential of chemicals and might be a potential candidate as a screening tool in immunotoxicological hazard identification. The use of so-called reporter antigens (RA) in this assay additionally enables differentiation between immunosensitizing (sensitizers), immunostimulating (irritants), and innocent chemicals. In the RA-PLNA, the compound of interest is injected into the hind footpad together with a nonsensitizing dose of the RA. After 6 to 8 days, RA-specific responses are monitored in the draining PLN by measuring RA-specific antibody formation, cytokine secretion, and shifts in immune cell numbers. Hence, this simple and straightforward assay provides immunologically relevant information about the immunomodulating properties of a chemical.

Immune Modulation by Cadmium and Lead in the Acute Reporter Antigen–Popliteal Lymph Node Assay

Immune modulation by heavy metals may cause serious adverse health effects in humans, although the mechanisms involved are not well understood. Both cadmium and lead are important environmental and occupational toxins. Therefore, in the current study, the costimulatory/adjuvant effects and the T-cell-activating potential of these metals (i.e., CdCl2 and PbCl2), are examined. These immune-modulating properties are critical in the development of conditions such as allergy, hypersensitivity, and autoimmunity. Using the direct popliteal lymph node assay (PLNA) and reporter antigen-popliteal lymph node assay (RA-PLNA) both metals were examined individually for immunotoxicity. Mercury (i.e., HgCl2) was included for comparative purposes as its effects in the RA-PLNA are well documented. Seven days following a single footpad injection containing metal and/or RA (trinitrophenyl-ovalbumin [TNP-OVA] or TNP-Ficoll), BALB/c mice were sacrificed and the popliteal lymph nodes (PLNs) removed. PLN cellularity, TNP-specific antibody-secreting cells (ASCs), and lymphocyte subsets were assessed. All three metals strongly stimulated T- and B-cell proliferation and ASC production following coinjection with the RA TNP-OVA. In each case, ASC production was skewed towards the IgG1 isotype. In addition, all three metals induced IgG production to TNP-Ficoll (although relatively weakly in the case of Cd). These results show that each of these metals can provide adjuvant signals to promote lymphocyte proliferation and enhance adaptive immune responses to unrelated antigens. Skewing of immune responses towards T helper type 2 responses suggests that each of these metals can enhance allergic and hypersensitivity reactions to environmental antigens. Furthermore, the induction of IgG responses to TNP-Ficoll, a T-cell-independent antigen, indicates that each of these metals can activate neoantigen-specific T cells. T-cell activation by metals can lead to metal hypersensitivity and has been implicated in the development of autoimmunity. This is the first report of immune modulation by CdCl2 and PbCl2 in the RA-PLNA.

Differential Requirement for CD28/CTLA-4-CD80/CD86 Interactions in Drug-Induced Type 1 and Type 2 Immune Responses to Trinitrophenyl-Ovalbumin

The use of mAbs to abrogate costimulatory interactions has attracted much attention with regard to prevention and modulation of adverse (auto)immune-like reactions. However, the role of costimulatory molecules and possible therapeutic use of Ab-treatment in drug-induced immunostimulation is poorly elucidated. In the present studies, we show that CD28/CTLA-4-CD80/CD86 costimulatory interactions differently regulate drug-induced type 1 and type 2 responses to an identical bystander Ag, TNP-OVA, in BALB/c mice using the reporter Ag popliteal lymph node assay. The antirheumatic drug D-Penicillamine, which may induce lupus-like side-effects, stimulated type 2 responses against TNP-OVA, characterized by the production of IL-4 and TNP-specific IgG1 and IgE. These responses were abrogated in CD80/CD86-deficient mice and in wild-type mice that were treated with anti-CD80 and anti-CD86, or CTLA-4-Ig. Anti-CTLA-4 intensively enhanced the D-Penicillamine-induced effects. In contrast, the type 1 response (IFN-gamma, TNF-alpha, IgG2a) to TNP-OVA induced by the diabetogen streptozotocin still developed in the absence of CD80/CD86 costimulatory signaling. In addition, it was demonstrated that coadministration of anti-CD80 and anti-CD86 mAbs slightly enhanced streptozotocin-induced type 1 responses, whereas the CTLA-4-Ig fusion protein completely abrogated this response. In conclusion, different drugs may stimulate distinct types of immune responses against an identical bystander Ag, which are completely dependent on (type 2) or independent of (type 1) the CD28/CTLA-4-CD80/CD86 pathway. Importantly, the effects of treatment with anti-CD80/CD86 mAbs and CTLA-4-Ig may be considerably different in responses induced by distinct drugs.

Selective haptenation of cellular or extracellular protein by chemical allergens: association with cytokine polarization

Sensitizing chemicals can cause different forms of allergy, allergic contact dermatitis, or sensitization of the respiratory tract. These discrete types of chemicals induce in mice qualitatively divergent immune responses; contact allergens provoke preferential type 1 responses, whereas respiratory allergens stimulate selective type 2 responses. We have questioned whether the ability of chemicals to initiate polarized immune responses is in part a function of the nature of their association with protein. Cytokine secretion profiles provoked following topical exposure of BALB/c mice to dinitrochlorobenzene (DNCB), dinitrofluorobenzene (DNFB), fluorescein isothiocyanate (FITC), trimellitic anhydride (TMA), and dinitrobenzenesulfonyl chloride (DNBSCl) were compared with the distribution of covalent binding to U937 cells and/or to serum proteins in vitro. DNCB and DNFB each provoked a type 1 cytokine secretion profile, with high levels of IFN-gamma, but relatively low levels of type 2 cytokines IL-4, -5, and -10. The converse selective type 2 phenotype was seen following equivalent exposure to TMA, FITC, or DNBSCl. Each chemical bound covalently to U937 cells and to serum proteins, when incubated with cells or serum alone. When incubated with cells and serum together, DNCB and DNFB bound selectively to cellular protein, whereas TMA, FITC, and DNBSCl bound selectively to serum. These investigations show that the distribution of antigen formation of chemical allergens in an in vitro model system segregates with the type of cytokines secreted from activated lymph node cells in an in vivo mouse model. Chemical allergens that stimulate type 1 cytokine secretion profiles bind selectively to cellular proteins, whereas others that provoke type 2 cytokine profiles bind preferentially to serum proteins.

Murine models of drug hypersensitivity

PURPOSE OF REVIEW

Drug hypersensitivity reactions are relatively rare but may result in severe morbidity and fatalities. Due to the idiosyncratic nature and multifactorial etiology of these reactions, development of a single animal model to study the immunosensitizing mechanisms of all drugs is impossible. This hampers the development of predictive screening models that are urgently needed to assess the immunostimulating capacity of newly developed drugs. The present review will focus on recent findings on mechanisms of drug hypersensitivity reactions obtained with murine models, and on the use of these models as potential screening tools to assess the immunostimulating capacity of drugs.

RECENT FINDINGS

Mechanisms of drug-induced sensitization versus tolerance appear dependent on generally accepted immunological paradigms. For instance, co-stimulatory signaling by antigen-presenting cells is decisive in drug-induced immunosensitization and both T cells and antigen-presenting cells are important for the induction of tolerance to orally administered drugs. From recent studies it has been hypothesized that expression of stress-associated transcription factors and the expression of costimulatory molecules or cytokine production within hours or days after the initial exposure may be representative of drug-induced hypersensitivity reactions and may thus be used as predictive parameters to screen for immunosensitizing drugs.

SUMMARY

The development of animal models to study mechanisms of drug hypersensitivity reactions is still in its infancy. Much effort has been made, however, to search for early indicators of immunostimulation in murine animal models that may eventually appear useful in a tiered strategy to assess drug-induced sensitization.

The effect of the food matrix on in vivo immune responses to purified peanut allergens

There is little knowledge about the factors that determine the allergenicity of food proteins. One aspect that remains to be elucidated is the effect of the food matrix on immune responses to food proteins. To study the intrinsic immunogenicity of allergens and the influence of the food matrix, purified peanut allergens (Ara h 1, Ara h 2, Ara h 3, or Ara h 6) and a whole peanut extract (PE) were tested in the popliteal lymph node assay (PLNA) and in an oral model of peanut hypersensitivity. In the PLNA, peanut proteins were injected into the hind footpad of BALB/c mice; in the oral exposure experiments C3H/HeOuJ mice were gavaged weekly with PE or allergens in the presence of cholera toxin (CT). Upon footpad injection, none of the allergens induced significant immune activation. In contrast, PE induced an increase in cell number, cytokine production, and activation of antigen-presenting cells. Furthermore, the presence of a food matrix enhanced the immune response to the individual allergens. Oral exposure to the purified allergens in the presence of CT induced specific IgE responses, irrespective of the presence of a food matrix. These results suggest that purified peanut allergens possess little intrinsic immune-stimulating capacity in contrast to a whole PE. Moreover, the data indicate that the food matrix can influence responses to individual proteins and, therefore, the food matrix must be taken into account when developing models for allergenic potential assessment.

The Reactive d-Glucopyranose Moiety of Streptozotocin Is Responsible for Activation of Macrophages and Subsequent Stimulation of CD8+ T Cells

The antitumor drug streptozotocin (STZ) is commonly used as a diabetogenic compound in animal models. At relatively low doses, STZ-induced beta cell destruction is associated with Th1-driven type 1 immune reactions, including macrophages (MPhi) and IFN-gamma-producing CD8(+) T cells. STZ induces similar Th1-dependent effects in the popliteal lymph node assay (PLNA), and because this assay allows straightforward examination of early immunostimulating processes, the PLNA was used to further examine the importance of MPhi and structural properties of STZ in relation to the induction of type 1 immune responses. Results show that elimination of MPhi with clodronate-containing liposomes prior to exposure to STZ prevents the occurrence of some (CD8(+) T cell activation, IFN-gamma production, and tissue destruction) but not all (IgG2a formation) type 1 immune responses. It appeared that stimulation of MPhi depends on the d-glucopyranose moiety of STZ, as well as on the intact reactive N-methyl-N-nitrosourea (MNU) moiety. However, the MNU moiety suffices to induce IgG2a formation. In addition, STZ-derived nitric oxide may have modulating effects on the elicitation of STZ-induced immune responses. Present results support the idea that MPhi activation is indispensable for the STZ-induced tissue destructive type 1 responses and that various STZ-induced type 1 immune responses are differently regulated.

Investigating the Role of 2-Phenylpropenal in Felbamate-Induced Idiosyncratic Drug Reactions

Felbamate (2-phenyl-1,3-propanediol dicarbamate, FBM) can cause aplastic anemia and hepatotoxicity. The mechanism of FBM-induced toxicities is unknown; however, it has been proposed that 2-phenylpropenal, a reactive metabolite of FBM, is responsible. The pathway leading to this metabolite involves hydrolysis of FBM to 2-phenyl-1,3-propandiol monocarbamate (MCF), oxidation to 3-carbamoyl-2-phenylpropionaldehyde (CBMA), and spontaneous loss of carbon dioxide and ammonia. We made a polyclonal antibody against 2-phenylpropenal bound to protein and confirmed its specificity using ELISA. We attempted to develop an animal model of FBM-induced aplastic anemia and/or hepatotoxicity, and we also used the antibody to try to detect covalent binding of 2-phenylpropenal using immunoblotting. However, none of the animals developed evidence of bone marrow or liver toxicity, and we were unable to detect covalent binding, possibly because significantly less 2-phenylpropenal is formed in rodents than in humans. As this type of idiosyncratic drug reaction is believed to be immune-mediated, we also studied the potential of FBM and its metabolites to stimulate an immune response using the reporter antigen popliteal lymph node assay in female Balb/c mice. We found that neither FBM nor MCF induced an immune response in popliteal lymph nodes (PLNs). However, CBMA treatment appeared immunogenic, causing footpad inflammation, hardening, scab formation, and an increase in thickness. The PLN cell count in CBMA-treated mice increased 8-fold as compared to control, FBM-, or MCF-treated mice. Immunohistochemical analysis of the CBMA-exposed PLNs revealed germinal center formation, indicating B cell proliferation, later confirmed by flow cytometry. Most of the cells expressing the activation surface marker CD54 were B cells. We also found that CBMA treatment caused an increase in the production of IgM and IgG1 antibodies as well as IL-4 and IFN-gamma cytokines. Our findings indicate that 2-phenylpropenal is a very potent immunogen, supporting its possible involvement in the FBM-induced hepatotoxicity and aplastic anemia.

Differential requirement for the CD40-CD154 costimulatory pathway during Th cell priming by CD8 alpha+ and CD8 alpha- murine dendritic cell subsets

Dendritic cells (DCs) regulate the development of distinct Th populations and thereby provoke appropriate immune responses to various kinds of Ags. In the present work, we investigated the role CD40-CD154 interactions play during the process of Th cell priming by CD8 alpha(+) and CD8 alpha(-) murine DC subsets, which have been reported to differently regulate the Th response. Adoptive transfer of Ag-pulsed CD8 alpha(+) DCs induced a Th1 response and the production of IgG2a Abs, whereas transfer of CD8 alpha(-) DCs induced Th2 cells and IgE Abs in vivo. Induction of distinct Th populations by each DC subset was also confirmed in vitro. Although interruption of CD80/CD86-CD28 interactions inhibited Th cell priming by both DC subsets, disruption of CD40-CD154 interactions only inhibited the induction of the Th1 response by CD8 alpha(+) DCs in vivo. CD40-CD154 interactions were not required for the proliferation of Ag-specific naive Th cells stimulated by either DC subset, but were indispensable in the production of IL-12 from CD8 alpha(+) DCs and their induction of Th1 cells in vitro. Taken together, in our immunization model of Ag-pulsed DC transfer, CD40-CD154 interactions play an important role in the development of CD8 alpha(+) DC-driven Th1 responses but not CD8 alpha(-) DC-driven Th2 responses to protein Ags.

CD40 ligand in pathogenesis of autoimmune ovarian disease of day 3-thymectomized mice: implication for CD40 ligand antibody therapy

The blockade of CD40 ligand (CD40L) is effective in autoimmune disease prevention. Recently, a brief period of CD40L mAb treatment was reported to induce tolerance and enhancement of CD4(+)CD25(+) regulatory T cell activity. We therefore determined the efficacy of CD40L mAb treatment in autoimmunity that resulted from CD4(+)CD25(+) regulatory T cell deficiency. Autoimmune ovarian disease (AOD) and oocyte autoantibody response of day 3-thymectomized (d3tx) mice were inhibited by continuous CD40L mAb treatment from day 3, or from days 10-14, whereas CD40L mAb treatment confined to the neonatal week was ineffective. The enhanced expression of memory markers (CD44 and CD62L(low)) on CD4(+) T cells of the d3tx mice was unaffected by CD40L mAb treatment. In contrast, their increased T cell activation markers (CD69 and CD25) were eliminated by CD40L mAb treatment. Moreover, ex vivo activated T cells of d3tx mice expressed elevated intracellular IFN-gamma, and this was also blocked by CD40L mAb. The memory T cells, although nonpathogenic in CD40L mAb-positive environment, transferred severe AOD to CD40L mAb(-) neonatal recipients. Most importantly, CD40L mAb treatment inhibited AOD in recipients of T cells from d3tx donors with severe AOD and led to regression of AOD in d3tx mice documented at 4 wk. Therefore, 1) the continuous presence of CD40L mAb both prevents and causes regression of AOD in the d3tx mice; and 2) the multiple steps of the d3tx autoimmune disease, including T cell activation, cytokine production, T cell-mediated inflammation, and tissue injury, are CD40L dependent.

Chemical-specific properties co-determine the type of adverse immune response

Many drugs but also environmental pollutants may cause adverse reactions in susceptible individuals that are reminiscent of autoimmune syndromes. Apart from a number of predisposing often inherent, idiosyncratic determinants, chemical-specific properties might be involved as well. Notably, reactive chemicals or metabolites may provoke formation or release of immunosensitizing neo-antigens (a.o. hapten-carrier complexes or cryptic epitopes). In addition reactive chemicals but also certain inert chemicals may trigger macrophages and other inflammatory cells to release proinflammatory products that, via elicitation of costimulatory help, support hapten- or neo-antigen-specific T cell activation. In addition, chemicals may influence immunoregulatory processes and modulate for instance the balance between type 1 and type 2 responses. Here, we review data showing that chemically induced upregulation of second or costimulatory signals co-determines not only whether, but also what type of an adverse immune response (type 1 or type 2) is triggered.