Localization dose and time of antigens determine immune reactivity

Rheumatoid arthritis

Therapeutic efficacy of depleting B cells or blocking T-cell costimulation in rheumatoid arthritis (RA) has confirmed the critical pathogenic role of adaptive immune responses. Yet, RA preferentially affects elderly individuals, in whom adaptive immunity to exogenous antigens begins to fail. Here, we propose that senescence of the immune system is a risk factor for RA, with chronic inflammation resulting from the accumulation of degenerate T cells that have a low threshold for activation and utilize a spectrum of novel receptors to respond to microenvironmental cues. The process of immunosenescence is accelerated in RA and precedes the onset of disease, the acceleration, in part, being conferred by the HLA-DR4 haplotype. Naive CD4(+) T cells in RA are contracted in diversity and restricted in clonal burst. Senescence of effector CD4(+) T cells is associated with the loss of CD28 and the de novo expression of KIR2DS2, NKG2D, and CX(3)CR1, all of which function as costimulatory molecules and reduce the threshold for T-cell activation. The synovial microenvironment promotes chronic persistent immune responses by facilitating ectopic lymphoid neogenesis, such as the formation of aberrant germinal centers. With the propensity to develop complex lymphoid architectures and to provide optimal activation conditions for senescent CD4(+) T cells, the synovium becomes a natural target for pathogenic immune responses in prematurely aged individuals.

Tumor necrosis factor family members and inflammatory bowel disease

Tumor necrosis factor (TNF) is one of the most potent effector cytokines in the pathogenesis of inflammatory bowel disease (IBD). Previous studies strongly implicate the critical involvement of several TNF family members in human IBD. This review focuses on the recent studies of TNF family members in IBD development. In particular, we discuss the findings about LIGHT (homologous to lymphotoxins, inducible expression, competes with herpes simplex virus glycoprotein D for herpes viral entry mediator, a receptor expressed on T lymphocytes) in the pathogenesis of IBD, and the potential mechanisms by which LIGHT induces IBD. Such mechanisms may also apply to other TNF family members.

Dendritic-cell-based therapeutic vaccination against cancer

Early clinical trials, in which over 1000 cancer patients received dendritic cell (DC) vaccines, tested different vaccine preparations, but they did not always induce sufficient acquired immunity or meet the expected level of tumor regressions. Current studies aim to improve the DC vaccine approach and capture the potential of these cells in order to gain access to lymphoid tissues and induce strong cell-mediated immunity. DC clinical trials are moving towards a more professional environment, in accordance with the latest quality standards. This explains the current need for innovative well designed trials with defined endpoints that induce robust anti-tumor immunity.

Primary hemophagocytic syndromes point to a direct link between lymphocyte cytotoxicity and homeostasis

Hemophagocytic syndrome (HS) is a severe and often fatal syndrome resulting from potent and uncontrolled activation and proliferation of T-lymphocytes, leading to excessive macrophage activation and multiple deleterious effects. The onset of HS characterizes several inherited disorders in humans. In each condition, the molecular defect impairs the granule-dependent cytotoxic activity of lymphocytes, thus highlighting the determinant role of this function in driving the immune system to a state of equilibrium following infection. It has also been shown that some of the proteins required for lytic granule secretion are required for melanocyte function, leading to associated hypopigmentation in these conditions. This review focuses on several effectors of this secretory pathway, recently identified, because their defects cause these disorders, and discusses their role and molecular interactions in granule-dependent cytotoxic activity.

Immunization with cytoplasmic repetitive antigen and flagellar repetitive antigen of Trypanosoma cruzi stimulates a cellular immune response in mice

In previous studies, we demonstrated that CRA and FRA recombinant proteins, used for diagnosis of Chagas' disease, elicited a humoral immune response in susceptible and resistant mice. To understand better the immune response to these proteins, we have evaluated, the cellular immune response in CRA- and in FRA-immunized BALB/c and C57BL/6 mice. A specific cellular lymphoproliferative response was observed in both strains of mice. Spleen cell cultures mainly from CRA-immunized C57BL/6 and FRA-immunized BALB/c mice produced high levels of IFN-y, indicating the induction of a Type 1 immune response. Regarding the T cell subsets, CD4+ T cells were the major source of IFN-y in CRA- and FRA-immunized mice. These results suggest that CRA and FRA are important immunogens in inducing a Type 1 immune response and that they may be considered as potential vaccine antigens.

Humoral and cellular immune responses in BALB/c and C57BL/6 mice immunized with cytoplasmic (CRA) and flagellar (FRA) recombinant repetitive antigens, in acute experimental Trypanosoma cruzi infection

In previous studies, cytoplasmic repetitive antigen (CRA) and flagellar repetitive antigen (FRA) proteins induced specific humoral and cellular immune responses in susceptible and resistant mice in the absence of Trypanosoma cruzi infection with a significant induction of the Interferon-gamma (IFN-gamma) production in those animals. In this follow-up paper, the immunostimulatory and protective effects of these proteins were evaluated by immunizing with CRA or FRA antigens, BALB/c and C57BL/6 mice and challenging with a T. cruzi (Y strain). Both proteins induced humoral response with high levels of IgG isotypes as well as cellular immunity with high levels of IFN-gamma when compared to controls. However, the lymphocyte proliferative response was minimal. The survival rate at 30 days post-infection was significant in CRA (60%) or FRA (50%)--immunized BALB/c mice and CRA (83.3%)--immunized C57BL/6 mice. Taken as a whole these findings indicate that CRA and FRA are immunogenic and potentially important for protective immunity.

Peripheral Tolerance of CD8 T Lymphocytes

Whereas high-avidity recognition of peptide-MHC complexes by developing T cells in the thymus results in deletion and promotes self-tolerance, such recognition by mature T cells in the periphery results in activation and clonal expansion. This dichotomy represents the basis of a dilemma that has stumped immunologists for many years, how are self-specific T cells tolerized in the periphery? There appear to be two important criteria used to achieve this goal. The first is that in the absence of inflammatory pathogens, tolerance is promoted when T cells recognize antigen presented by quiescent dendritic cells (DCs) expressing low levels of costimulatory molecules. A second critical factor that defines "self" and drives tolerance through deletion, anergy, or suppression is the persistence of antigen.

Ambient air particles from four European cities increase the primary cellular response to allergen in the draining lymph node

In the RAIAP (respiratory allergy and inflammation due to ambient particles) project, qualitative properties of ambient air particles from Amsterdam, Oslo, Lodz and Rome were investigated in relation to inflammation and allergy. Most collected particle fractions were found to increase the allergen-specific IgE and IgG2a responses after subcutaneous injection of particles with allergen in mice. However, some fractions appeared to skew the antibody response towards more Th1- or Th2-associated antibody isotypes, and the fine fractions were found to be more potent than the coarse fractions with regard to IgE adjuvant activity. In the present study we investigated the cellular response in the draining lymph node 5 days after a subcutaneous injection of selected RAIAP particle fractions. The particles (100 microg) were injected into both hind footpads of BALB/cA mice, in the presence or absence of the allergen ovalbumin (OVA, 50 microg). We also studied if the coarse and fine RAIAP particle fractions affected the cellular responses to OVA differently. The number of lymph node cells, as well as the relative number of B and T lymphocytes and T helper cells were determined. Expression of cell surface molecules (MHC class II, CD86 and CD23) and ex vivo cytokine production (IL-4, IL-10 and IFN-gamma) by the lymph node cells were measured. Overall, particles in the presence of allergen enhanced the levels of the various cellular parameters compared to allergen alone or particles alone. In the absence of allergen, ambient air particles, in contrast to diesel exhaust particles, marginally affected some cellular parameters. By histological examination of the lymph node, the particles appeared to be scattered between the lymphocytes, often localised within macrophage-like (acid phosphatase positive) cells. The cell parameters measured could, for the individual sample, neither predict the degree of a Th2- or Th1-skewed antibody response, nor the stronger antibody adjuvant capacity of the fine than the coarse particle fractions. In conclusion, we have shown that coarse and fine ambient air particles from different European cities enhance the cellular response in the draining lymph node after injection with an allergen. In the absence of allergen, ambient particles only marginally affected the cellular parameters.

LJP 1082: a toleragen for Hughes syndrome

A hallmark of systemic lupus erythematosus (SLE) and related autoimmune diseases such as the antiphospholipid syndrome (APL or Hughes syndrome) is an apparent breakdown in tolerance, the process by which the body distinguishes self from nonself in order to maintain a versatile immune defense while protecting itself from self-annihilation. To some extent, loss of tolerance is a desirable feature of host immunity, and is known to occur in healthy individuals. Optimal tolerance then is probably not an all or nothing phenomenon. Autoimmunity should be seen as a breakdown in homeostasis rather than a completely aberrant kind of immunity. This leads to special considerations in the assessment of potentially toleragenic therapies, in which an attempt is made to re-educate the immune system. LJP 1082 is designed as a polyvalent antigenic structure aimed at crosslinking specific surface immunoglobulin and tolerizing B cells to beta2-glycoprotein I. Issues of antigenic selection and multiplex forces influencing tolerance and immunity may have impact on its optimal development and use in patients.

Identification of Monoclonal Anti-HMW-MAA Antibody Linear Peptide Epitope by Proteomic Database Mining

An efficient strategy is presented for the identification of antigenic sequences in the context of given MHC molecules of interest. The proteomic analysis of the antigenic peptide repertoire is described and demonstrated by using high-molecular weight melanoma-associated antigen. The identification of the epitopic sequence of a monoclonal antibody raised against the 250 kDa tumor associated antigen was reached by using only seven short synthetic peptide fragments, instead of the 155 non-overlapping 15-mer peptides theoretically necessary as minimum screening library. The present result has been obtained by applying as driving criteria the analysis of the peptide affinity to MHC class II molecules and the non-self discrimination concept.

The road to tolerance: renal transplant tolerance induction in nonhuman primate studies and clinical trials

Organ transplantation has become a standard life-saving therapy for many causes of end stage organ failure. Although valuable, it remains hampered by the requirement for, and complications of, immunosuppression to prevent immune rejection of the transplanted organ. It is now clear that rejection can be avoided in some experimental systems without a requirement of immunosuppressive medication, and these experimental concepts are now making their way into the clinic in the form of early transplantation tolerance trials. This manuscript will discuss the most promising techniques for tolerance induction, namely, costimulation blockade, lymphocyte depletion, and mixed chimerism. Seminal preclinical studies will be cited and the results of initial clinical trials will be reviewed. The data to date indicate that while tolerance remains elusive, immunosuppression minimization is a feasible near-term alternative.

Targeting of secretory IgA to Peyer's patch dendritic and T cells after transport by intestinal M cells

In addition to being instrumental to the protection of mucosal epithelia, secretory IgA (SIgA) adheres to and is transported by intestinal Peyer's patch (PP) M cells. The possible functional reason for this transport is unknown. We have thus examined in mice the outcome of SIgA delivered from the intestinal lumen to the cells present in the underlying organized mucosa-associated lymphoreticular tissue. We show selective association of SIgA with dendritic cells and CD4(+) T and B lymphocytes recovered from PP in vitro. In vivo, exogenously delivered SIgA is able to enter into multiple PP lining the intestine. In PP, SIgA associates with and is internalized by dendritic cells in the subepithelial dome region, whereas the interaction with CD4(+) T cells is limited to surface binding. Interaction between cells and SIgA is mediated by the IgA moiety and occurs for polymeric and monomeric molecular forms. Thus, although immune exclusion represents the main function of SIgA, transport of the Ab by M cells might promote Ag sampling under neutralizing conditions essential to the homeostasis of mucosal surfaces.

The dominant-negative herpes simplex virus type 1 (HSV-1) recombinant CJ83193 can serve as an effective vaccine against wild-type HSV-1 infection in mice

By selectively regulating the expression of the trans-dominant-negative mutant polypeptide UL9-C535C, of herpes simplex virus type 1 (HSV-1) origin binding protein UL9 with the tetracycline repressor (tetR)-mediated gene switch, we recently generated a novel replication-defective and anti-HSV-specific HSV-1 recombinant, CJ83193. The UL9-C535C peptides expressed by CJ83193 can function as a potent intracellular therapy against its own replication, as well as the replication of wild-type HSV-1 and HSV-2 in coinfected cells. In this report, we demonstrate that CJ83193 cannot initiate acute productive infection in corneas of infected mice nor can it reactivate from trigeminal ganglia of mice latently infected by CJ83193 in a mouse ocular model. Given that CJ83193 is capable of expressing the viral alpha, beta, and gamma1 genes but little or no gamma2 genes, we tested the vaccine potential of CJ83193 against HSV-1 infection in a mouse ocular model. Our studies showed that immunization with CJ83193 significantly reduced the yields of challenge HSV in the eyes and trigeminal ganglia on days 3, 5, and 7 postchallenge. Like in mice immunized with the wild-type HSV-1 strain KOS, immunization of mice with CJ83193 prevents the development of keratitis and encephalitis induced by corneal challenge with wild-type HSV-1 strain mP. Delayed-type hypersensitivity (DTH) assays demonstrate that CJ83193 can elicit durable cell-mediated immunity at the same level as that of wild-type HSV-1 and is more effective than that induced by d27, an HSV-1 ICP27 deletion mutant. Moreover, mice immunized with CJ83193 developed strong, durable HSV-1-neutralizing antibodies at levels at least twofold higher than those induced by d27. The results presented in this report have shed new light on the development of effective HSV viral vaccines that encode a unique safety mechanism capable of inhibiting the mutant's own replication and that of wild-type virus.

Underwhelming the immune response: effect of slow virus growth on CD8+-T-lymphocyte responses

The speed of virus replication has typically been seen as an advantage for a virus in overcoming the ability of the immune system to control its population growth. Under some circumstances, the converse may also be true: more slowly replicating viruses may evoke weaker cellular immune responses and therefore enhance their likelihood of persistence. Using the model of lymphocytic choriomeningitis virus (LCMV) infection in mice, we provide evidence that slowly replicating strains induce weaker cytotoxic-T-lymphocyte (CTL) responses than a more rapidly replicating strain. Conceptually, we show a "bell-shaped" relationship between the LCMV growth rate and the peak CTL response. Quantitative analysis of human hepatitis C virus infections suggests that a reduction in virus growth rate between patients during the incubation period is associated with a spectrum of disease outcomes, from fulminant hepatitis at the highest rate of viral replication through acute resolving to chronic persistence at the lowest rate. A mathematical model for virus-CTL population dynamics (analogous to predator [CTL]-prey [virus] interactions) is applied in the clinical data-driven analysis of acute hepatitis B virus infection. The speed of viral replication, through its stimulus of host CTL responses, represents an important factor influencing the pathogenesis and duration of virus persistence within the human host. Viruses with lower growth rates may persist in the host because they "sneak through" immune surveillance.

Beyond the red cell: pegylation of other blood cells and tissues

Immunological recognition of allogeneic tissue is of critical concern in transfusion and transplantation medicine. While the major emphasis of our work on the immunocamouflage of cells has been focused on the erythrocyte, we have extended this research beyond the red blood cell (RBC) to other tissues. Our studies from blood transfusion (i.e., a specialized form of cellular transplantation) suggest that covalent modification of cells and tissues with methoxypoly(ethylene glycol) mPEG can significantly diminish immunologic recognition of other allogeneic tissues and, furthermore, may enhance the induction of tolerance. The mechanisms underlying the mPEG-mediated immunocamouflage of alloantigens is the global camouflaging of antigenic sites, membrane surface charge and the attenuation of receptor-ligand and cell-cell interactions. As a consequence of the immunocamouflage imparted by the grafted mPEG, weak costimulation of alloreactive T cells is observed which subsequently induces apoptosis of these reactive cells. As a result of this clonal deletion, a pro-tolerance state is induced. The potency of immunocamouflage is readily observed in in vivo murine models of transfusion-associated graft versus host disease. Furthermore, initial studies on the in vivo transplantation of pegylated rat and murine pancreatic islets have demonstrated that mPEG-derivatization does not impair the finely tuned signaling necessary for glucose homeostasis. Finally, in contrast to the pharmacological inhibition of the immune response by agents such as cyclosporine, mPEG-mediated immunocamouflage directly attenuates the inherent antigenicity and immunogenicity of the donor tissue itself while leaving the recipient a fully competent immune system.

Exploiting natural immunity to helminth parasites for the development of veterinary vaccines

The development of subunit vaccines against most parasitic helminth infections will require a better understanding of the different components of a natural rejection process including (1) recognition of parasite antigens; (2) induction of protective immune response phenotypes; and (3) activation of appropriate immune effector mechanisms. While novel technologies have allowed significant progress to be made in the identification of candidate vaccine antigens, the large scale production of these antigens and their presentation to the host with appropriate adjuvant systems remains a major problem in vaccine research. Identification of the molecular interactions involved in the innate immune response to helminth infections and the application of new genomic and proteomic technologies are likely to lead to major advances in these research fields. Gastrointestinal nematode parasites and liver fluke are the most important helminth parasites of production animals. In recent years, a lot of new knowledge has been gathered on the immunobiology of the host-parasite interactions in these two infection systems, which has allowed new vaccination strategies to be considered. Functional genomic technologies such as gene expression analysis by microarrays, promise to further advance our understanding of the molecular pathways leading to protection against parasite infections. This will not only have implications for vaccine research, but also provide novel targets for drug development and genetic selection.

Drug hypersensitivity reactions in skin: understanding mechanisms and the development of diagnostic and predictive tests

Cutaneous manifestations of drug hypersensitivity can be serious and potentially life threatening and may prevent effective drug therapy. T cells play an important role in the pathology of drug hypersensitivity reactions. Classical studies suggest that T-cell activation requires drug bioactivation, covalent binding to protein and antigen processing to stimulate an immune response. Recent studies have shown that drugs can also be presented to T cells in the absence of antigen processing and drug metabolism. In this article, sulfamethoxazole is used as a paradigm to describe the chemical mechanisms involved in the initiation and maintenance of an aberrant drug antigen specific T-cell response. Presentation of the same drug to different individuals can cause a variety of skin diseases. Such reactions have been classified according to the phenotype and functionality of the T-cell response. This review summarises the different forms of cutaneous hypersensitivity reactions and describes how T-cell clones generated from hypersensitive patients have been used to study the cellular mechanisms of anticonvulsant hypersensitivity. Potential uses of in vitro cell culture assays for patient diagnosis and drug evaluation are also discussed.

Safety and efficacy of factor IX gene transfer to skeletal muscle in murine and canine hemophilia B models by adeno-associated viral vector serotype 1

Adeno-associated viral (AAV) vectors (serotype 2) efficiently transduce skeletal muscle, and have been used as gene delivery vehicles for hemophilia B and for muscular dystrophies in experimental animals and humans. Recent reports suggest that AAV vectors based on serotypes 1, 5, and 7 transduce murine skeletal muscle much more efficiently than AAV-2, with reported increases in expression ranging from 2-fold to 1000-fold. We sought to determine whether this increased efficacy could be observed in species other than mice. In immunodeficient mice we saw 10- to 20-fold higher levels of human factor IX (hF.IX) expression at a range of doses, and in hemophilic dogs we observed approximately 50-fold higher levels of expression. The increase in transgene expression was due partly to higher gene copy number and a larger number of cells transduced at each injection site. In all immunocompetent animals injected with AAV-1, inhibitory antibodies to F.IX developed, but in immunocompetent mice treated with high doses of vector, inhibitory antibodies eventually disappeared. These studies emphasize that the increased efficacy of AAV-1 vectors carries a risk of inhibitor formation, and that further studies will be required to define doses and treatment regimens that result in tolerance rather than immunity to F.IX.

Mucosal immunity: overcoming the barrier for induction of proximal responses

Vaccination represents one of the most efficacious and cost-effective medical interventions. It is the only medical intervention proven to eliminate disease at a global level. Many of the pathogens against which we most require adequate vaccines infect via the highly exposed mucosal surfaces. For this reason the mucosa is often considered the first, and sometimes only, line of defense. Therefore, responses that protect the local mucosa are vital. In this review, we first explore the immunological mechanisms that protect the mucosa. We then review the literature of mucosal vaccines within the principles of antigenic composition, dose, and danger, highlighting the need and niche for the next generation of mucosal vaccines.

Generation of antibodies to the urokinase receptor (uPAR) by DNA immunization of uPAR knockout mice: membrane-bound uPAR is not required for an antibody response

The urokinase receptor (uPAR) is a glycolipid-anchored cell surface glycoprotein that plays a central role in extracellular proteolysis during tissue remodeling processes including cancer invasion. Furthermore, uPAR is found on the surface of both dendritic cells (DCs) and T cells, and has been proposed to play a role in DC-induced T-cell activation and, therefore, in the induction of an immune response. In order to investigate the possibility of using DNA immunization for the generation of poly- and monoclonal antibodies to uPAR, we injected wild-type mice and mice deficient in uPAR (uPAR knockouts) intramuscularly with plasmid DNA encoding a carboxy-terminal truncated soluble form of the human uPAR. Multiple injections of 100 micro g of DNA resulted in a strong and specific antibody response in all mice irrespective of genotype. Antisera with a maximum titre of 32,000 were obtained, comparable with that obtained after immunization with recombinant uPAR. The subclass distribution of uPAR-specific antibodies in the sera demonstrated the induction of a mixed TH1/TH2 response, irrespective of the genotype of the mice. Our results demonstrate the possibility of generating high titre antibodies to uPAR by DNA immunization of wild-type as well as uPAR knockout mice, and that cell surface uPAR is not indispensable for the generation of a humoral immune response.

On natural and artificial vaccinations

This review summarizes the general parameters of cell- and antibody-mediated immune protection and the basic mechanisms responsible for what we call immunological memory. From this basis, the various successes and difficulties of vaccines are evaluated with respect to the role of antigen in maintaining protective immunity. Based on the fact that in humans during the first 12-48 months maternal antibodies from milk and serum protect against classical acute childhood and other infections, the concept is developed that maternal antibodies attenuate most infections of babies and infants and turn them into effective vaccines. If this "natural vaccination" under passive protective conditions does not occur, acute childhood diseases may be severe, unless infants are actively vaccinated with conventional vaccines early enough, i.e., in synchronization with the immune system's maturation. Although vaccines are available against the classical childhood diseases, they are not available for many seemingly milder childhood infections such as gastrointestinal and respiratory infections; these may eventually trigger immunopathological diseases. These changing balances between humans and infections caused by changes in nursing habits but also in hygiene levels may well be involved in changing disease patterns including increased frequencies of certain autoimmune and degenerative diseases.

Measles virus and dendritic cell functions: how specific response cohabits with immunosuppression

Measles virus (MV) infection induces both an efficient MV-specific immune response and a transient but profound immunosuppression characterised by a panlymphopenia that occasionally results in opportunistic infections responsible for a high rate of mortality in children. On the basis of in vitro studies, the putative roles of dendritic cells (DCs) in MV infection are discussed. (1) DCs could participate in anti-MV innate immunity because MV turns on TNF-related apoptosis-inducing ligand (TRAIL)-mediated DC cytotoxicity. (2) Cross-priming by non-infected DCs might be the route of MV adaptive immune response. (3) After CD40-ligand activation in secondary lymphoid organs, MV-infected DCs could initiate the formation of Warthin-Finkeldey multinucleated giant cells, replicating MV and responsible for in vivo spreading of MV. (4) We review how integrated viral attack of the host immune system also targets DCs: Progress in understanding the immunobiology of MV-infected DCs that could account for MV-induced immunosuppression observed in vivo is presented and their potential role in lymphopenia is underlined. In conclusion, future research directions are proposed.

The power of the third dimension: tissue architecture and autoimmunity in rheumatoid arthritis

Lymphoid organs are the anatomic solution to the challenge of responding to minute amounts of antigen with powerful effector mechanisms. By arranging interacting cells in complex three-dimensional topographies lymphoid organs provide an optimal match between form and function. This principle is exploited in ectopic lymphoid structures that characteristically appear in rheumatoid synovitis. Synovial tissue T cells and B cells cooperate in different types of lymphoid organizations. Dendritic cell networks in the inflamed synovial membrane optimize antigen collection, storage, processing, and presentation. Synovial tissue cells participate in lymphocyte recruitment and the formation of tissue architectures that amplify immune responses. Recent data support the concept that the tissue organization in the rheumatoid joint fosters a breakdown in self-tolerance by promoting a phase transition from self-limited immune responses to self-perpetuating autoimmune responses.

Humoral immune response in mice against a circulating antigen induced by adenoviral transfer is strictly dependent on expression in antigen-presenting cells

Adenoviral transfer of human apo A-I in Balb/c mice induces a strong humoral immune response against the transgene product when expression is driven from the ubiquitously active CMV promoter but induces no immune response when driven by the hepatocyte-specific 256-base pair apo A-I promoter. Here the hypothesis was tested, which is that the humoral immune response against the circulating transgene product correlates with its expression in antigen-presenting cells. No humoral immune response was observed after adenoviral transfer of vectors with human apo A-I expression driven by the hepatocyte-specific apo C-II or 1.5-kilobase (kb) human alpha(1)-antitrypsin promoter, but antibodies were induced after transfer with vectors driven by the ubiquitously active U1b promoter and the murine MHCII E beta promoter. A strict correlation was observed between antigen expression in the spleen and the occurrence of an immune response. Coinjection of the 1.5-kb human alpha(1)-antitrypsin and the murine MHCII E beta promoter-driven vectors resulted in a very short-lived humoral immune response against human apo A-I, suggesting that the time course of human apo A-I expression is a critical determinant of the development of tolerance for human apo A-I. High titers of antibodies against human apo A-I after subcutaneous gene transfer with the MHCII E beta promoter-driven vector underscore the potential of this promoter for vaccination purposes. In conclusion, humoral immune response in mice against a circulating antigen induced by adenoviral transfer is strictly dependent on expression in antigen-presenting cells.

Vaccine adjuvant technology: from mechanistic concepts to practical applications

Distinct types of immune responses are required for efficient elimination of different pathogens. Programming of the desired type of immune response by safe nonreplicating vaccines requires suitable vaccine adjuvants. Adjuvants largely determine the magnitude and quality of immune responses specific for the coadministered antigen. Unfortunately, rational vaccine design requiring a rational choice of vaccine adjuvant, is hampered by a lack of knowledge about the mechanism(s) of vaccine adjuvant activity. The current review addresses different critical immunological processes possibly explaining adjuvant functions. In addition, we discuss traditional vaccine adjuvant formulations and their possible mode of action. Finally, we reflect on the latest technologies for the identification of novel adjuvants using molecular analysis of immune activation and functional genomics.

Ectopic germinal center formation in rheumatoid synovitis

Synovial inflammation in rheumatoid arthritis is closely related to the formation of ectopic lymphoid microstructures. In synovial tissue from some patients, one finds seemingly diffuse infiltrates; in others, T cells and B cells cluster in aggregates with interdigitating dendritic cells (DCs) but no follicular DCs (FDCs). In a third group, T cell/B cell follicles with germinal center (GC) reactions are generated. Within a given patient, aggregates and GCs are mutually exclusive and stable over time. Because antigen storage capacity, lymphoid density, and three-dimensional topography of GCs optimize immune responses, synovial GCs should play a crucial role in the breakdown of self-tolerance. We have identified factors critical for ectopic GCs, thereby transforming the synovial inflammatory process. Tissues with GCs produced 10- to 20-fold higher amounts of the chemokines CXCL13 and CCL21. CXCL13 derived from three sources, endothelial cells, synovial fibroblasts, and FDC networks. The level of CXCL13 transcripts strongly predicted GCs; however, some tissues had high levels of CXCL13 but lacked GCs. Tissue expression of LT-beta emerged as a second key factor. LT-beta protein was detected on follicular center and mantle zone B cells. Multivariate regression analysis identified CXCL13 and LT-beta as the only cytokines predicting GCs. Remarkably, LT-alpha did not contribute independently. The contribution of B cells to ectopic lymphoid organogenesis was not limited to LT-beta production. Rather, synovial tissue B cells were critical in regulating T cell activation. In adoptive transfer experiments in human synovium-SCID mouse chimeras, activation of synovium-derived CD4 T cells was strictly dependent on T cell/B cell follicles. Depletion of synovial tissue B cells abrogated T cell function, and non-B cell antigen-presenting cells could not maintain T cell stimulation. Unexpectedly, GC function in the rheumatoid lesion was also dependent on CD8 T cells. The majority of T cell receptors derived from CD8 T cells were shared between distinct GCs. Depletion of CD8 T cells disrupted synovial GCs, FDC networks disappeared, and transcription of LT-beta, IgG, and Igkappa declined. Follicle-sustaining CD8 T cells were located at the edge of or within the mantle zone. Cell-cell communication in the mantle zone, including CD8 T cells, appears to be critical for ectopic GC formation in rheumatoid synovitis.

Antigen-induced regulatory T cells in autoimmunity

The ultimate goal of any treatment for autoimmune diseases is antigen- and/or site-specific suppression of pathology. Autoaggressive lymphocytes need to be eliminated or controlled to prevent tissue damage and halt the progression of clinical disease. Strong evidence is emerging that the induction of regulatory T (T(Reg)) cells by autoantigens can suppress disease, even if the primary, initiating autoantigens are unknown and if inflammation is progressive. An advantage of these autoreactive T(Reg) cells is their ability to act as bystander suppressors and dampen inflammation in a site-specific manner in response to cognate antigen expressed locally by affected tissues. In this review, we consider the nature and function of such antigen-specific T(Reg) cells, and strategies for their therapeutic induction are discussed.

Increasing tumor antigen expression overcomes "ignorance" to solid tumors via crosspresentation by bone marrow-derived stromal cells

To explain why solid cancers grow or are rejected, we examined how the tumor stroma affected the level of antigen expression necessary to induce an immune response. We applied a tamoxifen-regulated Cre-loxP system to induce a model SIYRYYGL antigen recognized by the 2C T cell receptor. Solid tumors expressing the antigen at lower levels grew, whereas solid tumors expressing antigen induced to 26-fold higher levels were rejected. In contrast, mice rejected cell suspensions expressing higher or lower levels of the antigen. The antigen was likely crosspresented because draining lymph node responses required bone marrow-derived cells in the tumor stroma. Thus, tumor antigens expressed at levels sufficient for crosspresentation by bone marrow-derived stromal cells may overcome immunological "ignorance" to solid tumors.

Dangerous liaisons: the role of "danger" signals in the immune response to gene therapy

Recent studies in gene transfer suggest that the innate immune system plays a significant role in impeding gene therapy. In this review, we examine factors that might influence the recruitment and activation of the innate system in the context of gene therapy. We have adopted a novel model of immunology that contends that the immune system distinguishes not between self and nonself, but between what is dangerous and what is not dangerous. In taking this perspective, we provide an alternative and complementary insight into some of the failures and successes of current gene therapy protocols.

Humoral immune response to recombinant adenovirus and adeno-associated virus after in utero administration of viral vectors in mice

Adenovirus and adeno-associated virus vector-mediated gene delivery is limited by the induction of a humoral immune response that prevents readministration. To determine whether viral delivery in the "preimmune" fetus would produce dose- or time-dependent tolerance, we evaluated the humoral immune response after sequential pre- and postnatal virus administration. We evaluated six injection route and viral dose combinations of adenovirus (intra-amniotic, intrahepatic, and intramuscular injection at 4 x 10(8) and 2 x 10(9) particles/fetus) at d 15 postconception (p.c.); three route and dose combinations at d 13 p.c. (intramuscular injection at 1 x 10(8), 3 x 10(8), and 5 x 10(8) particles/fetus); and one route and dose combination of adeno-associated virus (intramuscular at 2.5 x 10(10) genome copies/fetus) at d 15 p.c. In utero injection of either viral vector at any route and dose combination resulted in the production of low titers of neutralizing antivirus and antitransgene (beta-galactosidase) antibodies. This primary immune response only partially blocked transgene expression after the readministration of viral vectors postnatally. However, delivery of the virus postnatally triggered an immune response that completely blocked transgene expression after a third viral injection. Together, these results suggest that, for B6/129 F1 mice, in utero injection of recombinant adenovirus or adeno-associated virus between d 13 and 15 p.c. does not induce tolerance to the viral vector or transgene product.

Functional heterogeneity of vaccine-induced CD8(+) T cells

The functional status of circulating vaccine-induced, tumor-specific T cells has been questioned to explain their paradoxical inability to inhibit tumor growth. We enumerated with HLA-A*0201/peptide tetramers (tHLA) vaccine-elicited CD8(+) T cell precursor frequency among PBMC in 13 patients with melanoma undergoing vaccination with the HLA-A*0201-associated gp100:209-217(210 M) epitope. T cell precursor frequency increased from undetectable to 12,400 +/- 3,600 x 10(6) CD8(+) T cells after vaccination and appeared heterogeneous according to previously described functional subtypes: CD45RA(+)CD27(+) (14 +/- 2.6% of tHLA-staining T cells), naive; CD45RA(-)CD27(+) (14 +/- 3.2%), memory; CD45RA(+)CD27(-) (43 +/- 6%), effector; and CD45RA(-)CD27(-) (30 +/- 4.1%), memory/effector. The majority of tHLA(+)CD8(+) T cells displayed an effector, CD27(-) phenotype (73%). However, few expressed perforin (17%). Epitope-specific in vitro stimulation (IVS) followed by 10-day expansion in IL-2 reversed this phenotype by increasing the number of perforin(+) (84 +/- 3.6%; by paired t test, p < 0.001) and CD27(+) (from 28 to 67%; by paired t test, p = 0.01) tHLA(+) T cells. This conversion probably represented a change in the functional status of tHLA(+) T cells rather than a preferential expansion of a CD27(+) (naive and/or memory) PBMC, because it was reproduced after IVS of a T cell clone bearing a classic effector phenotype (CD45RA(+)CD27(-)). These findings suggest that circulating vaccine-elicited T cells are not as functionally active as inferred by characterization of IVS-induced CTL. In addition, CD45RA/CD27 expression may be more informative about the status of activation of circulating T cells than their status of differentiation.

CD40 ligation in the presence of self-reactive CD8 T cells leads to severe immunopathology

Previous work has shown that stimulation of APCs via CD40 strongly influences the outcome of a CD8 T cell response. In this study, we examined the effect of CD40 ligation on peripheral tolerance induction of self-reactive CD8 T cells in an adoptive transfer model. Naive CD8 T cells from TCR-transgenic (tg) mice specific for the gp33 epitope of lymphocytic choriomeningitis virus were tolerized when transferred into H8-tg mice expressing the gp33 epitope under the control of a MHC class I promoter. However, if the H8 recipient mice were treated with agonistic anti-CD40 Abs, TCR-tg cells vigorously proliferated, and induced destruction of lymphoid organs and hepatitis. Break of peripheral tolerance induction was B cell independent and did not require CD28/B7 interactions. These findings provide further in vivo evidence for the crucial role of the activation state of the APC in peripheral tolerance induction and suggest the need for caution in systemically activating APC via CD40 ligation in the presence of self-reactive T cells.

Peptide mimotopes as surrogate antigens of carbohydrates in vaccine discovery

Carbohydrate antigens are immune targets associated with a variety of pathogens and tumor cells. Unfortunately, most carbohydrates are intrinsically T cell-independent antigens, which diminishes their efficacy as immunogens. The conversion of carbohydrate epitopes to peptide mimotopes is one means to overcome the T cell-independent nature of carbohydrate antigens because peptides have an absolute requirement for T cells. Although such conversion has great potential for the development of veterinarian and human vaccines, there are issues related to the use of peptide-based immunogens as functional surrogates. Some of these issues are fundamental, pertaining to how mimicry comes about at the molecular level, and some are application oriented, directed at elucidating important immunological mechanisms. In this article the potential and caveats of this technology regarding its application in vaccine discovery are analyzed.

Current and future applications of immunological attenuation via pegylation of cells and tissue

Prevention of immunological rejection of transplanted tissues is of crucial importance in transplantation medicine. Current procedures primarily use pharmacological agents such as cyclosporin, which, while effective, must be typically administered for the life of the individual. Furthermore, the drug-induced global immunosuppression of the patient predisposes the individual to infection and enhances their risk of developing certain forms of cancer. Hence, additional methods are needed to both enhance tissue engraftment and diminish the adverse effects of current immunosuppressive therapy. Studies from blood transfusion (i.e. a specialised form of cellular transplantation) suggest that covalent modification of cells and tissues with methoxypoly(ethylene glycol) [mPEG] can significantly diminish rejection episodes and may further enhance the induction of tolerance to donor tissues. The mechanisms underlying mPEG-mediated immunocamouflage are the loss of antigen recognition, impaired cell-cell interaction, and an inability of endogenous antibodies (e.g. immunoglobulin G) to effectively recognise and bind foreign epitopes. As a consequence of the global camouflage imparted by mPEG, the weak co-stimulation of alloreactive T cells may subsequently induce apoptosis, thus leading to tolerance. Initial studies on the transplantation of pegylated isogeneic rat pancreatic islets demonstrates that mPEG-derivatisation does not impair in vivo cellular signalling and function. Thus, in contrast to the pharmacological inhibition of the recipient's immune response, the mPEG-mediated immunocamouflage directly addresses the inherent antigenicity and immunogenicity of the donor tissue itself while leaving the recipient a fully competent immune system.

Tumour escape from immune surveillance through dendritic cell inactivation

Dendritic cells (DC) are central to the initiation of immunity. To induce immune reactivity, DC are recruited at the site of antigen expression, uptake antigens and migrate to secondary lymphoid organs while receiving activation signals delivered by pathogens, dying cells, and/or T cells. Tumours can escape the immune system by interfering with the migration of DC or by not providing the necessary activation signals. Moreover, tumours promote the secretion of factors that inhibit DC differentiation and functions. We will review the current knowledge of the physiopathology of DC in cancer, which paves the way for novel strategies of therapeutic intervention.

Immunotherapy for pancreatic cancer: current concepts

Despite advances in chemotherapy and surgical technique, patients with pancreatic cancer often succumb to local recurrence or metastatic spread. The need for new therapeutic strategies for this disease coupled with a better understanding of basic immunology have led to the development of novel anti-tumor vaccines. This review focuses on the historical development of tumor vaccines emphasizing the identification of potential pancreatic tumor antigens. The role of both B-cell and T-cell responses in tumor rejection will be reviewed. Methods for antigen presentation, including peptides, recombinant viral and bacterial vectors, dendritic cells, and whole cell approaches will be discussed. The use of immune adjuvants and improved methods of vaccine delivery will also be explored. The full potential for the immunotherapy of pancreatic cancer awaits the results of early phase clinical trials. The development of pancreatic cancer vaccines represents a useful paradigm for the translation of basic research into the clinical arena.

Autoreactivity, dynamic tuning and selectivity

The immune system adjusts its response to the context in which antigens, including self-antigens, are recognized. Recent observations support a conceptual framework for understanding how this may be achieved at the cellular and cell-population levels. At both levels, 'perturbations' elicit competition between excitation and de-excitation, resulting either in adaptation or in various responses. The responsiveness of individual cells is dynamically tuned, reflecting their recent experience. The tuning of T-cell activation thresholds by self-ligands facilitates positive selection and continuously regulates the level of autoreactivity in the periphery. Autoreactivity appears to be involved in regulation of the immune response, homeostasis, maintaining of the functional integrity of naïve and memory cells, and in other physiological functions.

Regulated gene expression in gene therapy

The original model of gene therapy, that of efficient delivery, durable transfer, and stable expression of transgenes to correct a gene defect underlying an inherited disease, is limited in light of improved understanding of the processes involved. Techniques that enable regulated expression of transgenes may enhance safety and allow us to regulate the timing and level of expression with a goal of precisely targeting a therapeutic level between the extremes of suboptimal and supraoptimal thresholds. Using regulated systems to control protein expression has practical and possibly essential roles for the success of safe and effective gene therapy in a number of clinical situations. Pharmacologically regulated gene expression is an evolving tool, and no individual system may be effective in all clinical applications.

Toxoplasma gondii and MHC-restricted antigen presentation: on degradation, transport and modulation

Resistance against Toxoplasma gondii, an obligate intracellular protozoan parasite surrounded by a parasitophorous vacuolar membrane, is mediated by the cellular arm of the immune system, namely CD8+ and CD4+ T cells. Thus, priming and activation of these cells by presentation of antigenic peptides in the context of major histocompatibility complex class I and class II molecules have to take place. This is despite the fact that the vacuolar membrane avoids fusion with the endocytic compartment and acts like a molecular sieve, restricting passive diffusion of larger molecules. This raises several cell biological and immunological questions which will be discussed in this review in the context of our current knowledge about major histocompatibility complex-restricted antigen presentation in other systems: (1) By which pathways are parasite-derived antigens presented to T cells? (2) Has the parasite evolved mechanisms to interfere with major histocompatibility complex-restricted antigen presentation in order to avoid immune recognition? (3) To what extent and by which mechanism is antigenic material, originating from the parasite, able to pass through the vacuolar membrane into the cytosol of the infected cell and is it then accessible to the antigen presentation machinery of the infected cell? (4) What are the actual antigen-presenting cells which prime specific T cells in lymphoid organs? An understanding of these mechanisms will not only provide new insights into the pathogenesis of Toxoplasma gondii and possibly other intravacuolar parasites, but will also improve vaccination strategies.

The relationship between major histocompatibility receptors and innate immunity in teleost fish

Studies of the innate immune system have recently shown that, in addition to its role in producing the primary response that slows down pathogens, it may also play an important role in initiating and directing the type of response that the adaptive immune system makes. These discoveries have shown a complex web of control containing new roles for the innate immune system in organizing responses of T-cell to antigens being presented by major histocompatibility receptors, as well as new roles for those receptors in innate immune responses. Both of these activities are managed through feedback networks involving elements of both the innate and adaptive immune system. This paper will discuss these newly discovered interactions and how they are influencing current theories regarding the initiation of adaptive immune responses. In particular, it will highlight the recent progress that is being made towards understanding these relationships in the immune systems of teleost fish.

The role of cytotoxicity in lymphocyte homeostasis

Several human inherited immune disorders lead to the same fatal lymphoproliferative syndrome, called the hemophagocytic syndrome. Through defective perforin expression or transport, these disorders highlight the determinant role of the secretory cytotoxic pathway in the regulation of the immune response and in lymphocyte homeostasis. In addition, new effectors of this secretory pathway have been identified.

The instructive role of dendritic cells on T cell responses: lineages, plasticity and kinetics

Dendritic cells are responsible for directing different types of T cell responses, from thymic negative selection to the generation of effector and memory cells and the induction of peripheral tolerance. Recent studies indicate that the dendritic cell lineage, the extent of recruitment into inflamed tissues and migration to lymph nodes, the nature of maturation stimuli and the kinetics of activation have a quantitative and qualitative impact on T cell stimulation, thus exerting an instructive control on T cell responses.

Interaction of T cells with APCs: the serial encounter model

Primary immune responses are initiated by specific physical interaction of antigen-specific T cells and professional antigen-presenting cells (APCs). Productive interactions can be a dynamic process that combines physical T-cell binding to APCs with vigorous crawling across and scanning of the APC surface, resulting in signal induction. After T-cell detachment, subsequent migratory contacts to the same or neighboring dendritic cells (DCs) allow the accumulation of sequential signals and interaction time. Here, we develop a serial encounter model of T-cell activation and discuss how the summation of multiple signals provides an efficient strategy to control an ongoing immune response.

Lymphoid neogenesis: de novo formation of lymphoid tissue in chronic inflammation through expression of homing chemokines

Chronic inflammation is a complex pathophysiological process with accumulation of mononuclear cells seen in response to invading pathogens, neoplastic transformation, or autoimmune recognition of self-antigens. The inflammatory process has evolved to facilitate effective elimination of pathogens and tumors and it is normally transient and turned off when the causative stimulus has been eliminated. Occasionally, however, the process is sustained for a long time and can lead to severe tissue damage. This is seen in organ-specific autoimmune diseases such as rheumatoid arthritis, Sjögren's syndrome, and Hashimoto's thyroiditis, but also in infectious diseases such as Helicobacter pylori-induced gastritis. Disturbingly, many of these chronic inflammatory diseases are associated with an increased risk for neoplastic transformation and development of lymphomas. This review summarizes experimental evidence suggesting that chronic inflammation involves ectopic de novo formation of organized lymphoid tissue and that this lymphoid neogenesis is regulated by expression of homing chemokines.

Self, intentionality, and immunological explanation

In this paper I propose that there are a number of conceptual reasons to preserve self-concepts in immunology. First, I contend that immunological language, including self-terminology, is neither genuinely anthropomorphic, nor perniciously teleological. Furthermore, although teleology associated with future-directed purposive intent is clearly inappropriate in biological contexts, a special type of teleology, intentionality-as-aboutness, needs to be present if there is to be functional explanation in immunology. Second, based on an analogy with the human self, a self comprised of both non-specific innate functions and somatic self-representation, I claim that self-terminology is very appropriate in immunological contexts. Finally, given the appropriateness of self-concepts in immunology, I suggest that the most satisfactory conceptual structure for self-nonself discrimination probably includes both innate and somatic mechanisms.

13C CP-MAS study of the gel phases of 1,2-dipalmitoylphosphatidylcholine

The multilamellar liposomes of the racemic 1,2-dipalmitoylphosphatidylcholine (DL-DPPC) existing in the various gel phases were investigated by means of the cross-polarization/magic angle spinning (CP-MAS) 13C-NMR. The intensity and the width of the 13C-NMR signals were found to depend to a large extent on temperature. In the metastable gel phase (L beta) signals from all carbon atoms are apparent, with the signals arising from the glycerol backbone significantly broader than those of the choline function. The signal from C-2 of the glycerol backbone undergoes additional broadening between 298 K and 307 K, and at 307 K its coalescence is observed. In the P beta' phase all carbon atoms give rise to relatively sharp separate resonance lines. In the liquid crystalline phase (L alpha) the signals from the choline function and from the terminal methyl groups of hydrocarbon are not observed in the spectrum. The recorded spectral changes are explained in terms of the rate of motional processes occurring in the lipid bilayer in different phases.