Regulation of T helper cell cytokine expression: functional dichotomy of antigen-presenting cells

Immunoregulation of malarial infection: balancing the vices and virtues

Malaria continues to extract an incalculable cost on human morbidity and mortality throughout tropical and subtropical regions of the world, and effective control measures are urgently needed. Despite considerable efforts in recent years to develop subunit vaccines targeted at various stages of the Plasmodium life-cycle, the commercial availability of a vaccine is still a distant prospect. One of the underlying difficulties hindering successful vaccine design is our incomplete knowledge of the precise type(s) of immune response to aim for, and then how to achieve it. A greater appreciation of the mechanisms of protective immunity, on the one hand, and of immunopathology, on the other, should provide critical clues on how manipulation of the immune system may best be achieved. Ten years have passed since the identification of the Th1/Th2 paradigm for distinguishing CD4+ T cells according to cytokine secretion patterns which determine their function. This review summarises our progress towards understanding the broad spectrum of immune responsiveness to the blood stages of the malaria parasite during experimental infections in mice and highlights the way in which examination of rodent malarias provides a powerful tool to dissect the interaction of Th1 and Th2 cells during an immune response to an infectious disease agent. It is proposed that the pliability of rodent systems for investigating immunoregulation provides valuable insight into the balance between protection and pathology in human malaria and throws light on the factors involved in the modulation of vaccine-potentiated immunity.

Induction of T1 (cytotoxic lymphocyte) and/or T2 (antibody) responses to a mucin-1 tumour antigen

Effective vaccination-based control of intracellular pathogens or parasites and various tumours is dependent upon induction of cytotoxic lymphocytes and other mechanisms of cellular immunity. Such responses are usually described as being antagonistic to an antibody-based immune response. This paper elaborates on previous studies that have demonstrated that conjugation of a fusion protein (FP, incorporating copies of the variable number of tandem repeat sequence of human mucin-1 (MUC1)) to oxidized mannan results in a significant shift from a type-2 response towards a type-1 response. This response induces complete protection upon challenge of immunized mice with MUC1 expressing tumour cells. This report details experiments in which the balance between type-1 and type-2 anti-MUC1 responses is manipulated by altering the dose of mannan-FP (M-FP) delivered. It is also shown that type-1 and type-2 responses may be induced simultaneously by administration of both forms of the antigen (FP/M-FP). Further, when a type-2 response is induced after FP immunization, a type-1 response can also be established by subsequent immunization with M-FP without adversely affecting the initial response. The converse also applies when M-FP is used for the initial immunizations, followed by FP administration. Delivery of interleukin-1 beta as a cytokine adjuvant with M-FP immunizations also enhanced antibody responses to levels fourfold that induced by M-FP alone without adversely affecting the cytotoxic activity induced by M-FP immunization. Contrary to the type-1/type-2 paradigm, cellular and antibody responses to MUC1 were not antagonistic. These results have important implications for the development of vaccination strategies against pathogens for which both the cellular and humoral compartments of the immune response contribute to protection.

Lipopeptides of Borrelia burgdorferi outer surface proteins induce Th1 phenotype development in alphabeta T-cell receptor transgenic mice

Induction of the appropriate T helper cell (Th) subset is crucial for the resolution of infectious diseases and the prevention of immunopathology. Some pathogens preferentially induce Th1 or Th2 responses. How microorganisms influence Th phenotype development is unknown. We asked if Borrelia burgdorferi, the spirochete which causes Lyme arthritis, can promote a cytokine milieu in which T cells which are not specific for B. burgdorferi are induced to produce proinflammatory cytokines. Using alphabeta T-cell receptor transgenic mice as a source of T cells with a defined specificity other than for B. burgdorferi, we found that B. burgdorferi induced Th1 phenotype development in ovalbumin-specific transgenic T cells. Small synthetic lipopeptides corresponding to the N-terminal sequences of B. burgdorferi outer surface lipoproteins had similar effects. B. burgdorferi and its lipopeptides induced host cells to produce interleukin-12. When the peptides were used in delipidated form, they did not induce Th1 development. These findings may be of pathogenic importance, since it is currently assumed that a Th2-mediated antibody response is protective against B. burgdorferi. Bacteria associated with reactive arthritis, namely, Yersinia enterocolitica, Shigella flexneri, and Salmonella enteritidis, had different effects. The molecular definition of pathogen-host interactions determining cytokine production should facilitate rational therapeutic interventions directing the host response towards the desired cytokine response. Here, we describe small synthetic molecules capable of inducing Th1 phenotype development.

Infection with Salmonella typhimurium modulates the immune response to Schistosoma mansoni glutathione-S-transferase

Immune response polarization is controlled by several factors, including cytokines, antigen-presenting cells, antigen dose, and others. We have previously shown that adjuvants and live vectors play a critical role in polarization. Thus, immunization with the Schistosoma mansoni 28-kDa glutathione-S-transferase (Sm28-GST) in aluminum hydroxide induced a type 2 cytokine profile and the production of immunoglobulin G1 (IgG1)- and IgE-specific antibodies. In contrast, mice infected with recombinant Salmonella typhimurium expressing Sm28-GST developed a type 1 cytokine profile and produced IgG2a-specific antibodies against Sm28-GST and Salmonella antigens. In this study, to determine if S. typhimurium not expressing Sm28-GST would still influence the type of the response against this antigen, we compared the profiles of the immune responses generated against Sm28-GST administered in alum in mice infected and not infected with S. typhimurium. Infected mice generated both IgG1 and IgG2a antibodies against Sm28-GST, while noninfected mice produced only IgG1 anti-Sm28-GST antibodies. Moreover, interleukin-4 (IL-4) mRNA expression in infected mice was near background levels, while gamma interferon (IFN-gamma) mRNA expression in coinfected mice was significantly higher than in mice immunized with Sm28-GST in alum only. However, after antigen-specific stimulation in vitro with Sm28-GST, levels of IL-4 and IFN-gamma cytokine production were similar in the two groups of mice. These results suggest that (i) the immune milieu produced during an infection may modify the response against an irrelevant antigen and (ii) isotype switching may be influenced by the cytokine environment of a bystander immune response, even though the specific antigen-driven cytokine production is not modified. Thus, the isotypic profile is not always an absolute reflection of the cytokines produced by antigen-specific Th cells.

Neonates at risk of atopy show impaired production of interferon-gamma after stimulation with bacterial products (LPS and SEE)

Recent studies demonstrate reduced interferon-gamma (IFN-gamma) secretion in neonates who became atopic later in life. The underlying pathomechanism is still unknown. We therefore examined the effects of bacterial products on neonatal IFN-gamma production acting through different T-cell- or antigen-presenting-cell (APC)-stimulating mechanisms: cord-blood mononuclear cells (CBMC) were incubated with lipopolysaccharide (LPS), staphylococcal enterotoxin E (SEE), or a combination of both and restimulated with PMA and ionomycin. LPS and SEE as single stimuli induced IFN-gamma production to the same extent in CBMC of neonates with high and low risk of atopy. In contrast, a combination of LPS and SEE had a multiplying effect on IFN-gamma secretion only in CBMC of neonates with low risk of atopy. Phenotype analysis revealed that only memory T cells showed impaired IFN-gamma synthesis (median 3.6% IFN-gamma-producing cells vs 14.2% in controls: P < 0.01), whereas IFN-gamma production by naive T cells did not differ in either group. Taken together, these results point to the existence of a disturbed function of costimulatory mechanisms in neonates at high risk of atopy, provoking reduced memory T-cell IFN-gamma production.

CD45RA-expressing memory/effector Th cells committed to production of interferon-gamma lack expression of CD31

It has been considered before that human naive and memory/effector CD4+ T-cells cannot be subdivided solely according to the differential expression of CD45 isoforms. By the lack of expression of CD31 we have identified a subset of CD4+ CD45RA+ CD31- cells which show distinct features of antigen-experienced Th1 cells. Short term stimulation of highly purified human peripheral blood CD4+ T-cells with PMA/ionomycin, followed by the cytometric analysis of intracellular cytokines, showed that a minor subpopulation of CD4+ CD45RA+ CD45RO- cells is able to produce interferon-gamma (IFN-gamma) rapidly, a characteristic of antigen-experienced Th1 cells. Whereas among CD45RA+ CD4+ T-cells both CD31+ and CD31- subsets produce interleukin-2 (IL-2) upon PMA/ionomycin stimulation, only the CD31- subpopulation is able to produce IFN-gamma. Thus, our phenotypic and functional characterization of CD45RA+ CD45RO- Th cells shows that CD45RA+ CD45RO- cells do not represent a homogeneous population of antigen-unexperienced, naive T-cells. We speculate that a certain subset of human CD4+, CD45RO+ memory T-cells reverts to expression of the CD45RA isoform, and that this subset can be identified by the lack of CD31 expression.

Immunocytochemical and flow cytofluorimetric detection of intracellular IL-4, IL-5 and IFN-gamma: applications using blood- and airway-derived cells

We have compared an immunocytochemical and a flow cytofluorimetric method to detect intracellular IFN-gamma, IL-4 and IL-5 in T-cell clones, peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage fluid (BALF) cells. Intracellular bound cytokine-specific antibodies were visualized either with amino-ethyl carbazole (for immunocytochemistry), or with fluorescent antibodies (for flow cytofluorimetry). The staining was inhibited with recombinant cytokines and corresponded qualitatively and quantitatively to cytokine levels in the supernatants of T-helper-0 (Th0), Th1 and Th2 clones. In analysing in vitro stimulated cells, sufficient signal in the fluorimetric assay was only obtained after the addition of monensin to the cultures. We then observed a good correlation between immunocytochemical (with no monensin added) and the flow cytofluorimetric staining for all three cytokines (PBMC, IFN-gamma and IL-4, rho = 0.9, no IL-5 detectable; clones, IL-5, rho = 0.81, all three p < 0.05). However, compared to flow cytometry, a greater percentage of positively stained cells was frequently observed using immunocytochemistry. In BALF cells, the immunocytochemical method was able to detect significant percentages of positive cells without in vitro stimulation of the cells, in contrast to the flow cytofluorimetric method. In BALF cells from sarcoidosis patients, T-cells were mainly IFN-gamma-positive (immunocytochemically assessed), both with (mean +/- SEM, 39.7 +/- 9.8%), and without (3.5 +/- 1.3%) in vitro stimulation. In BALF cells from allergic subjects, the immunocytochemical method showed lymphocytes positive for IFN-gamma (40.3 +/- 8.3%), IL-4 (19.1 +/- 0.49) and IL-5 (6.1 +/- 3.1). We conclude that both methods can be used to assess the production of IFN-gamma, IL-4 or IL-5 at the single-cell level in T-cell clones, PBMC and cells from the BALF. The high sensitivity and the low number of cells required for the immunocytochemical method indicate that this method can provide detailed information on cytokine production of airway-derived cells in diseases with airway inflammation such as sarcoidosis and asthma.

Polymorphic MHC class II promoters exhibit distinct expression pattern in various antigen-presenting cell lines

The promoter regions of MHC class II genes are characterized by the presence of conserved sequence motifs called S,X and Y boxes, which are crucial for regulation of transcription of these genes. In humans, promoter polymorphism is known to result in differential transcriptional activity at both inter-locus and inter-allelic levels, but it is not yet known how this relates to tissue-specific expression of MHC class II molecules. We sequenced the 5' regulatory regions of alpha and beta genes of I-A and I-E molecules from four mouse haplotypes and found allelic polymorphisms which were mainly confined to the X box. The promoter sequences of I-Ea genes were non-polymorphic. Transfection of four antigen-presenting cell types with promoter-reporter gene constructs revealed that the promoter sequence polymorphisms result in distinct allele- and tissue-specific activity patterns. Mutagenesis experiments in which the X2 box was reshuffled between I-A beta alleles demonstrated that this box contributes to regulation of differential MHC class II expression in the four cell types. The possibility is discussed that tissue-specific MHC class II expression may control differentiation of T-cell subsets.

Functional significance of polymorphism among MHC class II gene promoters

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

Type 1 and type 2 cytokine dysregulation in human infectious, neoplastic, and inflammatory diseases

In the mid-1980s, Mosmann, Coffman, and their colleagues discovered that murine CD4+ helper T-cell clones could be distinguished by the cytokines they synthesized. The isolation of human Th1 and Th2 clones by Romagnani and coworkers in the early 1990s has led to a large number of reports on the effects of Th1 and Th2 on the human immune system. More recently, cells other than CD4+ T cells, including CD8+ T cells, monocytes, NK cells, B cells, eosinophils, mast cells, basophils, and other cells, have been shown to be capable of producing "Th1" and "Th2" cytokines. In this review, we examine the literature on human diseases, using the nomenclature of type 1 (Th1-like) and type 2 (Th2-like) cytokines, which includes all cell types producing these cytokines rather than only CD4+ T cells. Type 1 cytokines include interleukin-2 (IL-2), gamma interferon, IL-12 and tumor necrosis factor beta, while type 2 cytokines include IL-4, IL-5, IL-6, IL-10, and IL-13. In general, type 1 cytokines favor the development of a strong cellular immune response whereas type 2 cytokines favor a strong humoral immune response. Some of these type 1 and type 2 cytokines are cross-regulatory. For example, gamma interferon and IL-12 decrease the levels of type 2 cytokines whereas IL-4 and IL-10 decrease the levels of type 1 cytokines. We use this cytokine perspective to examine human diseases including infections due to viruses, bacteria, parasites, and fungi, as well as selected neoplastic, atopic, rheumatologic, autoimmune, and idiopathic-inflammatory conditions. Clinically, type 1 cytokine-predominant responses should be suspected in any delayed-type hypersensitivity-like granulomatous reactions and in infections with intracellular pathogens, whereas conditions involving hypergammaglobulinemia, increased immunoglobulin E levels, and/or eosinophilia are suggestive of type 2 cytokine-predominant conditions. If this immunologic concept is relevant to human diseases, the potential exists for novel cytokine-based therapies and novel cytokine-directed preventive vaccines for such diseases.

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.

The production of immunoregulatory cytokines is localized to the extrafollicular area of human tonsils

The localization and production at the single cell level of 19 different human cytokines, IL-1 alpha, IL-1 beta, IL-1ra, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, IL-13, TNF alpha, TNF beta, IFN gamma, GM-CSF, G-CSF, and TGF beta 1-3, were studied in cryopreserved tonsillar tissue using immunohistochemical staining. The cytokine producing cells, with the exception of IL-1 expressing cells, had a characteristic morphology due to the accumulation of cytokine onto the Golgi organelle. The production of each cytokine was localized to specific compartments in tonsillar tissue sections from children with tonsillar hypertrophy or recurrent tonsillitis in the resting state. Immunoregulatory cytokines such as IL-2, IL-3, IL-4, G-CSF, GM-CSF and TGF beta were produced in the extrafollicular area and entrapped on the cell membranes as well as in pudels in the extracellular matrix surrounding the producer cells. The dominating cytokines both in tissues from recurrent tonsillitis and tonsillar hypertrophy were GM-CSF, G-CSF, and TGF beta 1-3 which were synthezised predominantly in the reticular crypt site. IL-1 alpha, beta and IL-1ra, on the other hand, were localized to the surface and crypt epithelium and to scattered regions in the extrafollicular area. IL-2, IL-6, IFN gamma and IL-10 were found much more often in sections obtained from recurrent tonsillitis tissue compared with those from tonsillar hypertrophy. Reversely, an excessive production of IL-4 was noted in tonsillar hypertrophy compared with that in recurrent tonsillitis. Thus, concomitant production of multiple cytokines was evident with similarities but also differences in cytokine pattern between the two groups studied. The data suggest that T-cell mediated B-cell activation and differentiation take place in the extrafollicular area. Children with recurrent tonsillitis had a higher amount of B-cells and monocytes compared with children with tonsillar hypertrophy. However, the number of CD3, CD4, CD8 or cytoplasmic Ig-positive cells did not differ between the two groups.

Induction of differential T-helper-cell responses in mice infected with variants of the parasitic nematode Trichuris muris

The resistance or susceptibility of mice to infection with the intestinal nematode parasite Trichuris muris is closely correlated with polarization of T helper (Th) cell responses to the type 2 (Th2) or type 1 (Th1) subset. Comparison of infections with three isolates of T. muris (E/K, E/N, and S) in three inbred strains of mice (CBA, C57BL/10, and B10.BR) has shown that host Th response phenotype can be parasite determined. Although the mouse strains used show genetically determined variation in ability to respond to T. muris (CBA > C57BL/10 > B10.BR), the speed of worm expulsion in a given strain depended upon the isolate used for infection (E/K > E/N > S). The two isolates that induced the most effective resistance (E/K and E/N) elicited parasite-specific host antibody responses that were dominated by immunoglobulin G1 (IgG1), and antigen-stimulated T cells from infected mice released interleukin-5 in vitro. With the isolate that induced the least host resistance (S), the dominant antibody response was IgG2a, and T cells released gamma interferon in vitro. These data show clearly that parasite variant-specific factors play a major role in Th subset polarization during infection.

Specific expression of surface interferon-gamma on interferon-gamma producing T cells from mouse and man

Interferon (IFN)-gamma is a potent immunoregulatory protein secreted by CD4+ and CD8+ T cells and by natural killer cells. Here, we show that IFN-gamma is specifically displayed at a low concentration on the cell surface of those activated T cells from mouse and man which express IFN-gamma. It is transiently expressed on the cell surface with kinetics similar to those of intracellular IFN-gamma expression. Detectable surface IFN-gamma is not expressed by activated T helper (Th) cells producing other cytokines but which do not express IFN-gamma. Thus, surface IFN-gamma is the first available marker for live T lymphocytes expressing IFN-gamma, e.g. Th1 cells.

Dendritic cell presentation of PPD and 19 kDa protein of Mycobacterium tuberculosis and emergent T helper cell phenotype

Protection against infection with Mycobacterium tuberculosis is preferentially associated with the development of the T helper 1 subset, IFN-gamma production and a cell-mediated response, rather than with T helper 2 cells, 4 (IL-4) and antibody production. The type of APC interacting with T cells responsive to mycobacterial peptides may influence which of these responses predominates. This investigation focuses on the role of dendritic cells (DC) because they are the most potent APC in both primary and recall immune responses. Our results show that splenic DC-enriched suspensions prepared from C57BL/6 mice and pulsed with either purified protein derivative (PPD) or the immunodominant 19 kDa protein from M. tuberculosis, can activate antigen-primed T cells in vitro, whereas spleen cell suspensions depleted of DC cannot. DC pulsed with PPD or 19 kDa antigen are able to prime naive T cells in vivo. Supernatants collected from cultures containing T cells from mice injected with PPD-pulsed DC and then challenged in vitro with PPD-pulsed DC were found to contain more IL-2 and IFN-gamma than those from control mice which received either DC or PPD alone. No such antigen-specific IFN-gamma response occurred if DC pulsed with 19 kDa were used in place of PPD-pulsed DC. IL-4 was not detected in any of the culture supernatants. We conclude that DC can induce production of cytokines associated with a protective immune response when presenting peptides derived from heterogeneous mycobacterial antigens but not when exposed to the single 19 kDa immunodominant protein.

Role and modulation of T-cell cytokines in allergy

Allergic sensitization and the development of effector functions are controlled by IL-4-secreting and IL-5-secreting type 2 T cells. Recent studies have provided new insights into the events triggering the development of type 1 and type 2 T cells, the discrimination of type 1 and type 2 effector T cells from various T-cell subsets, and the improvement of established and new therapeutic strategies, which are aimed at modulating such T-cell functions in the allergic patient.

Heterogeneity of intracellular cytokine synthesis at the single-cell level in polarized T helper 1 and T helper 2 populations

CD4+ T helper (Th) cells can be classified into different types based on their cytokine profile. Cells with these polarized patterns of cytokine production have been termed Th1 and Th2, and can be distinguished functionally by the production of IFN-gamma and IL-4, respectively. These phenotypes are crucial in determining the type of immune response that develops after antigen priming. There are no surface markers that define them, and cytokine immunoassay or mRNA analysis both have limitations for characterization of single cells. Using immunofluorescent detection of intracellular IFN-gamma and IL-4, we have studied the emergence of Th1 and Th2 cells in response to antigen exposure and the patterns of cytokine synthesis in established T cell clones. IFN-gamma production by Th1 clones was detectable in almost all cells by 4 h, and it continued in most cells for > 24 h. IL-4 production in Th2 cells peaked at 4 h, but declined rapidly. In Th0 cells containing both cytokines, fewer cells produced IFN-gamma, which did not appear until IL-4 synthesis declined. Cocultivation of clones showed no such cross-regulation. Antigen stimulation of transgenic T cells expressing an ovalbumin-specific T cell receptor generated Th2 cells, probably as a result of endogenous IL-4 production. Addition of IL-12 and/or anti-IL-4 caused Th1 cells to develop, while some Th0 cells were seen when IL-12 alone was added. These results show that stimulation in the presence of polarizing stimuli results in cells producing either IFN-gamma or IL-4, but that coproduction can occur in rare cells under defined conditions.

Enhancement of endotoxin-induced interleukin-10 production by SR 31747A, a sigma ligand

SR 31747A is a new sigma ligand eliciting immunosuppressive and anti-inflammatory properties. Here, we show that SR 31747A greatly enhances lipopolysaccharide (LPS)-induced systemic release of interleukin (IL)-10, while it inhibits the secretion of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. In line with this finding, we also show by using quantitative reverse transcription-polymerase chain reaction analysis that SR 31747A increased LPS-induced IL-10 mRNA accumulation in spleen cells, whereas the level of both TNF-alpha and IFN-gamma mRNA was dramatically decreased. The enhancement of IL-10 production by SR 31747A treatment was also apparent in nude and severe-combined immunodeficient mice treated with LPS, clearly indicating that T and B cells were not involved. Finally, SR 31747A conferred protection against the lethal effect of LPS. The finding that SR 31747A strongly stimulates the synthesis of the natural anti-inflammatory cytokine IL-10, a property not observed with dexamethasone, provides new insights for the clinical use of this original compound, particularly in chronic inflammatory diseases where IL-10 is believed to be a pivotal regulatory component.

The immune response to cytochrome c in BALB/c mice is delayed due to inability of their non-specific antigen-presenting cells to provide its immunodominant epitope

The antibody response to horse cytochrome c (cyt.c) in BALB/c mice developed slowly and a substantial production of IgG antibodies was observed only 26-30 days after immunization. Lymph node cells (LNC) of unimmunized mice proliferated weakly in response to both native cyt.c and its synthetic peptides. On day 8 after immunization, LNC could not be stimulated with native cyt.c and peptide 92-104. However, they did proliferate in response to cyt.c peptides 1-6, 1-13, 2-13, 14-22, 46-56, 57-77, 61-77 and 61-69 which are closely related in horse and mouse cyt.c. On day 26, both native cyt.c and the peptides, including 92-104, were equally active in stimulating LNC proliferation. Both plastic-adherent and cyt.c-specific cells panned from day 8 cells enhanced the response of unprimed cells to native cyt.c. Elimination of B cells demonstrated that primary recognition of cyt.c was mediated, at least partly, by non-specific antigen-presenting cells (APC) while later B cells of additional specificities were involved. It is concluded that immunization with horse cyt.c initiated an autoimmune response resulting in T-dependent anergy. Peptide determinants processed by non-specific APC stimulated corresponding autoreactive T cells. Specific B cells which appeared as a result of the response maturation processed successfully the immunodominant epitope and finally mediated proliferative and antibody responses.

Identification of thyroid stimulating hormone receptor-specific T cells in Graves' disease thyroid using autoantigen-transfected Epstein-Barr virus-transformed B cell lines

The importance of thyrotropin receptor (TSHR) agonist antibodies in the manifestations of Graves' disease (GD) is recognized. There are, however, no convincing reports of TSHR-specific T cells. We have previously cloned T cells specific for thyroglobulin and thyroid peroxidase (TPO) from GD lymphoid infiltrates and used autologous EBV-transformed B cell lines (EBVL) transfected with an expression vector encoding TPO to efficiently detect TPO-specific T cells. Here we used EBVL transfected with TSHR to seek TSHR-specific T cells in the GD infiltrates, after cloning the in vivo activated T cells without antigen. 3 out of 30 clones responded vigorously and reproducibly to EBVL-TSHR, with a mean stimulation index > 7. Their release of IL-2, IL-4, and IL-10 after stimulation with soluble anti-CD3 and phorbol ester was indistinguishable from the other clones from this thyroid. However, they produced relatively little IFN gamma (median IL-4/IFN gamma ratio of 0.80) compared with the other clones (median IL-4/IFN gamma ratio 0.06). Thus, this new potent method of antigen presentation, using autoantigen-transfected EBVL, has permitted the first unequivocal identification of TSHR T cells in GD thyroid, with distinct Th0/Th2 characteristics, unlike previously cloned TPO-responsive cells which have Th1 characteristics.

Towards a vaccine against asexual blood stage infection by Plasmodium falciparum

In this paper, we will summarize the progress obtained in the malaria vaccine project developed by the Institut Pasteur groups interacting through the International Network of Pasteur Institutes over the last fifteen years. While trying to follow the progress in scientific and technological concepts and methodologies, the basic approach was still essentially the same as that followed by Pasteur and his acolytes to try to artificially reproduce the natural processes that lead to the development of immunity to infection and disease. A longitudinal study of two villages from the Sine Saloum area of Senegal, Dielmo and N'Diop, conducted in recent years by teams of the Institut Pasteur of Dakar, Senegal, in collaboration with the local ORSTOM malaria unit has led to the detailed analysis of the natural acquisition of premunition against Plasmodium falciparum malaria in endemic areas. The Saimiri model developed at the Pasteur Institute in Cayenne, was an important step forward in terms of studies on the mechanisms of action of protective antibodies and on vaccinations assays. If we accept the conclusions of the Pasteur groups' research on the experimental primate model and on the development of natural immunity (premunition) in highly endemic areas, the main inhibitor of progress in vaccine development is our poor understanding of the regulation of the immune response. Therefore, the general approaches that were followed for vaccine development must now be further explored using the continually developing tools of immunology and molecular biology, to elucidate regulations of the immune responses to the parasite, and identify the molecular mechanisms used by the parasite to generate and change antigen specificities.

Characteristic cytokines generated by keratinocytes and mononuclear infiltrates in oral lichen planus

Cytokine production was investigated in oral keratinocytes and tissue-infiltrated mononuclear cells (TIMC) obtained from patients with oral lichen planus (OLP). The numbers of cells producing interleukin (IL)-1 beta, IL-4, IL-6, granulocyte colony-stimulating factor, and tumor necrosis factor-alpha per 10(4) cells in keratinocytes from patients with OLP were determined by enzyme-linked immunospot assay. These levels were two to threefold greater than those in keratinocytes from chronically inflamed gingiva and 10 to 20-fold of those from the intact gingiva. The concentrations of these cytokines in the culture supernatants of keratinocytes were correlated with the number of cytokine-producing cells. Compared with TIMC in the gingiva and peripheral blood mononuclear cells, TIMC in OLP were more cytokine-productive, with larger numbers of cytokine-producing cells that expressed more cytokine messengers. More IL-6, IL-2, and IL-10 were generated from TIMC in OLP, whereas less granulocyte colony-stimulating factor was generated. After pretreatment with IL-2, TIMC from OLP patients generated more IL-6 than did peripheral blood mononuclear cells, and IL-4-pretreated TIMC from the patients released larger amounts of IL-2, IL-6, and IL-10. These results indicate that keratinocytes play a critical role in OLP through production of large amounts of cytokines, that TIMC are stimulated in situ and differentiated to produce cytokines characteristic of OLP, and that the inflammatory condition of OLP is determined by the local cytokine network.

Regulatory cellular interactions in the primary mixed lymphocyte reaction

Limiting dilution analysis (LDA) of allogeneic and syngeneic murine mixed lymphocyte reactions was used to study the heterogeneity both of the responding spleen cells and of the stimulating antigen-presenting dendritic cells (DC). In contrast with traditional LDA of single-hit processes, a non-linear dependence of the proportion of negative microcultures on responding spleen cell concentration was obtained. The non-linearity of this LDA plot was interpreted as being the result of a competitive interaction between two types of limiting precursor cells. The regulatory and stimulatory functions of DC were investigated in the same LDA systems by testing various levels of DC from spleen or thymus as limiting cells in the presence of a constant quantity of syngeneic splenic responder T cells. This revealed a functional heterogeneity amongst DC, which were found to suppress proliferation of responder cells at low DC levels but to stimulate proliferation at higher levels. At levels where splenic DC became stimulatory, thymic DC remained suppressive.

The immunopathology of chronic inflammatory periodontal disease

Chronic inflammatory periodontal disease is known to be under the control of the immune response. However, the precise mechanism of the immunopathogenesis of this lesion has not yet been fully elucidated. In this review, the regulatory role of both lymphoid and non-lymphoid cells as well as cytokines and accessory molecules in the course of chronic inflammatory periodontal disease is discussed. Finally, based upon previous evidences, an attempt to establish a model of chronic inflammatory periodontal disease is made herein.

Persistence of local cytokine production in shigellosis in acute and convalescent stages

Shigella infection is accompanied by an intestinal activation of epithelial cells, T cells, and macrophages within the inflamed colonic mucosa. A prospective study was carried out to elucidate the cytokine pattern in Shigella infection linked to development of immunity and eradication of bacteria from the local site and also to correlate the cytokine profile with histological severity. An indirect immunohistochemical technique was used to determine the production and localization of various cytokines at the single-cell level in cryopreserved rectal biopsies from 24 patients with either Shigella dysenteriae type 1 (n = 18) or Shigella flexneri (n = 6) infection. The histopathological profile included presence of chronic inflammatory cells with or without neutrophils and microulcers in the lamina propria, crypt distortion, branching, and less frequently crypt abscesses. Patients had significantly higher (P < 0.005) numbers of cytokine producing cells for all of the cytokines studied, interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-1ra, tumor necrosis factor alpha (TNF-alpha), IL-6, IL-8, IL-4, IL-10, gamma interferon, TNF-beta, and transforming growth factor beta 1-3, in the biopsies than the healthy controls (n = 13). The cytokine production profile during the study period was dominated by IL-1 beta, transforming growth factor beta 1-3, IL-4, and IL-10. Significantly increased frequencies of cytokine-producing cells (P < 0.05) were observed for IL-1, IL-6, gamma interferon, and TNF-alpha in biopsies with severe inflammation in comparison with those with mild inflammation. During the acute stage of the disease, 20 of 24 patients exhibited acute inflammation in the rectal biopsies and the cellular infiltration was still extensive 30 days after the onset of diarrhea, although the disease was clinically resolved. In accordance with the histological findings, cytokine production was also upregulated during the convalescent phase; there was no significant difference (P > 0.05) in the incidence of cytokine-producing cells between acute (2 to 8 days after the onset of diarrhea) and convalescent (30 days after onset) stages.

Tolerance to staphylococcal enterotoxin B initiated Th1 cell differentiation in mice infected with Candida albicans

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that specifically activates T cells bearing V beta 8 T-cell receptor domains, which eventually leads to a long-lasting state of clonal anergy accompanied by selective cell death in the targeted CD4+ subset. Because the superantigen is known to promote Th1 cell differentiation in vitro, we have investigated the effect of SEB treatment on the course of Th2-associated progressive disease in mice infected systemically with Candida albicans. On the basis of the kinetics of SEB-induced changes in CD4+ cells and production in sera of interleukin 4 (IL-4), IL-10, and gamma interferon, we obtained evidence that V beta 8+ cell anergy concomitant with infection abolished the early IL-4/IL-10 response of the host to the yeast, ultimately leading to a state of resistance characterized by gamma interferon secretion in vitro by antigen-specific CD4+ cells. In contrast, SEB administered near the time of challenge resulted in accelerated mortality. Significant resistance to infection was also afforded by exposure of mice to a retrovirally encoded endogenous superantigen. These data suggest that CD4+ V beta 8+ T cells play an important role in vivo in the initiation of a Th2 response to C. albicans and that suppression of their activity may alter the qualitative development of the T-cell response and the outcome of infection.

A dual role for B cells in Plasmodium chabaudi chabaudi (AS) infection?

CD4+ T cells are necessary for a protective immune response against the erythrocytic stages of the malaria parasite Plasmodium chabaudi chabaudi AS. B cells are not required for control of early acute parasitaemias, but appear to be important for final clearance of the infection, most probably by producing specific antibodies against the parasite. However, immune sera and immune IgG are unable to replace the protective capacity of B cells in adoptive transfer of immunity to P. chabaudi AS. It is therefore conceivable that B cells are required to achieve protective immunity, not only as effector plasma cells, but because they may also play a second important role. We have recently suggested that B cells may regulate the Th response to P. chabaudi AS during a primary infection. We discuss here the possibility of a dual requirement of B cells in achieving protective immunity to P. chabaudi AS.

Immunoglobulin isotype regulation by antigen-presenting cells in vivo

The isotype and magnitude of the B cell response clearly depends on the in vivo activation of T helper (Th) cells which secrete different lymphokines. Since Th are activated by the presentation of the antigen on specialized cells, we wished to test whether the nature of the antigen-presenting cells (APC) influences the isotypic profile of the humoral response. Data are presented showing that antigen-pulsed dendritic cells (DC) and peritoneal macrophages induce the synthesis of specific antibodies when injected in syngeneic animals. By contrast, a single injection of antigen-pulsed resting B cells does not prime the mice in vivo. Moreover, the injection of antigen-pulsed DC induces the synthesis of specific IgG2a and IgG1 antibodies, whereas peritoneal macrophages favor the production of IgG1 and IgE antibodies specific for the antigen. These data show that the isotype and the amplitude of the B cell response can be regulated by the nature of the APC, and indirectly suggest that Th cell differentiation is controlled at the level of antigen presentation.

Role of cytokines in determining T-lymphocyte function

Early events in an immune response stimulate the production of cytokines that direct the subsequent development of T-helper (Th) subsets with discrete patterns of cytokine production. These events are dictated by the type of antigen/microorganism administered to a host, as well as dose and route of immunization. Bacterial stimuli activate macrophages of the innate immune response to produce IL-12 and drive Th1 development and cell-mediated immunity. Conversely, production of IL-4 early in an immune response favors a Th2 or allergic/humoral immune response. The ability of IL-4 and IL-10 to inhibit Th1 development and effector function, as well as the requirement of committed Th1 cells for co-stimulators to induce maximal IFN-gamma production, suggests that cell-mediated immunity is under strict control, probably to achieve immunity with minimum immunopathology.

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.

Flow cytometric determination of cytokines in activated murine T helper lymphocytes: expression of interleukin-10 in interferon-gamma and in interleukin-4-expressing cells

In an immune response, effector functions are controlled by T helper (Th) 1 cytokines [interferon-gamma (IFN-gamma), interleukin (IL)-2 and tumor necrosis factor-beta] and Th2 cytokines (IL-4, IL-5 and IL-10). Here we analyze by multiparameter immunofluorescence to what extent IL-2, IL-4, IL-5, IL-10 and IFN-gamma are co-expressed in individual normal murine Th cells upon activation in vitro with the bacterial superantigen Staphylococcus aureus enterotoxin B, presented in the context of major histocompatibility complex class II. IL-2 and IFN-gamma are co-expressed by some, but not by other Th cells. Expression of IL-4 and IFN-gamma is exclusive. IL-10 is co-expressed in individual cells either with IL-4 or with IFN-gamma. No IL-5-expressing cells are detected. While IL-10- and IL-4-co-expressing Th cells correspond to classical Th 2 cells, cells co-expressing IL-10 and IFN-gamma could be involved in negative-feedback regulation of a Th1 response. Apart from such functional implications, our results show that IL-2, IL-4, IL-5, IL-10 and IFN-gamma are expressed independently of each other in individual murine Th cells.

Induction of interleukin 4 (IL-4) expression in T helper (Th) cells is not dependent on IL-4 from non-Th cells

Interleukin 4 (IL-4) is essential for the induction of immunoglobulin E (IgE) responses in mice. Recent in vitro studies have suggested that IL-4 derived from non T helper (Th) cells, in particular from mast cells and basophils, may be essential for triggering of IL-4 expression in Th cells and may directly contribute to IgE isotype switch induction. Here, we have generated mice carrying a functional IL-4 gene only in Th cells or non-Th cells, respectively, by reconstitution of IL-4-deficient mice (IL-4T mice) with CD4+ or CD4- spleen cells from congenic wild-type animals. In mice in which only CD4+ cells are able to express IL-4, antigen-specific IgE is produced in a T cell-dependent immune response. Thus, induction of IL-4 expression in Th cells can occur in the absence of IL-4 from non-Th cells, which suggests that at least some Th cells can express IL-4 in response to another signal which has yet to be identified. No IgE is detectable, however, in mice in which only CD4- cells can express IL-4, suggesting that Th cells are the primary, if not the only source of IL-4 for initial induction of IgE synthesis.

Induction of hapten-specific tolerance by interleukin 10 in vivo

Interleukin 10 (IL-10) is released during the induction phase of contact sensitivity and was shown in prior functional studies to convert epidermal Langerhans cells (LC) from potent inducers of primary immune responses to specifically tolerizing cells in vitro. To investigate whether IL-10 also subserves the function of a tolerizing agent in vivo ears of BALB/c or C3H mice were injected intradermally with 1-2 micrograms of recombinant mouse (rm)IL-10 8 h before epicutaneous application of 3% trinitrochlorobenzene (TNCB; a contact allergen). As a control, mice were injected with phosphate-buffered saline or IL-10 plus neutralizing amounts of anti-IL-10 mAb. 5 d later, mice were challenged with 1% TNCB on contralateral ears and ear swelling response was measured 24 h later. Whereas control-treated mice showed a normal ear swelling response to epicutaneous challenge (delta mm-2 = 25 +/- 5), ear swelling response of IL-10-treated animals was significantly inhibited (delta mm-2 = 3 +/- 2). Coinjection of IL-10-specific mAb together with rmIL-10 completely abrogated this effect. To differentiate between a state of nonresponsiveness and induction of tolerance by IL-10, mice initially treated with IL-10 and TNCB were resensitized with 3% TNCB in the absence of any treatment after 14 d of rest (group 1). Again mice were challenged 5 d later and ear swelling responses were tested. Whereas control mice treated with allergen alone (group 2) showed a good swelling response (delta mm-2 = 28 +/- 6), IL-10-treated mice (group 1) showed a minimal response towards application of allergen (delta mm-2 = 4 +/- 2). To show that anergy induction by IL-10 was antigen-specific, mice initially treated with IL-10 plus TNCB were exposed to 0.5% dinitrofluorobenzene (DNFB) 14 d later (group 1). After challenge with 0.1% DNFB, IL-10-treated mice showed an ear swelling response (delta mm-2 = 13 +/- 3; group 1) similar to that of control mice only sensitized with DNFB (delta mm-2 = 14 +/- 3; group 3). In an attempt to show the induction of antigen-specific tolerance in these mice in vitro, regional lymph nodes of mice initially treated with TNCB plus IL-10 (group 1) and control-treated mice (groups 2 and 3) were prepared and cultured in the presence of TNBS, dinitrobenzene sulfonate (DNBS), or medium to measure antigen-specific proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential expression of APO-1 on human thymocytes: implications for negative selection?

Negative selection during T cell ontogeny involves selective induction of apoptosis in thymocytes. In peripheral lymphoid cells, apoptosis may be mediated via the APO-1 pathway. Here we report that APO-1 is constitutively expressed on the vast majority of human thymocytes but down-regulated at a mature stage of thymocyte development (TCR(hi)). This stage of development is characterized by CD28hi, CD44hi, CD69hi and up-regulation of Bcl-2 protein. We define a new thymocyte subpopulation that expresses high levels of APO-1 and intermediate levels of T cell receptor alpha/beta (TCR(im)/APO-1hi). The TCR(im)/APO-1hi population contains a large fraction of dead cells, suggesting that the APO-1 pathway may be involved in negative selection of at least a fraction of thymocytes after intrathymic activation.

Differential effects of superantigen-induced "anergy" on priming and effector stages of a T cell-dependent antibody response

The in vitro T cell nonresponsiveness or anergy to restimulation with staphylococcal enterotoxin B (SEB) following the in vivo injection of the superantigen is well characterized. Here we use mice transgenic for a V beta 8.2+ T cell receptor (TcR) (reactive with SEB) to establish a large population of anergic T cells in vivo. As expected, peripheral T cells from the SEB injected transgenic mice failed to proliferate or produce interleukin (IL)-2 following restimulation with the superantigen in vitro. However, in this system superantigen reactivity could be restored by either addition of exogenous IL-2, or stimulation with immobilized anti-TcR antibody. To evaluate the effects of superantigen-induced anergy in vivo, SEB-injected or noninjected control transgenic mice were immunized and boosted with the T cell-dependent antigen tetanus toxin (TT). SEB injection of the V beta 8.2+ transgenic mice 5 days prior to the TT immunization inhibited the anti-TT antibody response as measured over a 100-day period, whereas injection of a superantigen which does not interact with the V beta 8.2% TcR (such as SEA) did not. Furthermore, SEB injection of control nontransgenic mice did not interfere with the induction of a high titer anti-TT antibody response. In contrast to the inhibition seen when SEB was given prior to TT immunization, injection of transgenics with SEB either after the priming TT immunization or after the recall booster injection did not significantly influence the titers of anti-TT antibodies produced. These results demonstrate that the establishment of peripheral T cell anergy to superantigens inhibits the specific antigenic priming of helper T cells in vivo, but does not prevent primed T cells from helping B cells to mount an effective antibody response.

Cytokine-mediated regulation of chronic intestinal helminth infection

Most inbred strains of mouse infected with the intestinal nematode Trichuris muris are resistant to infection expelling the parasite before adult worms establish. However, a few susceptible strains exist that are incapable of worm expulsion and harbor chronic infections of mature adult worms. Analyses of in vitro cytokine production by cells from the draining lymph node (mesenteric lymph node) have indicated that expulsion phenotype is tightly correlated with the selective expansion of helper T cells (Th) of the Th1 or Th2 cell subset within the mesenteric lymph node, resulting in susceptibility and resistance to T. muris, respectively. We have now confirmed and extended our in vitro observations in a series of experiments involving the in vivo manipulation of host cytokine levels. Depletion of interferon (IFN)-gamma in normally susceptible mice resulted in expulsion of the parasite, representing the first evidence for a role for IFN-gamma in the establishment of chronic helminth infection. Blocking interleukin (IL)-4 function in normally resistant animals prevented the generation of a protective immune response allowing adult stages of the parasite to develop. Conversely the administration of IL-4 to a normally susceptible host facilitated expulsion and indeed enabled established adult worms to be expelled when administered late in infection. In all cases assessment of a variety of in vivo parameters indicative of a Th1- or Th2-type response (parasite-specific immunoglobulin (Ig) G2a and the parasite-specific IgG1, total IgE levels and intestinal mastocytosis, respectively) demonstrated that the in vivo modulation of a Th1- or Th2-specific cytokine allowed the reciprocal Th cell subset to expand and become dominant with dramatic consequences for worm expulsion.

T-cell subsets in autoimmunity

Although differential cytokine production has been best characterized in CD4+ T cells, it is becoming clear that CD8+ T cells may also be heterogeneous at the level of cytokine production, and that this determines whether they exhibit inflammatory- or suppressor-type properties. Compelling evidence has accumulated in the past few years that cytokines such as interleukin-4, interleukin-10 and transforming growth factor-beta may serve as regulators of cell-mediated immunopathologies by inhibiting the development or effector function of inflammatory T cells that produce cytokines such as interferon-gamma or lymphotoxin.

Antigen-presenting human T cells and antigen-presenting B cells induce a similar cytokine profile in specific T cell clones

One of the factors that may influence the cytokine secretion profile of a T cell is the antigen-presenting cell (APC). Since activated human T cells have been described to express major histocompatibility complex (MHC) class II molecules as well as costimulatory molecules for T cell activation, like e.g. ICAM-1, LFA-3 and B7, they might play a role as APC and be involved in the regulation of T-Tcell interactions. To define further the role of T cells as APC we tested their capacity to induce proliferation and cytokine production in peptide- or allospecific T cell clones and compared it with conventional APC, like B lymphoblasts (B-LCL) or HTLV-1-transformed T cells, or with non-classical APC, like activated keratinocytes or eosinophils. CD4+, DP-restricted T cell clones specific for a tetanus toxin peptide (amino acids 947-967) and CD4+, DR-restricted allospecific T cell clones produced interleukin (IL)-2, IL-4, tumor necrosis factor-alpha and interferon-gamma (IFN-gamma) after phorbol 12-myristate 13-acetate and ionomycin stimulation and a more restricted cytokine pattern after antigen stimulation. Dose-response curves revealed that the antigen-presenting capacity of activated, MHC class II+, B7+ T cells was comparable to the one of B-LCL. Both APC induced the same cytokine profile in the T cell clones despite a weaker proliferative response with T cells as APC. Suboptimal stimulations resulted in a lower IFN-gamma/IL-4 ratio. Cytokine-treated, MHC class II+ keratinocytes and eosinophils differed in the expression of adhesion molecules and their capacity to restimulate T cell clones. The strongly ICAM-1-positive keratinocytes induced rather high cytokine levels. In contrast, eosinophils, which express only low densities of MHC class II and no or only low levels of adhesion molecules (B7, ICAM-1 and LFA3), provided a reduced signal resulting in a diminished IFN-gamma/IL-4 ratio. We conclude that non-classical APC differ in their capacity to restimulate T cell clones, whereby the intensity of MHC class II and adhesion molecules (B7, ICAM-1) expressed seems to determine the efficacy of this presentation.

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.

Interleukin-10-deficient mice develop chronic enterocolitis

Interleukin-10 (IL-10) affects the growth and differentiation of many hemopoietic cells in vitro; in particular, it is a potent suppressor of macrophage and T cell functions. In IL-10-deficient mice, generated by gene targeting, lymphocyte development and antibody responses are normal, but most animals are growth retarded and anemic and suffer from chronic enterocolitis. Alterations in intestine include extensive mucosal hyperplasia, inflammatory reactions, and aberrant expression of major histocompatibility complex class II molecules on epithelia. In contrast, mutants kept under specific pathogen-free conditions develop only a local inflammation limited to the proximal colon. These results indicate that the bowel inflammation in the mutants originates from uncontrolled immune responses stimulated by enteric antigens and that IL-10 is an essential immunoregulator in the intestinal tract.

Endogenous retroviral superantigen presentation by B cells induces the development of type 1 CD4+ T helper lymphocytes

The endogenous retroviral superantigen, minor lymphocyte stimulating antigen (Mls 1a, encoded by Mtv-7), when presented by highly purified B cells induced the development of a highly polarized population of T helper (Th)1 cells from naive peripheral CD4+ T cells in vitro. Immobilized anti-V beta 6 antibodies similarly generated highly polarized, largely V beta 6+, Th 1 populations in vitro. In the presence of exogenous interleukin-4, both stimuli were capable of generating Th 2, rather than Th 1 populations. Mls 1a presentation by B cells in vivo led to the development of an equally polarized Th 1 population. Using monoclonal antibodies against interferon-gamma and transforming growth factor-beta, it was demonstrated that maximal Th 1 development with either stimulus in vitro was dependent on the endogenous production of these two cytokines. Thus, our results demonstrate that the retroviral encoded superantigen, Mls 1a, drives the development of Th 1 cells both in vitro and in vivo, and they suggest that B cell presentation does not, in itself, lead to the generation of Th 2 cells.

Role of transforming growth factor-beta in the preferential induction of T helper cells of type 1 by staphylococcal enterotoxin B

Stimulation of murine CD4+ T cells with staphylococcal enterotoxin B (SEB) results in the preferential development of T helper (Th) 1 cells [i.e. high interferon (IFN)-gamma and low interleukin (IL)-4, IL-5 and IL-10]; whereas in response to plate-bound anti-CD3 or anti-T cell receptor-alpha beta, Th1 as well as Th2 cells develop. In the present study, we examined the mechanism which is responsible for the selective Th1 development in the SEB system. The addition of IL-4 resulted in a strong development of Th2 cells showing that SEB stimulation can result in Th2 differentiation. Co-stimulation with anti-CD28 was insufficient in this regard. Lack of Th2 development in the SEB system was in part due to the inhibitory effect of endogenously produced transforming growth factor-beta (TGF-beta), because anti-TGF-beta allowed the development of Th2 cells. Similarly, TGF-beta inhibited Th2 development and stimulated Th1 development in the anti-CD3 system. This shift was only partially prevented by also including IL-4 in the cultures. The effects of TGF-beta could only partially be explained by stimulation of IFN-gamma or inhibition of IL-4 as intermediatory cytokines: (1) TGF-beta stimulated Th1 development even in the presence of anti-IL-4 and anti-IFN-gamma, and (2) a strong inhibitory effect of anti-TGF-beta on Th1 development was still observed when anti-IL-4 and IFN-gamma were simultaneously added to the cultures. It is concluded that SEB favors Th1 development by stimulation of TGF-beta production. Inhibition of Th2 development by TGF-beta is due, in part, to inhibition of IL-4 and stimulation of IFN-gamma, and, in part, to a direct effect of TGF-beta on the responding T cells.

Epidermal Langerhans cells are critical for immunoregulation of cutaneous leishmaniasis

In leishmaniasis, macrophages are known to play a central role as modulators of the specific immune activity. In this article, Heidrun Moll presents evidence for the critical involvement of another component of the skin immune system, the epidermal Langerhans cell. She proposes that Langerhans cells take up parasites in the skin and transport them to the draining lymph node for presentation to T cells and initiation of the specific immune response.