Regulation of the immune response to peptide antigens: differential induction of immediate-type hypersensitivity and T cell proliferation due to changes in either peptide structure or major histocompatibility complex haplotype

VaxCelerate II: rapid development of a self-assembling vaccine for Lassa fever

Development of effective vaccines against emerging infectious diseases (EID) can take as much or more than a decade to progress from pathogen isolation/identification to clinical approval. As a result, conventional approaches fail to produce field-ready vaccines before the EID has spread extensively. Lassa is a prototypical emerging infectious disease endemic to West Africa for which no successful vaccine is available. We established the VaxCelerate Consortium to address the need for more rapid vaccine development by creating a platform capable of generating and pre-clinically testing a new vaccine against specific pathogen targets in less than 120 d A self-assembling vaccine is at the core of the approach. It consists of a fusion protein composed of the immunostimulatory Mycobacterium tuberculosis heat shock protein 70 (MtbHSP70) and the biotin binding protein, avidin. Mixing the resulting protein (MAV) with biotinylated pathogen-specific immunogenic peptides yields a self-assembled vaccine (SAV). To meet the time constraint imposed on this project, we used a distributed R&D model involving experts in the fields of protein engineering and production, bioinformatics, peptide synthesis/design and GMP/GLP manufacturing and testing standards. SAV immunogenicity was first tested using H1N1 influenza specific peptides and the entire VaxCelerate process was then tested in a mock live-fire exercise targeting Lassa fever virus. We demonstrated that the Lassa fever vaccine induced significantly increased class II peptide specific interferon-γ CD4(+) T cell responses in HLA-DR3 transgenic mice compared to peptide or MAV alone controls. We thereby demonstrated that our SAV in combination with a distributed development model may facilitate accelerated regulatory review by using an identical design for each vaccine and by applying safety and efficacy assessment tools that are more relevant to human vaccine responses than current animal models.

Anaphylaxis caused by repetitive doses of a GITR agonist monoclonal antibody in mice

Immunotherapy for cancer using antibodies to enhance T-cell function has been successful in recent clinical trials. Many molecules that improve activation and effector function of T cells have been investigated as potential new targets for immunomodulatory antibodies, including the tumor necrosis factor receptor superfamily members GITR and OX40. Antibodies engaging GITR or OX40 result in significant tumor protection in preclinical models. In this study, we observed that the GITR agonist antibody DTA-1 causes anaphylaxis in mice upon repeated intraperitoneal dosing. DTA-1-induced anaphylaxis requires GITR, CD4(+) T cells, B cells, and interleukin-4. Transfer of serum antibodies from DTA-1-treated mice, which contain high levels of DTA-1-specific immunoglobulin G1 (IgG1), can induce anaphylaxis in naive mice upon administration of an additional dose of DTA-1, suggesting that anaphylaxis results from anti-DTA-1 antibodies. Depletion of basophils and blockade of platelet-activating factor, the key components of the IgG1 pathway of anaphylaxis, rescues the mice from DTA-1-induced anaphylaxis. These results demonstrate a previously undescribed lethal side effect of repetitive doses of an agonist immunomodulatory antibody as well as insight into the mechanism of toxicity, which may offer a means of preventing adverse effects in future clinical trials using anti-GITR or other agonist antibodies as immunotherapies.

HLA-DRB1 alleles control allergic bronchopulmonary aspergillosis-like pulmonary responses in humanized transgenic mice

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a lung hypersensitivity disease mediated in part by CD4(+) T(H)2 cells. There is a significant association between ABPA and the HLA-DR2 genotypes DRB1(*)1501 and DRB1(*)1503, whereas resistance might be associated with HLA-DRB1(*)1502.

OBJECTIVE

We sought to elucidate the role of HLA-DR alleles in allergic inflammation in lungs.

METHODS

HLA-DR humanized transgenic mice expressing either the susceptible or resistant alleles were analyzed for the nature and extent of pulmonary inflammation after exposure to Aspergillus species antigens.

RESULTS

Exposed DRB1(*)1501 and DRB1(*)1503 transgenic mice displayed infiltrates made up prominently of eosinophils, which is consistent with the inflammation found in ABPA. The resistant DRB1(*)1502 mice, on the other hand, displayed minimal to moderate inflammation, consisting mainly of T-cell infiltrates. Significantly more mucin was produced in the DRB1(*)1503 and DRB1(*)1501 mice, and their ability to limit the number of Aspergillus species conidia within the lung parenchyma was impaired. Despite their differences, both the DRB1(*)1503 and DRB1(*)1502 strains mounted comparable T cell-proliferative responses to Aspergillus species antigens.

CONCLUSION

The HLA-DR2 alleles DRB1(*)1501 and DRB1(*)1503 play a major role in the development of allergic pulmonary inflammation. In contrast, the HLA-DR2 allele DRB1(*)1502 mediates a nonallergic T(H)1-like response to the organism, possibly explaining an ABPA resistance factor. These results are in support of our published human studies in patients with cystic fibrosis and asthma.

CLINICAL IMPLICATIONS

HLA-DR typing in patients with cystic fibrosis and asthma will aid in the identification of individuals at risk for ABPA.

How dietary antigens access the mucosal immune system

The intestinal epithelium is a selective barrier where incompletely-digested food antigens are transmitted to the immune system. Food antigens are often the starting point of intestinal diseases such as food allergy or coeliac disease. The intestinal epithelial cells (IEC) take up and process food antigens mainly by fluid-phase transcytosis involving two functional pathways, one minor direct pathway without degradation and another major lysosomal degradative pathway. Among the peptidic metabolites generated during transepithelial transport of luminal antigens, some have a molecular mass compatible with a binding to restriction (major histocompatibility complex; MHC) molecules; the latter can be up regulated on enterocytes, especially in inflammatory conditions. Indeed, interferon-γ not only increases the paracellular absorption of antigens, but also their transcytosis across epithelial cells. It has been reported that enterocytes may even directly present peptidic epitopes to underlying T-cells. As a new potential way of transmitting peptidic information to the local or systemic immune system, the secretion by IEC of antigen-presenting vesicles called exosomes and bearing MHC–peptide complexes has recently been proposed. Many other factors such as nutritional or environmental factors can also influence the properties of the epithelial barrier and the outcome of the immune response to lumen antigens.

Antagonism of HIV-specific CD4+ T cells by C-terminal truncation of a minimum epitope

Antagonism of T cell responses by variants of the cognate peptide is a potential mechanism of viral escape from immune responses and may play a role in the ability of HIV to evade immune control. We show here a rarely described mechanism of antagonism by a peptide shorter than the minimum length epitope for an HIV p24-specific CD4+ T cell clone. The shorter antagonist peptide-MHC complex bound the T cell receptor (TCR), albeit with lower affinity than the full-length agonist peptide. Prior work showing the crystal structure of the peptide-MHC complex revealed a unique glycine hinge near the C-terminus of the agonist peptide, allowing the generation of full-length antagonist peptide lacking the hinge. These results confirm the dependence of productive TCR engagement on residues spilling out from the C-terminus of the MHC binding groove and show that partial engagement of the TCR with a truncated, low-affinity ligand can result in T cell antagonism.

Specificity, degeneracy, and molecular mimicry in antigen recognition by HLA-Class II restricted T cell receptors: implications for clinical medicine

Abstract In humans, increased susceptibility to specific autoimmune diseases is closely associated with specific HLA-class II alleles. CD4(+) T cells that recognize short self-peptides in the context of HLA-class II molecules via their T cell receptor (TCR) are considered to mediate the central role of pathogenesis in autoimmunity. Although both self- and nonself-peptides are presented on HLA-class II molecules under physiological conditions, several mechanisms exist to avoid the T cell response to the self-peptide/HLA-class II complex. One of the mechanisms that account for the breakdown in immune tolerance is cross-recognition by TCR between a pathogen-derived antigen and a host antigen (molecular mimicry theory). Epidemiological studies have indicated that a number of autoimmune diseases are developed or exacerbated after infections. Therefore, elucidating the recognition nature of HLA-class II restricted TCR in detail is necessary in order to understand disease processes. A large body of evidence indicates that T cell recognition is highly degenerate, and many different peptides can activate an individual T cell. Degeneracy of TCR recognition also can appear in various physiological outcomes, ranging from full activation to strong antagonism. Here, we review the clinical implications of our findings on T cell recognition, as well as a new direction of future applications for analyses in molecular mimicry. We also describe the latest developments in methods of mapping TCR epitopes for CD4(+) T cells using a peptide epitope expression library generated in the class II-associated invariant chain peptide substituted invariant chain gene format.

Modulation of CD4 T cell function by soluble MHC II-peptide chimeras

Peptides antigens of 8 to 24 amino acid residues in length that are derived from processing of foreign proteins by antigen presenting cells (APC), and then presented to T cells in the context of major histocompatibility complex molecules (MHC) expressed by APC, are the only physiological ligands for T cell receptor (TCR). Co-ligation of TCR and CD4 co-receptor on T cells by MHC II-peptide complexes (signal 1) leads to various T cell functions depending on the nature of TCR and CD4 co-ligation, and whether costimulatory receptors (signal 2) such as CD28, CTLA-4, CD40L are involved in this interaction. Recently, the advance of genetic engineering led to the generation of a new class of antigen-specific ligands for TCR, i.e., soluble MHC class I-, and MHC class II-peptide chimeras. In principle, these chimeric molecules consist of an antigenic peptide which is covalently linked to the amino terminus of alpha-chain in the case of MHC I, or beta-chains in the case of MHC II molecules. Conceptually, such TCR/CD4 ligands shall provide the signal 1 to T cells. Since soluble MHC-peptide chimeras showed remarkable regulatory effects on peptide-specific T cells in vitro and in vivo, they may represent a new generation of immunospecific T cell modulators with potential therapeutic applicability in autoimmune and infectious diseases. This review is focused on the immunomodulatory effects of soluble, MHC class II-peptide chimeras, and discuss these effects in the context of the most accepted theories on T cell regulation.

An unexpected version of horror autotoxicus: anaphylactic shock to a self-peptide

EAE can refer either to experimental autoimmune encephalomyelitis or experimental allergic encephalomyelitis. Although EAE is classically a prototypic T helper 1 (TH1) cell-mediated autoimmune disease, it can also be induced by TH2 cells. Characteristically, the most severe manifestation of allergy, anaphylaxis, is associated with exposure to a foreign antigen that is often derived from medication, insect venom or food. We report here that, after self-tolerance to myelin is destroyed, anaphylaxis may be triggered by a self-antigen, in this case a myelin peptide. "Horror autotoxicus", which was initially described by Ehrlich, may not only include autoimmunity to self, it may also encompass immediate hypersensitivity to self, which leads to shock and rapid death.

Evaluation of the impact of food technology on the allergenicity of cow's milk proteins

The quantitative evaluation of the allergenicity of food proteins and the clinical tolerance towards antigens are problems the food industry and the clinicians have to face. The allergenicity of a protein depends on multiple factors, including the stability to digestion and the interaction with the intestinal environment. In addition to the possible reduction in allergenicity by technological treatments such as heat and enzymic hydrolysis, the complex interactions existing between the antigens, the intestinal epithelium and the underlying immune system, as well as the individual susceptibility to the sensitizing epitopes, have to be taken into account. Indeed, the intestinal cells are able to take up and process proteins, and possibly to present them directly to mucosal lymphocytes. On the other hand, pathophysiological conditions can modify the interactions between food antigens and the immune system. A large number of methods has been developed to assess the residual antigenicity of food proteins, based on the various immune responses leading to intestinal or extradigestive pathologies. Thus, the difficulty in measuring the residual allergenicity of hypoallergenic formulas is partly due to the physiology of the gastrointestinal tract, since an intricate network of interactions between enterocytes and immune cells governs the development of the immune response to food antigens.

Peptide-based molecular analyses of HLA class II-associated susceptibility to autoimmune diseases

Recent advances in knowledge of crystal structures of MHC class II molecules has advanced understanding of the molecular basis for interactions between peptides and HLA class II molecules. Polymorphism of HLA class II molecules influences structures of peptides bound to HLA class II molecules. To better understand mechanisms related to particular HLA class II alleles and autoimmune diseases, it is important to identify self-peptides presented by disease-susceptible HLA class II molecules and triggering disease-causative autoreactive T cells. Autoimmune diseases occur in Caucasians, Blacks and Asians, albeit with a different incidence. In some autoimmune diseases, disease-susceptible HLA class II alleles are closely related but different, and clinical manifestations of diseases differ among ethnic groups. These phenomena strongly suggest that difference in autoimmune self-peptide(s) in the context of disease-susceptible HLA class II molecules may explain the different clinical manifestations of diseases. Therefore, a comparison among disease-susceptible HLA class II alleles, autoimmune self-peptides and clinical manifestations of autoimmune diseases in different ethnic groups would be instructive. We directed efforts to determining: (1) HLA-class II alleles specific to Asian populations and which are associated with susceptibility to autoimmune diseases, (2) binding-peptide motifs for these HLA class II molecules, and (3) self-peptides presented by susceptible HLA class II molecules to stimulate autoreactive T cells related to the development of autoimmune diseases in Asians. In this review, our related recent investigations are described and the uniqueness of HLA class II-associated autoimmune diseases in Asians is given emphasis.

Molecular analyses of HLA class II-associated susceptibility to subtypes of autoimmune diseases unique to Asians

It is well known that individuals positive for particular HLA-class II alleles show high risks for the development of Takayasu arteritis and other diseases caused by immunological disorders such as autoimmune diseases and allergies. HLA class II molecules present antigenic peptides to CD4+ T cells. Their extensive polymorphism affects the structures of peptides bound to HLA class II molecules to create individual differences in immune responses to antigenic peptides. To better understand the mechanisms for association between HLA class II alleles and susceptibility to autoimmune diseases, it is important to identify self-peptides presented by disease-susceptible HLA class II molecules and triggering disease-causative T cells. Many autoimmune diseases are observed in all ethnic groups, whereas the incidences of diseases, clinical manifestations and disease-susceptible HLA class II alleles are different among various ethnic groups for some autoimmune diseases. These phenomena suggest that differences in autoimmune self-peptide(s) in the context of disease-susceptible HLA class II molecules may cause these differences. Therefore, comparisons among disease-susceptible HLA class II alleles, autoimmune self-peptides and clinical manifestations of autoimmune diseases in different ethnic groups would be helpful in determining the pathogenesis of the diseases. In this paper, we describe our recent findings on: (1) the uniqueness of both clinical manifestations and HLA-linked genetic background of Asian-type (optico-spinal form) multiple sclerosis; (2) the structural characteristics of peptides bound to HLA-DQ molecules susceptible to insulin-dependent diabetes mellitus; (3) the identification of a disease-related autoantigenic peptide presented by disease-susceptible HLA-DQ molecules in Asians-specific infant onset myasthenia gravis; and (4) a manipulation of human T cell response by altered peptide ligands, as a possible candidate for new and antigen-specific immuno-suppressive therapy against autoimmune diseases.

Characteristics of Prevotella intermedia-specific CD4+ T cell clones from peripheral blood of a chronic adult periodontitis patient

Periodontitis is a chronic destructive inflammatory disease associated with periodontopathic bacteria. In addition, autoantigens such as collagen and heat shock proteins (hsp) have been suggested to play a role. Established periodontal lesions are characterized by dense infiltrations of immune cells such as cytokine-producing CD4+ and CD8+ T cells. CD4+ T cells specific for Prevotella intermedia can be isolated from lesional gingiva, suggesting an active role for CD4+ T cells in the response to this bacterium. We therefore investigated the characteristics of a panel of 13 P. intermedia-specific CD4+ T cells generated from the peripheral blood of a patient with chronic adult periodontitis. All 13 P. intermedia-specific CD4+ T cells recognized the antigens in the context of HLA-DR. The T cell clones were mainly classified as Th0, producing comparable amounts of interferon-gamma (IFN-gamma) and IL-4, and Th2, producing high amounts of IL-4 and almost no IFN-gamma. None of the P. intermedia-specific T cell clones recognized antigens of the periodontopathic bacteria Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis and of the autoantigens collagen and hsp. The reactivity profile of the T cell clones to size-fractionated cell envelope antigens of P. intermedia indicated that P. intermedia-specific CD4+ T cell clones recognize probably five different antigen specificities in the context of the MHC class II molecules, DR7 or DR15. These results suggest that a broad panel of cell-associated protein antigens play a role in the induction of P. intermedia-specific CD4+ T cell response.

T-cell receptor repertoires utilized in response to linear peptides representing an immunodominant MHC class II restricted T-cell epitope are far more diverse than that utilized in response to the same epitope in the nominal antigen

Previous analyses of the T-cell receptor (TCR) repertoire utilized in response to the 1-102 fragment of the lambda cI repressor protein and specific for the immunodominant amino acid 12-26 region in the context of I-Ek, have shown this repertoire to be extremely restricted. In contrast, here we show that the TCR repertoires utilized in two strains of I-Ek expressing mice in response to two linear peptides representing this immunodominant region are diverse. Despite their extensive diversity, these repertoires are somewhat overlapping. In addition, structural similarities were observed between the full lambda cI fragment (1-102) and peptide elicited TCR repertoires, including frequent use of the Valpha2 family of gene segments, particularly among peptide (12-26) elicited TCRs cross-reactive with 1-102/I-Ek. Nevertheless, these data indicate that it may be difficult to mimic the immune response to an immunodominant epitope of a protein antigen via immunization with linear peptides containing the amino acid sequence of that epitope. Possible explanations for differences in the levels of TCR diversity among T cells responding to an epitope present in a nominal antigen as compared to T cells responding to linear peptide antigens containing this same epitope are discussed.

Protein transport and processing by human HT29-19A intestinal cells: effect of interferon gamma

BACKGROUND

The nature of the breakdown products produced in enterocytes during epithelial transport of intact proteins may be critical in determining the functional consequences of protein absorption.

AIM

(a) To measure the transepithelial transport of horseradish peroxidase (HRP) and to identify the nature of HRP breakdown products released on the basal side of enterocytes and (b) to assess the role of interferon gamma (IFN gamma) on HRP transport and processing.

METHODS

HT29-19A intestinal cells were used to assess transepithelial transport of HRP in Ussing chambers, and the nature of breakdown products in the basal compartment was analysed by high performance liquid chromatography (HPLC).

RESULTS

(1) In control conditions, [3H]HRP equivalent fluxes (3135 (219) ng/h per cm2; mean (SEM) comprised 50% amino acids, 40% peptides, and 10% intact HRP. Steric exclusion HPLC of the breakdown products indicated a wide range of molecular masses including a major peptide of about 1150 Da. Lysosomal aspartyl and thiol proteases were expressed but no HLA-DR surface expression was noted, (2) At 48 to 72 hours after IFN gamma stimulation, [3H]HRP equivalent fluxes increased significantly (7392 (1433) ng/h per cm2) without modification of the relative proportions of amino acids, peptides, and intact HRP, and without modification of the distribution of breakdown products in HPLC. Lysosomal protease activities were not modified by IFN gamma but HLA-DR expression was increased.

CONCLUSION

Intestinal cells are able to process HRP into peptides potentially capable of stimulating the immune system. IFN gamma stimulates the transport and processing of HRP thus increasing the antigenic load in the intestinal mucosa.

How the MHC selects Th1/Th2 immunity

While the effects of cytokines on T helper 1 (Th1)/Th2 differentiation are well documented, it is less clear why a dichotomy of effector cytokine production would initiate from antigen-specific lymphocytes. Nevertheless, in defined experimental systems, the interaction between T-cell receptor (TCR), peptide and major histocompatibility complex (MHC) can determine Th1/Th2 dominance. Here, Joseph Murray discusses how TCR affinity and ligand density might interface with innate forces in the selection of CD4+ T-cell functions.

Immuno-suppressive peptides for a human T cell clone autoreactive to a unique acetylcholine receptor alpha subunit peptide presented by the disease-susceptible HLA-DQ6 in infant-onset myasthenia gravis

Infant-onset myasthenia gravis, an autoimmune disease specific to Asians predominantly affects neuromuscular junctions in ocular muscles. An AChR alpha peptide (p71-91) specific autoreactive CD4+ alpha beta T cell clone was established by stimulating PBMC from a patient heterozygous for two disease-susceptible HLA-DR9-DQ9 and DR13-DQ6 haplotypes with a mixture of overlapping peptides covering AChR alpha. The T cell clone recognized the AChR alpha peptide in the context of the HLA-DQ6 molecule and produced a large amount of IFN-gamma and a trace amount of IL-4. A part (p75-83) of the core epitope of the autoantigenic peptide (p75-87) is encoded for by an exon P3A of the AChR alpha gene which can be alternatively spliced. The T cell clone responded to the recombinant AChR alpha protein with a P3A exon product, but not without a P3A exon product. We investigated responses of the T cell clone to 114 analogue peptides carrying single residue substitutions of the core AChR alpha peptide. The majority of analogues substituted at residues Phe-77, Leu-80 and Asn-82 stimulated proliferation of the T cell clone. Conversely, the majority of analogue peptides substituted at either Gln-81 or Glu-83 did not stimulate proliferative responses, and all exhibited strong or intermediate inhibitory effects on proliferative responses of the T cell clone to the wild type peptide, possibly by TCR antagonism. Thus, an HLA class II allele specific to Asians may directly control susceptibility to the Asian-specific type of myasthenia gravis. Analogues of the auto-antigenic AChR alpha peptide may prove effective for new immunosuppressive therapy.

A single residue polymorphism at DR beta 37 affects recognition of peptides by T cells

Single amino acid polymorphism at residue 37 of the HLA-DR beta chain (DR beta 37) between DRB1*0406 and 0403 markedly influences susceptibility to the insulin autoimmune syndrome. We investigated the effects of DR beta 37 polymorphism regarding recognition of nonself peptides by a T-cell clone, YN5-32, specific to a streptococcal peptide (M12p54-68) presented by the DRB1*0406 molecule. YN5-32 responded better to M12p54-68 presented by allogeneic DRB1*0403 with a single Tyr-substitution at DR beta 37-Ser of the DRB1*0406 molecule. One hundred and fifty-four peptides carrying single residue substitutions at each of the core residues 57-65 of M12p54-68, were tested for full agonistic and TCR antagonistic activities. Forty-six peptides showed full agonism, 34 analogues exhibited TCR antagonism, and 45 analogues exhibited neither full agonism nor TCR antagonism, irrespective of the presenting molecules (DRB1*0406 or 0403). On the other hand, 29 analogue peptides substituted at each of residues 57-63 of M12p54-68 were recognized differently by YN5-32, depending on the presenting molecules. These observations indicate that 1) single amino acid polymorphism (Ser-Tyr) at the DR beta 37 residue induced a conformational change distinguished by TCR in some but not all peptides; and 2) these conformational changes were observed even in analogue peptides carrying single residue substitutions at residues far from a putative DR beta 37 contact site. These findings provide further evidence for altered human T-cell responses induced by TCR ligands with minor modifications.

Genetically transferred central and peripheral immune tolerance via retroviral-mediated expression of immunogenic epitopes in hematopoietic progenitors or peripheral B lymphocytes

BACKGROUND

Based on the hypothesis that IgGs are potent tolerogens and that immature lymphohematopoietic antigen-presenting cells (APC), and even mature peripheral B cells, may be effective APC for tolerance induction, we designed an immunoglobulin fusion protein retroviral expression vector to test the role of B cells in a novel gene therapy strategy for the transfer of immune tolerance.

METHODS

An immunodominant epitope (residues 12-26 of the lambda repressor cI protein) was fused in frame to an IgG heavy chain in a retroviral vector, which was used to infect either bone marrow cells or activated peripheral B lymphocytes. These cells were transferred into syngeneic recipients, who were subsequently challenged with the 12-26 peptide in adjuvant.

RESULTS

Bone marrow (BM) chimeras generated with retrovirally transduced bone marrow were shown to be profoundly unresponsive to the 12-26 peptide at both the humoral and cellular levels, but were competent to respond to an unrelated protein (lysozyme or PPD). Importantly, we also show that immunocompetent adult recipients infused with transduced mature, activated B lymphocytes, are rendered unresponsive by this treatment. Surprisingly, lymphoid-deficient BM progenitors from syngeneic SCID donors could also be transduced to produce tolerogenic APC.

CONCLUSIONS

Our data suggest that activated B cells are sufficient to be effective tolerogenic APC in immunocompetent adult mice, but that nonlymphoid cells may also induce tolerance in reconstituted hosts. This approach for gene-transferred tolerogenesis has the potential to be maintained indefinitely, and it requires only knowledge of cDNA sequences of target antigens.

The intensity of T cell receptor engagement determines the cytokine pattern of human allergen-specific T helper cells

Enhanced production of T helper (Th)2 cytokines by allergen-specific Th cells plays a major role in the induction and maintenance of IgE-mediated allergic disorders. The mechanism that triggers this type of response in atopic individuals is not fully understood. Allergen-specific human Th cell clones produce interleukin (IL)-4 and low or undetectable levels of interferon (IFN)-gamma after stimulation with low concentrations of antigen. However, these Th cell clones are capable of generating significant amounts of IFN-gamma after optimal activation through their T cell receptor (TcR). Allergen-specific Th cell clones isolated from allergic individuals required higher doses of antigen to reach the plateau of proliferation and to generate Th0 cytokine responses than their counterparts isolated from nonallergic subjects. On the other hand, if allergen was replaced by anti-CD3 monoclonal antibody (mAb), both allergic and nonallergic Th cell clones attained the highest level of proliferation and significant IFN-gamma production in response to equivalent concentrations of anti-CD3 mAb. These results indicate that the strength of T cell ligation, which can be modulated by the availability of the TcR ligand, controls the balance of Thl/Th2 cytokines produced by memory Th cells in vitro. In the particular case of bee venom phospholipase A2, it is shown that the expression of allergen-specific surface Ig on antigen-presenting B cells has little influence on antigen uptake and therefore in determining the levels of T cell activation and cytokine production. Alternatively, the affinity of particular major histocompatibility complex class II molecules on antigen-presenting cells for allergen-derived peptides might determine the amount of specific ligand presented to the Th cells and play a decisive role skewing the Th cell cytokine production towards Th1 or Th2 phenotypes. These findings, which are consistent with the changes in cytokine patterns observed following clinical hyposensitization, suggest that polarized human Th2 cell subsets still retain the capacity to modulate their cytokine pattern.

Analysis of interleukin-4 and interleukin-10 and their association with the lymphocytic infiltrate in the small intestine of patients with coeliac disease

BACKGROUND

Concentrations of pro-inflammatory cytokines are raised in the small intestine of patients with coeliac disease after ingestion of gluten but there are equivalent data on interleukin-4 (IL-4) and interleukin-10 (IL-10) producing cells. These cytokines are known to exert important regulatory effects on pro-inflammatory cytokine production from lymphocytes and macrophages.

AIMS

To investigate whether there is a primary deficiency of IL-4 and IL-10 producing cells and their site of production in the small intestine of patients with coeliac disease in relation to the changes in inflammatory cell infiltrate.

PATIENTS

Jejunal biopsy specimens from patients with coeliac disease (11 untreated, 10 treated) and nine disease controls were studied.

METHODS

Immunohistochemical staining of sections for IL-4 and IL-10 cytokines and the cell phenotypic markers CD3 (T lymphocytes) and CD45 (total inflammatory cell infiltrate) was carried out using monoclonal antibodies. Expression of IL-4 and IL-10 messenger RNA was detected by in situ hybridisation with oligonucleotide probe cocktails for each cytokine.

RESULTS

IL-4 and IL-10 mRNA and protein were detected in the lamina propria of treated and untreated coeliac patients and disease controls but not in the epithelium. A significant increase in the number of CD45 (p < 0.005) and CD3 (p < 0.05) positive cells was found in the lamina propria of patients with untreated coeliac disease compared with treated coeliac patients and disease controls but there were no differences in IL-4 or IL-10 between these groups with either method.

CONCLUSIONS

There is no primary deficiency of IL-4 and IL-10 producing cells in the small intestine of patients with coeliac disease. Detectable concentrations of IL-4 and IL-10 were found in control patients which suggests that these cytokines are involved in normal mucosal immunoregulation. The increased number of T lymphocytes but not IL-4 or IL-10 producing cells in the lamina propria of patients with untreated than in those with treated disease suggests not only that the lamina propria is the major mucosal compartment for cytokine production but that newly recruited mucosal T lymphocytes are directed to a predominant Th1 and not a Th2 cytokine response in coeliac patients on a diet containing gluten.

Induction of class II major histocompatibility complex blockade as well as T cell tolerance by peptides administered in soluble form

Peptides binding to a particular class II major histocompatibility complex (MHC) molecule can inhibit the activation of T cells by other peptides binding to the same molecule, a phenomenon termed class II MHC blockade. All class II-binding peptides exert MHC blockade in vivo in depot form with adjuvant, and some also retain their blocking properties in soluble form. We demonstrate here that soluble peptides, when used at doses causing short-term MHC blockade, can also induce long-term antigen-specific T cell tolerance to themselves. The tolerogenicity of soluble peptides correlates with their antigenicity in adjuvant, but it is not necessarily related to their capacity to act as class II blockers in vivo. The tolerant state is manifested in a decreased production of both T helper cell 1 (Th1)-type and Th2-type lymphokines, and it cannot be reversed by interleukin-2. Once T cells are primed with a peptide in complete Freund's adjuvant, they are resistant to tolerization with the same peptide applied in soluble form. Tolerance induction is partially impaired in B cell-deficient mu MT-/- mice, suggesting a role for B cell antigen presentation in this process. The results suggest that the potential immunogenicity of class II MHC blockers could be circumvented by choosing a tolerogenic mode of application.

Development of Th 1- or Th 2-dominated immune responses: what about the polarizing signals?

Type 1 helper T cells and type 2 helper T cells represent two extremely polarized forms of the effector specific immune response, based on a distinctive profile of cytokine production. Type 1- and type 2 helper T cell-dominated immune responses play a different role in both protection and immunopathology. The differentiation of effector phenotypes depends on a complex matrix of interconnecting factors resulting from the evolutionary interplay between vertebrates and microorganisms. These include the physical form of the antigen, as well as the density and affinity of the peptide ligand, the cytokines produced by "natural" immunity cells at the time of antigen presentation, costimulatory signals provided by antigen-presenting cells, and hormones released into the microenvironment. The elucidation of genetic and environmental factors that regulate type 1 or type 2 helper T cell development in response to different antigenic stimulation is the basis for new immunotherapeutic strategies in allergic and autoimmune disorders, as well as for the improvement of vaccines.

Epitope-specific tolerance induction with an engineered immunoglobulin

Isologous and heterologous immunoglobulins have been shown to be extremely effective as tolerogenic carriers for nearly 30 years. The efficacy of these proteins is due in part to their long half-life in vivo, as well as their ability to crosslink surface IgM with Fc receptors. The concept of using IgG as a carrier molecule to induce unresponsiveness in the adult immune system has been exploited for simple haptens, such as nucleosides, as well as for peptides. To further evaluate the in vivo potential of these molecules for inducing tolerance to a defined epitope, we have engineered a fusion protein of mouse IgG1 with the immunodominant epitope 12-26 from bacteriophage lambda cI repressor protein. This 15-mer, which contains both a B-cell and T-cell epitope, has been fused in-frame to the N terminus of a mouse heavy chain IgG1 construct, thus creating a "genetic hapten-carrier" system. We describe a novel in vitro and in vivo experimental system for studying the feasibility of engineered tolerogens, consisting of a recombinant flagellin challenge antigen and a murine IgG1 tolerogen, both expressing the lambda repressor epitope 12-26. Herein, we show that peptide-grafted IgG molecules injected i.v., or expressed by transfected, autologous B cells, can efficiently modulate the cellular and humoral immune responses to immunodominant epitopes. This model displays the feasibility of "tailor-designing" immune responses to whole antigens by selecting epitopes for either tolerance or immunity.

A combinatorial peptide library around variation of the human immunodeficiency virus (HIV-1) V3 domain leads to distinct T helper cell responses

The hypervariable domain of the HIV gp120, the V3 loop domain, represents a target for neutralizing antibodies and for HIV vaccine strategies. In this study, we have investigated in murine species the potential cross-reactivity of immune responses elicited by immunization either with individual V3 peptides, derived from distinct HIV sequences (BRU, RF, SF2, MN and ELI sequences), or with a V3 combinatorial peptide library. We observed that individual V3 peptides are immunogenic but elicit a specific B- and T-cell immune response that is mainly restricted to the sequence of the immunizing peptide. In particular, T-cell responses that depend on T-cell receptor recognition of peptides bound to the molecules encoded by the major histocompatibility complex were significantly influenced by small differences in the peptide amino acid sequence. The combinatorial V3 peptide library, previously described as B- and T-cell immunogens, induced a more broadly reactive immune response, specially when T-cell cytokine secretion was used as a readout for restimulation of T-cells with individual V3 peptides. These data suggest that amino acid variations in the sequence of an antigenic peptide could lead to the induction of different transducing signals in the primed T-cell population and to the activation of T-cells with distinct cytokine secretion properties. These observations may have implications in the understanding of antigenic variability and in the design of vaccine strategies.

Allergen dose dependent cytokine production regulates specific IgE and IgG antibody production

The elicitation of a specific immune response against allergens depends on the recognition of antigenic determinants (epitopes) by specific T and B lymphocytes. In order to determine the relevant epitopes for human T and B cells and their features in the regulation and production of specific IgE and/or IgG antibodies, we have investigated the immune response to bee venom phospholipase A2 (PLA) in allergic and non-allergic subjects. This enzyme represents the major allergen in bee sting allergy. It consists of 134 amino acid residues with a carbohydrate side chain at position 13 and is available as recombinant protein. We have developed PLA-specific T-cell clones from bee sting allergic and non-allergic human subjects. Using a panel of dodecapeptides overlapping in 10 residues and a large set of 18-25 mer overlapping peptides, we detected three epitopes that were recognized by peripheral blood T-cells and T-cell clones. A fourth determinant involved the carbohydrate moiety on Asn13 of PLA. Whereas the CHO-depending epitope seems to be mostly active in allergics, the other three epitopes are equally recognized by peripheral blood mononuclear cells (PBMC) of both allergic and non-allergic individuals. In T-cell clones, the ratio of IL-4/IFN gamma cytokines and the quality of the activating signal depend on the strength of the binding of the MHC-II/Ag/TcR complex between APC and T-cells. The number of antigen-specific APC-T-cell contact sites can be varied in vitro by changing the dose of antigen added to the cell culture. While isotype switch for both IgE and IgG4 requires IL-4, this cytokine suppresses antigen-specific IgG4 production by already switched B-cells. Therefore, IL-4 and IFN gamma display counter-regulatory effects on the production of IgE being responsible for atopic states and IgG4 antibodies which are signs of a normal immune response to allergen and act as protective antibodies. The combination of this counter-regulation of IgE and IgG4 antibodies with the fundamental law of mass action for chemical equilibrium reactions revealed that the antigen concentration governs to a great part the ratio of IL-4/IFN gamma secretion and therefore the formation of IgE and IgG and allergy or protection, together with the equilibrium constant K, which represents immunological individuality and a measure of Ag presentation.

Single amino acid substitutions on a Japanese cedar pollen allergen (Cry j 1)-derived peptide induced alterations in human T cell responses and T cell receptor antagonism

We generated T cell clones specific to a Japanese cedar pollen allergen (Cry j 1) and investigated effects of altered T cell receptor (TCR) ligand on changes of T cell responses. One of these Cry j 1-specific T cell clones established from patients with Japanese cedar pollinosis, ST1.9, recognized an antigenic peptide Cry j 1 p335-346 in the context of HLA-DRA+DRB3*0301 molecules and secreted interleukin-4 dominantly, with a smaller amount of interferon-gamma. ST1.9 represented one of the major T cell clones specific to Cry j 1 in the donor, because a short-term cultured polyclonal T cell line specific to Cry j 1 exhibited the same character as the ST1.9. We synthesized various analog peptides derived from Cry j 1 p335-346 with single amino acid substitutions and determined key residues for interactions between TCR of ST1.9 and HLA-DR molecules. We also analyzed changes in the responses of ST1.9 to Cry j 1 p335-346-derived analog peptides. Of interest was that the substitution of 339threonine to valine resulted in a significant increase in interferon-gamma production, with no remarkable changes either in proliferative response or interleukin-4 production. Analog peptides carrying the substitutions of 339threonine to glycine or glutamine revealed TCR antagonism, without changes in their binding affinities to the DR molecule. Therefore single amino acid substitutions on an allergen peptide carrying the T cell epitope may suppress helper-T-dependent class switch pressure to IgE in B cells either by inducing increased interferon-gamma production or by inhibiting proliferative responses in helper-T cells.

Major histocompatibility complex binding affinity of an antigenic determinant is crucial for the differential secretion of interleukin 4/5 or interferon gamma by T cells

Differential activation of CD4+ T-cell precursors in vivo leads to the development of effectors with unique patterns of lymphokine secretion. To investigate whether the differential pattern of lymphokine secretion is influenced by factors associated with either the display and/or recognition of the ligand, we have used a set of ligands with various class II binding affinities but unchanged T-cell specificity. The ligand that exhibited approximately 10,000-fold higher binding to I-Au considerably increased the frequency of interferon gamma-producing but not interleukin (IL) 4- or IL-5-secreting cells in vivo. Using an established ligand-specific, CD4+ T-cell clone secreting only IL-4, we also demonstrated that stimulation with the highest affinity ligand resulted in interferon gamma production in vitro. In contrast, ligands that demonstrated relatively lower class II binding induced only IL-4 secretion. These data suggest that the major histocompatibility complex binding affinity of antigenic determinants, leading to differential interactions at the T cell-antigen-presenting cell interface, can be crucial for the differential development of cytokine patterns in T cells.

Cysteine protease of the nematode Nippostrongylus brasiliensis preferentially evokes an IgE/IgG1 antibody response in rats

Some cysteine proteases such as papain and those of mites and schistosomes have potent allergenic properties. To clarify the allergenicity of nematode cysteine proteases, the enzyme was purified from the intestinal nematode Nippostrongylus brasiliensis using cation exchange chromatography and gel filtration chromatography. The purified protease, of 16 kD and pI 8.5, showed maximum enzyme activity at pH 5.5 and substrate preference for Z-Phe-Arg-MCA. The specific inhibitors of cysteine protease leupeptin, iodoacetic acid, and E-64, completely suppressed the activity, indicating that the purified enzyme belongs to the cysteine protease family. Cysteine protease activity was found not only in somatic extract, but also in the excretory-secretory (ES) product of the nematode. When anti-cysteine protease immunoglobulin isotypes were examined in sera from rats infected with N. brasiliensis, a high level of IgG1 and a lower level of IgE antibody were detected. Depletion of IgG antibodies from the sera using protein G affinity columns resulted in a marked increase in reactivity of anti-cysteine protease IgE with the antigen, possibly due to the removal of competing IgG antibodies. In contrast to IgE and IgG1, production of anti-cysteine protease IgG2a was negligible. These results indicate that the nematode cysteine protease preferentially evokes an IgE/IgG1 antibody response.

Clonal analysis of CD4 mediated accessory function on the effector activity of human CD4+ T cell subsets

BACKGROUND

It has been reported for the peripheral T cell repertoire that CD4 molecules may enhance adhesion between T cells and antigen presenting cells and, through their physical association with T cell antigen receptors, contribute to signal transduction.

OBJECTIVE

The aims of this study were to determine if the modulation of CD4 molecules had differential effects on T cell recognition, antigen induced cytokine (IL-4 and IFN gamma), release and the induction of specific anergy for human TH-0, Th-1 and TH-2 cells.

METHODS

A panel of anti-CD4 antibodies was examined for its ability to modulate T cell proliferation, cytokine production and tolerance induction in house dust mite (TH-0 and TH-2) and influenza haemagglutinin (TH-1) specific human CD4+ T cell clones all restricted by DRB1*1101 and isolated from dust mite allergic individuals.

RESULTS

We observed that anti-CD4 antibodies may inhibit or enhance antigen mediated T cell proliferation, which may reflect the differential requirements of T cells for selective functions of CD4. Furthermore, IFN gamma and IL-4 production was differentially modulated depending on the specificity of the anti-CD4 antibody and the clone of T cells. However, pretreatment of T cells with anti-CD4 antibody alone neither induced nor enhanced the susceptibility of T cells to peptide mediated anergy.

CONCLUSION

Antigen recognition by different subsets of human CD4+ T cells has differential requirements on CD4, whereas the induction of specific anergy appeared to be independent of the functions of CD4 molecules. Antigen induced IFN gamma production was more susceptible than IL-4 to the inhibitory effects of anti-CD4 antibodies. Furthermore, it appeared that certain anti-CD4 antibodies can dissociate antigen induced IFN gamma and IL-4 production, and may downregulate IFN gamma synthesis without inhibiting antigen dependent proliferation.

The effects of changes at peptide residues contacting MHC class II T-cell receptor on antigen recognition and human Th0 cell effector function

Cytokines can influence the selection of functional subsets (Th1 or Th2) of CD4+ T cells. However, quantitative changes in affinity of peptide/major histocompatibility complex (MHC) class II/T-cell receptor (TCR) interactions may alter antigen density and modulate T-cell effector function. The possibility exists to use peptide analogues to induce a partial signal to dissociate production of interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) by T-helper type-0 (Th0) cells and, consequently, to regulate T-cell function. Based on binding assays and resolution of the crystalline structure of an influenza virus haemagglutinin peptide (HA 306-318) bound to the human MHC class II molecule DRB1*0101, we synthesized HA peptide analogues with amino acid substitutions predicted to modify either MHC class II/peptide density or TCR/peptide interactions. When we examined their antigenicity using cloned human Th0 cells, the analogues, in general, elicited a gradation in potency reflected by a reduction in both proliferation and cytokine production (IL-2, IL-4 and IFN-gamma). Although the analogue HA-R309 diminished IL-2 production, none of the analogues tested could selectively induce only IL-4 or IFN-gamma. Since, in general, the effector functions of the Th0 cells examined here were resistant to selective manipulation by the peptide analogues, this suggests that for some clones of chronically activated T cells modulation of selected functions may be difficult to achieve.

The effect of a single amino acid substitution within the V3 loop of HIV-1 gp120 on HLA-DR1-restricted CD4 T-cell recognition

Viral variation has been proposed to play a role in the pathogenesis of human immunodeficiency virus type-1 (HIV-1) infection, and is an important consideration in vaccine design. During the course of an infection, isolates with sequence changes in CD8 T-cell and B-cell epitopes arise. To determine whether sequence variation within the V3 loop of HIV-1 gp120 affects HLA-DR beta 1*0101-restricted CD4 T-cell recognition, we have generated CD4 T-cell clones (TLC) specific to gp120 V3 loop peptides. Four HLA-DR beta 1*0101-restricted groups of TLC were defined by distinct patterns of responses to a panel of peptides, consistent with a highly diverse T-cell repertoire recognizing the 30 amino acid stretch (296-326) of the gp120 V3 loop. Nevertheless, a single residue change at position 311 was found to abolish the recognition of two of the four groups of TLC. This was not due to an effect of the residue at 311 on binding to major histocompatibility complex (MHC), because: (1) irrespective of the residue at 311, peptides competed well with the influenza haemagglutinin peptide 307-319 for binding to cell-bound DR1; and (2) R311-specific TLC were also HLA DR beta 1*0101 restricted. Instead, the substitution of arginine for serine at position 311 blocked the interaction of the peptide with the T-cell receptor. Thus, despite the diversity of the T-cell response to the V3 loop of HIV-1, a single amino acid change can have a considerable influence on the responding T-cell population. As residue 311 is one of the most variable of the V3 loop residues, these results suggest that CD4 recognition can also exert pressure on viral variation consistent with a role for these cells in antiviral immunity.

Preferential recognition of hepatitis B nucleocapsid antigens by Th1 or Th2 cells is epitope and major histocompatibility complex dependent

Regulatory T-helper (Th) cells have been categorized into two functional subsets, Th1 and Th2 cells, which produce distinct lymphokines. In general, Th1 cells mediate cellular immune responses and Th2 cells mediate humoral immunity. Recent serological studies suggest that the Th1-Th2 balance may be relevant in acute and chronic hepatitis B virus (HBV) infections. The purpose of this study was to determine the potential of the nucleocapsid antigens (Ags) (hepatitis B core and e Ags [HBc/eAg]) of HBV to preferentially elicit either a Th1 or a Th2 dominant response. For this purpose, H-2 congenic B10.S and B10 mice were immunized with HBc/eAg, and Ag-specific T-cell proliferative responses, T-cell helper function, and T-cell cytokine production were analyzed. The results indicated that B10.S mice preferentially develop a Th1-like response whereas B10 mice preferentially develop a Th2-like response after immunization with HBc/eAg. Furthermore, the preferential Th1 and Th2 response patterns were reproduced when 12-residue peptides representing the dominant HBc/eAg-specific T-cell sites for B10.S (peptide 120-131) and B10 (peptide 129-140) mice were used as immunogens. Therefore, the combination of the T-cell site recognized and the major histocompatibility complex restricting element can in large part determine the Th phenotype of the HBc/eAg-specific T-cell response. Other factors that influenced Th phenotype were the presence of exogenous cytokines, Ag structure, and tissue distribution.

Synthetic peptides representing T-cell epitopes act as carriers in pneumococcal polysaccharide conjugate vaccines

Improvement of antibody responses to polysaccharides through their linkage to proteins is thought to be mediated by protein-specific T helper (Th) cells. To investigate whether the carrier protein of a conjugate could be substituted by a Th epitope, Streptococcus pneumoniae type 17F polysaccharide (PS) was bromoacetylated and coupled to different peptides via their carboxy-terminal cysteines. Two peptides, one from the mycobacterial 65-kDa heat shock protein (hsp65) and the other from influenza virus hemagglutinin, are well-known Th epitopes. Two other peptides were selected from the pneumolysin sequence by Th epitope prediction methods; one of them was synthesized with cysteine either at the carboxy or the amino terminus. Three conjugates consistently elicited in mice anti-PS immunoglobulin M (IgM) and IgG responses that were not observed upon immunization with derivatized PS without peptide. The same conjugates induced no anti-PS antibody responses in athymic (nu/nu) mice, whereas clear responses were elicited in euthymic (nu/+) controls, demonstrating the thymus-dependent character of these conjugates. Only the three conjugates inducing anti-PS responses were capable of eliciting antipeptide antibodies. One of the immunogenic conjugates was studied in more detail. It induced significant protection and an anti-PS IgG response comprising all subclasses. On the basis of these results and proliferation studies with peptide and conjugate-primed cells, it is concluded that linkage of Th epitopes to PS in the right orientation enhances its immunogenicity in a thymus-dependent manner. Future possibilities for using peptides as carriers for inducing antibody responses to poorly immunogenic saccharide antigens are discussed.

Involvement of histamine or tumor necrosis factor in early-type hypersensitivity

A novel early-type hypersensitivity (ETH) reaction, manifested as capillary congestion, increase of vasopermeability, and plasma protein leakage, can be induced within 1 h after challenge of antigen-sensitized mice. The mediators involved in ETH varied among different strains of mice. The poly(Glu60Ala30Tyr10) (GAT)-induced ETH in BALB/c mice was blocked by diphenhydramine (histamine H1 antagonist) and ketanserine (serotonin antagonist), but not by cimetidine (histamine H2 antagonist). These results indicate that both histamine and serotonin are involved, and that the histamine effect is mediated through a H1 receptor. Meanwhile, GAT-induced ETH in B6 mice was inhibited by anti-TNF alpha antibody suggesting that TNF alpha is involved. The mice can be classified into either histamine or TNF alpha type based on the pattern of mediator involved in ETH. A/J and CBA strains as well as BALB/c mice were classified as histamine type while A. TL, B10.BR, and C3H/He in addition to B6 mice were TNF alpha type. The observation that GAT-induced ETH in (BALB/c x B6)F1 mice was inhibited by both diphenhydramine and anti-TNF alpha suggests that the mediation of the actions of histamine or TNF alpha by GAT was genetically controlled and inherited as the dominant trait in (BALB/c x B6)F1 mice. ETH could be passively transferred by heat (56 degrees C, 4 h)-treated anti-GAT sera. Sera derived from the histamine type transferred ETH across the type barrier and histamine was the mediator, irrespective of the type of the recipient. However, sera derived from TNF alpha type only transferred ETH to the mice of the same TNF alpha type and TNF alpha was the mediator.

The mixotope: a combinatorial peptide library as a T cell and B cell immunogen

We report a new approach in peptide vaccine strategy based on combinatorial synthesis. A library of 7.5 x 10(5) related peptides, termed mixotope, was derived from the sequence of the third hypervariable domain (V3 loop) of the human immunodeficiency virus (HIV) envelope protein. This preparation induced a strong immune response in all syngeneic and outbred rodents tested. The response directed against the mixotope included antibodies, CD4+ T helper cells (TH1 and TH2) and CD8+ T cells. In rodents immunized with the mixotope, the T cell response directed against individual V3 peptide sequences (BRU, MN, RF, SF2, and ELI) as measured by T cell proliferation and interleukin (IL)-2 production, was found to be major histocompatibility complex haplotype-dependent. However, additional experiments performed in mice indicated that selectivity was less restrictive when using IL-3 secretion to explore T cell activation. This combinatorial antigen could be considered as a series of agretopic motifs framing a multiplicity of closely related epitopes for T cell recognition and able to elicit a T cell and B cell repertoire. This new construct may therefore provide a basis for the design of future vaccine strategies.

Major histocompatibility complex regulation of T helper functions mapped to a peptide C terminus that controls ligand density

The functional status (Th1- versus Th2-like) of CD4 T cells primed against human collagen type IV (hCol IV) or a single 30mer peptide from the alpha 2 chain of this molecule is predicted by the major histocompatibility complex (MHC) class II (I-A) genotype of the responding mice. H-2s mice elicit Th1-like cell-mediated responses to these antigens, whereas Th2-like humoral responses are primed in H-2b,d,k mice. We now report that the ability of MHC to dictate T helper function in this system depends upon a single amino acid of the minimal alpha 2(IV) peptide. The C terminus of this minimal (12mer) peptide is -G-G-P-K, which is predicted to form a beta-turn. The present data demonstrate that the terminal lysine (K) stabilizes the immunogens full biological effects necessary for exclusive cell-mediated responses in H-2s mice. The lysine-truncated (11mer) peptide with otherwise identical sequence effectively primes T helper function in both H-2b and H-2s genotypes. Most importantly, our direct analysis of these peptides' presentation by live antigen-presenting cells (APC) reveals that the 12mer is bound at a log higher density on H-2s APC than on H-2b APC, and that the 11mer is presented at an equally low relative density on APC from both genotypes. In vitro analyses of 12mer/11mer cross-reactive Th clones demonstrate that I-As restricted clones require about 1-2 log lower doses of 12mer peptide than 11mer peptide to stimulate equivalent thymidine incorporation and cytokine release. By contrast, I-Ab-restricted (12mer/11mer cross-reactive) Th clones show no preference for the 12mer and require relatively high peptide doses similar to those required to stimulate the I-As clones with the 11mer peptide. Thus, the peptide dose requirements of Th clones reflect the high density of presentation associated with the 12mer: I-As ligand. Taken together, the results directly support the role of ligand density as an important control point in the functional decision of CD4 T cells.

Cathepsin D, but not cathepsin B, releases T cell stimulatory fragments from lysozyme that are functional in the context of multiple murine class II MHC molecules

In this study, the major endosomal/lysosomal proteases cathepsin D and cathepsin B were tested on their ability to release T cell stimulatory peptides from hen egg white lysozyme (HEL) in vitro. Whereas neither enzyme could cleave unreduced HEL under mild conditions, reduced HEL was readily cleaved by cathepsin D but not by cathepsin B. Instead, cathepsin B was found to be very active in the trimming of HEL peptides after their release by cathepsin D. Following high-performance liquid chromatography (HPLC) fractionation, cathepsin D-released HEL fragments were screened for recognition by HEL-specific T cells from three strains of mice, i.e. B10.A (H-2a), C57BL/6 (H-2b) and BALB/c (H-2d). Peptides in a large number of different HPLC fractions triggered significant T cell responses in all three strains. Interestingly, the response profiles of T cells from the three different strains showed marked similarities. Also, several individual synthetic HEL sequences corresponding to selected cathepsin D-released fragments were recognized by murine T cells in the context of all three major histocompatibility complex (MHC) haplotypes tested. Our data suggest that cathepsin D rather than cathepsin B may play a central role in the initial release of HEL fragments during endosomal/lysosomal processing. The relatively long HEL fragments released by cathepsin D, containing about 20-30 amino acid residues, are significantly more promiscuous in murine class II MHC binding than the shorter synthetic HEL sequences previously employed by others for the delineation of HEL epitopes. Extensive documentation of HEL epitopes in previous investigations indicate that this promiscuity cannot be explained by simply assuming that longer peptides contain additional epitopes. Rather, an increased peptide length by itself appears to promote promiscuous MHC binding.

Peptide specificity and HLA restriction do not dictate lymphokine production by allergen-specific T-lymphocyte clones

Human and murine CD4+ T lymphocytes can be subdivided into distinct subsets [T-helper type 0 (Th0), Th1 or Th2], based on their lymphokine production profiles. Not much is known about the factors that determine these restricted lymphokine secretion profiles. Peptide specificity and human leucocyte antigen (HLA) restriction may be such factors. As it is well established that allergen-specific T lymphocytes from atopic individuals and non-atopic controls differ in their lymphokine secretion profile, we studied two allergen-specific T-lymphocyte clones (TLC) with identical peptide specificity and HLA restriction that were generated from the peripheral blood of an atopic donor and a non-atopic control donor. The two CD4+ TLC recognize the same epitope (20-33) of the house dust mite Dermatophagoides pteronyssinus major allergen Der p II. Both TLC recognize the epitope in an HLA-DQB1*0602-restricted manner. However, the lymphokine production profiles of these TLC show clear differences after allergen-specific or polyclonal activation. As expected, TLC JBD4 from the atopic donor produced high levels of interleukin-4 (IL-4) without detectable interferon-gamma (IFN-gamma), whereas TLC PBA1 from the non-atopic donor produced both IFN-gamma and IL-4 upon allergen-specific or polyclonal activation. Inasmuch as both TLC recognized the same epitope of Der p II in association with the same HLA-DQ molecule, these data suggest that peptide specificity and HLA restriction of human allergen-specific TLC do not dictate their lymphokine secretion profile.

B cells are required for the switch from Th1- to Th2-regulated immune responses to Plasmodium chabaudi chabaudi infection

The induction of T-helper cell subsets during the course of blood stage Plasmodium chabaudi chabaudi infection was compared in immunologically intact NIH mice and mice that were depleted of B cells from birth by treatment with anti-mu antibodies. For intact mice, in which the acute primary parasitemia peaked 10 days following infection, purified splenic CD4+ T cells recovered during the ascending parasitemia produced high levels in vitro of interleukin 2 (IL-2) (peak levels on day 10) and gamma interferon (IFN-gamma) (peak levels on day 7). Sera collected from these mice at around this time contained relatively high levels of P. c. chabaudi-specific immunoglobulin 2a (peak levels on day 12), and serum nitric oxide activity was significantly elevated at peak parasitemia. During the descending primary parasitemia, production of IFN-gamma and IL-2 decreased, while levels of IL-4 and IL-10 produced by splenic CD4+ T cells were significantly raised from the time at which subpatency was recorded (day 17) and persisted for at least 50 days. This was concomitant with a significant increase in levels of parasite-specific immunoglobulin G1, which peaked at around the time of recrudescence. Thus, in normal mice, sequential appearance of Th1 and Th2 responses was observed. In contrast, in B-cell-depleted mice, recovery from acute primary parasitemia was followed by a persistent patent infection which did not drop below 0.1% for at least 75 days after initiation of infection. These mice were unable to mount a significant Th2 response, manifest as an enduring inability of splenic CD4+ T cells to produce significant levels of IL-4 and IL-10. IL-2 and IFN-gamma levels remained significantly elevated throughout the 50-day observation period, and there was sustained production of nitric oxide. These data show that immune responses mediated by CD4+ T cells of the Th1 subset are capable of limiting infection beyond the initial acute phase, but that they do not eliminate parasitemia. Furthermore, as the progression from a Th1-regulated to a Th2-regulated immune response fails to occur in B-cell-depleted mice, the data suggest that B cells are required for the downregulation of Th1-mediated and/or the generation of Th2-mediated protective immunity to P. c. chabaudi.

Inducible interleukin-4-secreting cells provoked in mice during chemical sensitization

It has been demonstrated previously that chemical contact and respiratory allergens differ with respect to the quality of immune responses they will provoke in mice. Trimellitic anhydride (TMA), a human respiratory allergen, induces in mice responses consistent with the preferential activation of Th2-type cells, resulting in the production of IgE anti-hapten antibody and an increase in the serum concentration of IgE. In contrast, oxazolone (OX), a potent contact allergen considered not to cause respiratory hypersensitivity, induces instead Th1-type responses in mice characterized by vigorous IgG2a antibody production and a failure to elicit IgE. In the present study we have extended these investigations and have examined the capacity of these chemicals to stimulate inducible interleukin-4 (IL-4) production by draining lymph node cells (LNC). IL-4 was measured in the supernatants of draining LNC cultured for various periods in the presence or absence of concanavalin A (Con A). Following primary topical exposure to the chemical allergens, Con A-stimulated LNC from OX-treated mice secreted significantly more IL-4 than did LNC from mice exposed to trimellitic anhydride (TMA). A different pattern of IL-4 secretion was observed following culture with Con A of LNC prepared from lymph nodes draining the sites of secondary exposure to these chemicals. In this case significantly higher concentrations of IL-4 were produced by TMA-treated mice. Detectable levels of IL-4 (> 300 pg/ml) were not found following culture of draining LNC from sensitized mice in the absence of Con A or following culture of LNC from naive mice with or without Con A. These data demonstrate that chemical allergens of different types stimulate discrete and changing patterns of inducible IL-4 synthesis consistent with the selective activation of Th-cell subpopulations.

The molecular basis of metal recognition by T cells

T lymphocytes play critical roles in a series of important immune responses, including delayed-type hypersensitivity and contact sensitivity. Metal haptens such as nickel are among the most common sensitizers. In general, T cells recognize fragments of proteins complexed to MHC molecules. Haptens, however, are too small to be antigenic by themselves. Recent experiments have suggested that hapten-specific T cells recognize hapten-modified MHC-peptide complexes. Here I review the data supporting this hypothesis and speculate on the relevance of these findings for the understanding of chemical-induced hypersensitivities.

IgE antibody responses induced by transplantation of the nematode Nippostrongylus brasiliensis in rats: a possible role of nematode excretory-secretory product in IgE production

In order to examine the effective site of sensitization for IgE responses, we transplanted 2000 adult-stage worms of the nematode Nippostrongylus brasiliensis into the duodenum or the peritoneal cavity of naive rats. Total serum IgE began to increase 1 week after the nematode inoculations and reached a peak at week 2. Living worms inoculated into the duodenum induced the highest serum IgE, this being 800 times the level in control animals. Intraperitoneal inoculations of living and dead worms resulted in increases of the serum IgE levels to 120 and 13 times the control level, respectively. The intraduodenal inoculation of living adult worms also induced a significant increase in specific IgE against the excretory-secretory (ES) product of adult N. brasiliensis 1 week later than the rise in total IgE, whereas intraperitoneal inoculations did not induce such an increase. These results suggest that sensitization through the intestinal mucosa with adult N. brasiliensis might be important for the effective induction of both specific and non-specific IgE responses. Since these findings also indicated that factors secreted by living worms play an important role in the induction of total IgE response, the ES product was injected to naive rats for 6 consecutive days (total 2.7-4.4 mg). Intraperitoneal injection of the ES product alone induced a 14.7-fold increase in total IgE without any specific IgE response. This indicates that some constituents of the ES product have the potential to trigger a non-specific IgE response.

The roles of cytokines produced in the immune response to the erythrocytic stages of mouse malarias

This review describes the role of cytokines produced by CD4+ T cells and macrophages in response to the erythrocytic stages of P. chabaudi chabaudi and other malaria infections in mice. Since virtually all compartments of the immune system are activated during the response against malaria, the variety of cytokines produced during infection is considerable. There is, however, a clear differential expression of different cytokines during primary infection. Th1-related cytokines are predominantly produced during the acute phase of infection, and lead mainly to the induction of macrophage-derived cytokines. This antibody-independent pathway is probably on the one hand, sufficient for parasite control early in infection via macrophage-associated inflammatory responses, but can, on the other hand, also lead to the pathological consequences of infection. As the infection progresses, the pattern of cytokine production shifts towards a Th2-like response. B cells play a crucial role in this process. A major consequence of this switch to a production of Th2-related cytokines later in infection would be the down-regulation of IFN-gamma-induced macrophage activation and the promotion of antibody production by mature B cells. This suggest that the mechanism of parasite control in the later stages of infection is predominantly antibody-dependent.

Major histocompatibility complex regulation of interleukin-5 production in the mouse

Lymph node cells of CBA (H-2k), but not of BALB/c (H-2d) mice immunized epicutaneously with picryl chloride secrete interleukin (IL)-5 when stimulated with the specific antigen in vitro. The low IL-5 production in BALB/c mice persists when either picryl chloride or the unrelated antigen oxazolone are used, when the amount of antigen in vitro is varied and when a secondary response is studied. The difference in IL-5 production maps to the major histocompatibility complex (MHC) in the congenic BALB/b, BALB/c and BALB/k mice. Furthermore, lymph node cells from (k x d) F1 mice produce IL-5 when stimulated by antigen presented on H-2k but not on H-2d antigen-presenting cells. Finally, the low IL-5 production in vitro in BALB/c mice is correlated with low picryl-specific IgA levels in vivo, which otherwise are ten times greater in CBA and BALB/k mice. The influence of MHC on IL-5 production and IgA secretion in the mouse might be a possible basis for the association of MHC with IgA deficiency in humans.

Influence of the antigen delivery system on immunoglobulin isotype selection and cytokine production in response to influenza A nucleoprotein

The influence of different antigen delivery systems on antibody isotype and lymphokine profile has been investigated using influenza nucleoprotein as a model antigen system. Mice exposed to live or inactivated influenza virus produced antibody against whole virus or recombinant nucleoprotein (rNP), which was predominantly of the IgG2a isotype. Spleen or lymph node cells from these mice rapidly produced large amounts of interferon-gamma (IFN-gamma), but no detectable interleukin-5 (IL-5) when stimulated in vitro with specific antigen. In contrast, after primary immunization with rNP or p206-229 in different adjuvants (CFA, quil A or alhydrogel), specific antibody was predominantly of the IgG1 isotype and relatively lower amounts of IFN-gamma but no IL-5 were detected following in vitro antigenic stimulation. Secondary immunization, however, resulted in detection of IgG2a antibodies and increased levels of IFN-gamma. IL-5 was only detected after secondary immunization with peptide in adjuvant. Mice infected with aro A- Salmonella typhimurium expressing NP produced antibody of both IgG1 and IgG2a isotypes and large amounts of IFN-gamma and no IL-5, following in vitro antigenic stimulation, and therefore parallelled the pattern seen with whole virus more closely than that seen following primary immunization with protein or peptide in conventional adjuvants. The results suggest that the antigen delivery vehicle influences both quantitative and qualitative differences in the type of immune response elicited, which may be important in determining the potency of protective immunity induced.