Aspergillus fumigatus peptides differentially express Th1 and Th2 cytokines

Molecular biology and immunology of fungal allergens

Fungi are non-chlorophyllus microorganisms, which constitutes the main source of outdoor and indoor allergens. The antigens present in the spores and fragments of hyphae induce allergic responses in sensitized patients. The frequently recognized fungi associated with asthma include Alternaria, Cladosporium, Aspergillus, and Penicillium. With the advent of molecular biology techniques a number of fungal genes encoding relevant allergens have been cloned and the expressed allergens purified and characterized. In this review, we have presented the recent developments, where recombinant allergens have been used in the precise diagnosis of fungal allergy. We have also discussed the role played by these allergens and the T- and B-cell epitopes in the immune mechanism in fungal allergy.

Complement-fixing anti-type VII collagen antibodies are induced in Th1-polarized lymph nodes of epidermolysis bullosa acquisita-susceptible mice

The environment encountered in secondary lymphoid organs (e.g., lymph nodes) influences the outcome of immune responses. Immunization of mice with type VII collagen, an adhesion protein expressed at the cutaneous basement membrane, induces experimental epidermolysis bullosa acquisita (EBA). In this model, clinical disease is associated with the H2s haplotype of the MHC found in SJL/J mice. Most other strains (e.g., BALB/c, C57BL/6, NZM2410/J) are resistant to clinical disease, despite autoantibody production. Comparison of autoantibody response in EBA-resistant and -susceptible mice showed an IgG2-dominated response in the latter. We hypothesized that EBA susceptibility is due to specific cytokine gene expression in draining lymph nodes (dLN). To challenge this hypothesis, EBA-susceptible (SJL/J) and -resistant (BALB/c, C57BL/6) mice were immunized with type VII collagen, followed by analysis of clinical phenotype, subclasses of circulating and tissue-bound autoantibodies, complement activation, and cytokine gene expression in dLN. Disease manifestation was associated with induction of complement-fixing autoantibodies, confirming previous observations. Furthermore, however, IFN-γ/IL-4 ratio in dLN of EBA-susceptible mice was significantly increased compared with EBA-resistant strains, suggesting a Th1 polarization. Immunization of H2s-congenic C57BL/6 mice (B6.SJL-H2s) led to Th1 polarization in dLN and clinical disease. In addition to their cytokine milieu, EBA-susceptible and -resistant mice also differed regarding the expression of FcγR on peripheral leukocytes, in which a higher FcγRIV expression in SJL/J and B6.SJL-H2s mice, compared with C57BL/6, was associated with skin lesions. In summary, blistering in experimental EBA is regulated by both adaptive (divergent class switch recombination due to polarized cytokine expression) and innate (FcγR expression) immune mechanisms.

Cultivated anti-Aspergillus T(H)1 cells

Invasive aspergillosis remains a serious complication in patients undergoing allogeneic stem cell transplantation. Since it became clear that lymphocytes provide a critical secondary defense against fungi, adoptive transfer of functionally active anti-Aspergillus T cells might be an option to restore adaptive immune effector mechanisms. Using the interferon (IFN)-gamma secretion assay, we isolated human activated T cells upon stimulation with a cellular extract of Aspergillus fumigatus. After a culturing period for 14 days, we could characterize these cells as T(H)1 cells, which also proliferated upon restimulation. The generated cells responded upon stimulation with antigens of A. flavus, A. niger and Penicillium chrysogenum, but not upon activation with Alternaria alternata and Candida albicans. In addition, the cultivated T cells were able to induce damage to A. fumigatus hyphae and showed a reduced alloreactivity compared to unselected CD4+ T cells. We further established a clinical-scale generation of anti-Aspergillus T cells. However, before performing clinical trials, open questions such as which patient population will benefit from adoptive immunotherapy with anti-Aspergillus T cells have to be addressed.

Immunity to Aspergillus fumigatus: the basis for immunotherapy and vaccination

Efficient responses to fungi require different mechanisms of immunity. Dendritic cells (DCs) are uniquely able to decode the fungus-associated information and translate it into qualitatively different T helper (Th) immune responses. Murine and human DCs phagocytose conidia and hyphae of Aspergillus fumigatus through distinct recognition receptors. The engagement of distinct receptors translates into disparate downstream signaling events, ultimately affecting cytokine production and co-stimulation. Adoptive transfer of different types of DCs activates protective and non-protective Th cells as well as regulatory T cells, ultimately affecting the outcome of the infection in mice with invasive aspergillosis. The infusion of fungus-pulsed or RNA-transfected DCs also accelerates recovery of functional antifungal Th 1 responses in mice with allogeneic hematopoietic stem cell transplantation. Patients receiving T cell-depleted allogeneic hematopoietic stem cell transplantation are unable to develop antigen-specific T cell responses soon after transplant due to defective DC functions. Our results suggest that the adoptive transfer of DCs may restore immunocompetence in hematopoietic stem cell transplantation by contributing to the educational program of T cells. Thus, the remarkable furictional plasticity of DCs can be exploited for the deliberate targeting of cells and pathways of cell-mediated immunity in response to the fungus.

Aspergillus antigens: which are important?

Aspergillus fumigatus is a ubiquitous fungus that causes a variety of diseases in man and animals. A number of protein, carbohydrate, and glycoprotein antigens have been identified from A. fumigatus. The diseases are diverse, and therefore are the antigens and their roles in causing or modulating the diseases. The induction and binding of antibodies and the interaction of antigen and various immune cells are of immense significance in the diagnosis and prognosis of the disease. In recent years, over 20 genes encoding A. fumigatus antigens have been cloned and the proteins expressed. Among these allergens, Asp f 1, f 2, f 3, f 4, and f 6 showed strong but diverse IgE binding with sera from different groups of patients. Results currently available suggest that Asp f 2, f 3, and f 6 together reacted with IgE from more patients with asthma and allergic bronchopulmonary aspergillosis (ABPA), although they are only marginally effective in demonstrating specific IgE in patients with cystic fibrosis and ABPA. The molecular structure of allergens also plays a major role in the immunological response in the allergic patients. Antigens can be engineered with less or more binding with IgE, and such antigens may have significant roles as specific reagents or as immunomodulators.

The contribution of animal models of aspergillosis to understanding pathogenesis, therapy and virulence

Animal models of aspergillosis have been used extensively to study various aspects of pathogenesis, innate and acquired host-response, disease transmission and therapy. Several different animal models of aspergillosis have been developed. Because aspergillosis is an important pulmonary disease in birds, avian models have been used successfully to study preventative vaccines. Studies done to emulate human disease have relied on models using common laboratory animal species. Guinea pig models have primarily been used in therapy studies of invasive pulmonary aspergillosis (IPA). Rabbits have been used to study IPA and systemic disease, as well as fungal keratitis. Rodent, particularly mouse, models of aspergillosis predominate as the choice for most investigators. The availability of genetically defined strains of mice, immunological reagents, cost and ease of handling are factors. Both normal and immunosuppressed animals are used routinely. These models have been used to determine efficacy of experimental therapeutics, comparative virulence of different isolates of Aspergillus, genes involved in virulence, and susceptibility to infection with Aspergillus. Mice with genetic immunological deficiency and cytokine gene-specific knockout mice facilitate studies of the roles cells, and cytokines and chemokines, play in host-resistance to Aspergillus. Overall, these models have been critical to the advancement of therapy, and our current understanding of pathogenesis and host-resistance.

Pathogenesis of allergic bronchopulmonary aspergillosis and an evidence-based review of azoles in treatment

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a complex condition that affects people with asthma and cystic fibrosis (CF). It results from exposure to the fungus Aspergillus fumigatus, which leads to worsening airway inflammation and progressive damage to the lungs. The aim of this review is to outline the pathogenesis of the disorder, diagnostic criteria and to discuss the use of anti-fungal agents in its treatment.

METHODS

The Cochrane library of systematic reviews and the Cochrane database of controlled trials were searched for controlled trials on ABPA and its treatment in both asthma and CF. In addition, articles included within the reviews were examined separately, and a separate search carried out using Medline.

RESULTS

A systematic review for the use of azole anti-fungal agents in ABPA was identified for their use in both CF and non-CF-related disease. The review of ABPA alone identified two randomized-controlled trials of itraconazole in chronic disease. These trials demonstrated improvements in symptoms and immune activation, but were short-term trials and failed to show a significant change in lung function. No trials were identified in CF.

CONCLUSIONS

The use of anti-fungal agents in ABPA seems to be a rational one, with short-term efficacy demonstrated for the use of itraconazole. Further investigations are required to identify individuals who will benefit most from treatment and to establish the correct dose and means of delivering treatment in ABPA. Longer-term studies are required to demonstrate that treatment modifies the progressive decline in lung function seen with the disease.

Use of a synthetic peptide epitope of Asp f 1, a major allergen or antigen of Aspergillus fumigatus, for improved immunodiagnosis of allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is an immunologically complex allergic disorder caused by the fungal pathogen Aspergillus fumigatus. Elevated levels of total immunoglobulin E (IgE), specific IgE, and IgG antibodies in sera are important immunodiagnostic criteria for ABPA. International reference standards or standardized immunodiagnostic assays are not available due to a lack of well-defined diagnostic antigens. The present study was carried out to identify and evaluate the immunodiagnostic relevance of synthetic epitopic peptides of Asp f 1, a major allergen, antigen, or cytotoxin of A. fumigatus. Five overlapping peptides were synthesized from the N terminus of Asp f 1, one of the potential immunodominant regions predicted by algorithmic programs. The 11-amino-acid synthetic peptide (P1) significantly inhibited both IgG binding (89.10% +/- 4.45%) and IgE binding (77.32% +/- 3.38%) of the standardized diagnostic antigen (SDA) (a well-defined pool of diagnostically relevant allergens and antigens of A. fumigatus). With a panel of sera of ABPA patients, allergic patients with skin test negativity to A. fumigatus, and healthy individuals, P1 showed a higher diagnostic efficiency than SDA (specific IgG, 100%; specific IgE, 98.3%). The diagnostic efficiency of P1 could be attributed to the presence of homologous epitopes in various immunodominant allergens or antigens of A. fumigatus. The ability of P1 to induce histamine release from sensitized mast cells and a Th2 type of cytokine profile in peripheral blood mononuclear cells of ABPA patients suggests its potential for use in intradermal testing. P1 could be further explored for development of a standardized, specific, and sensitive immunodiagnostic test for aspergillosis.

Fungal allergens

Many fungi are capable of causing IgE-mediated hypersensitivity in humans. However, the most predominant fungi implicated in allergy belong to the genera Aspergillus, Alternaria, Cladosporium, and Penicillium. Pure and relevant allergens are essential for diagnosis as well as for understanding the immunopathogenesis of the disease. Until recently, pure and standardizable antigens from fungi were not available. In recent years, many recombinant allergens have been produced by molecular cloning. Using these allergens, novel methods are being developed to improve diagnosis of mold-induced allergy. By understanding the immunopathogenesis of allergens, new avenues might open up leading to improved patient care, including immunotherapy and vaccination. This review covers the current status of fungal allergens, their role in reliable immunodiagnosis, and their probable use in immunotherapy and vaccination.

Aspergillosis. Pathogenesis, clinical manifestations, and therapy

Diseases caused by Aspergillus species are increasing in importance, especially among immunocompromised hosts. Clinical manifestations are variable, ranging from allergic to invasive disease, largely depending on the status of the host's immune system. This article focuses on the pathogenesis and clinical manifestations of diseases caused by Aspergillus species, with more detailed discussion on therapy of the most morbid manifestation, invasive aspergillosis.

Animal models of allergic bronchopulmonary aspergillosis

Among the allergic fungi, Aspergillus fumigatus, a saprophytic mold, distributed widely in the environment is a frequently recognized etiologic agent in a number of allergic conditions. Among the different allergic diseases caused by this fungus, allergic bronchopulmonary aspergillosis (ABPA) is by far the most significant one. The immunopathogenesis of this disease is not fully understood. Although several immunomodulatory treatments are available for allergic disease, none of them are applicable or relevant or useful in fungal induced allergy. It is essential to understand the pathogenesis of the disease including the antigen induced immunoregulation and the resulting factors, such as cytokine, chemokines, pathways activating factors, inflammatory and airway remodeling factors need to be understood for intervening with appropriate treatment. Animal models are essential in understanding these features of the disease. Several models of allergic aspergillosis have been developed in recent years in various animals. However, murine models have been studied more carefully and extensively. The exposure to antigen in mice leads to allergy very similar to ABPA with high IgE, elevated peripheral blood and lung eosinophils, pulmonary inflammation, and airway hyperreactivity. The role of various cytokines and chemokines and their receptors were also studied. In addition, immunotherapy and vaccination have been attempted in recent years using the murine model of ABPA. This review covers the murine model of Aspergillus induced allergy and asthma and presented critically our current understanding of the subject and the potential application of such a model in future for developing treatment modalities.

Vaccination of mice against invasive aspergillosis with recombinant Aspergillus proteins and CpG oligodeoxynucleotides as adjuvants

In a murine model of invasive pulmonary aspergillosis, dendritic cells (DCs) pulsed with Aspergillus antigens induced the activation of CD4(+) Th1 cells capable of conferring resistance to the infection. Here we show that the combined, local delivery of unmethylated CpG oligodeoxynucleotides (ODNs) and the Asp f 16 Aspergillus allergen resulted in the functional maturation and activation of airway DCs capable of inducing Th1 priming and resistance to the fungus. Therefore, ODNs act as a potent adjuvant for the vaccine-induced protection against the fungus by promoting dominant Th1 response to Aspergillus antigens and allergens.

T cell proliferation and cytokine secretion to T cell epitopes of Asp f 2 in ABPA patients

The pathogenesis of allergic bronchopulmonary aspergillosis (ABPA) involves specific cytokines secreted by lymphocytes in response to Aspergillus fumigatus (Af) allergens. To gain information about the lymphoproliferative response and cytokine production against a major Af allergen, Asp f 2, we studied Asp-f-2-specific T cell clones (TCCs) from ABPA patients. TCCs were stimulated with rAsp f 2, its deletion mutants, and synthetic peptides to identify the T cell epitope(s) and to understand cytokine production. PBMCs from four of five ABPA patients showed proliferation in response to Asp f 2. Three TCCs from one patient showed higher IL-5 secretion compared to IL-4 and IFN-gamma. Two TCCs from the second patient showed a mixed Th1/Th2 response, as evidenced by production of IL-4, IL-5, and IFN-gamma. An epitope from the N-terminal region of Asp f 2 induced only IL-5 secretion. High IL-5 secretion might explain the marked eosinophilia observed in ABPA patients.

[Cytotoxic activity and cytokine gene induction of Asp-hemolysin to vascular endothelial cells]

We examined the effects of Asp-hemolysin from Aspergillus fumigatus Fresenius-Muramatsu strain on the viability and cytokine gene expression of human umbilical vein endothelial cells (HUVEC). The cell viability of HUVEC was reduced to 50% by 100 micrograms/ml of Asp-hemolysin. However, lower concentration of Asp-hemolysin (< 30 micrograms/ml) had no effect on the cell viability. The mRNA expression of such cytokines as tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta, IL-6, IL-8 and granulocyte-macrophage colony stimulating factor (GM-CSF) were also observed in HUVEC cultured with 30 micrograms/ml of Asp-hemolysin.

Allergic bronchopulmonary aspergillosis: new concepts of pathogenesis and treatment

Allergic bronchopulmonary aspergillosis (ABPA) is a condition that results from a hypersensitivity reaction to the fungus Aspergillus fumigatus. The purpose of the present review is to examine the pathogenesis of this condition and the evidence for treatments available. Allergic bronchopulmonary aspergillosis is characterized by an intense airway inflammation with eosinophils and the formation of mucus plugs. Clinically, there are periods of exacerbation and remission that may lead to proximal bronchiectasis and fibrotic lung disease. New evidence confirms the role of intense airway inflammation with eosinophils, but also suggests a role for interleukin (IL)-8/neutrophil-mediated inflammation in this process, and the potential deficiency of anti-inflammatory cytokines such as reduced IL-10. Treatment for ABPA has so far focused on corticosteroids to suppress eosinophilic airway inflammation. An expanding knowledge of the pathology of ABPA also suggests other therapies may be of potential benefit, particularly the use of azole antifungal agents. Allergic bronchopulmonary aspergillosis is itself an important complication of asthma and cystic fibrosis. A greater understanding of the condition is required to improve management and well-designed clinical trials need to be carried out to critically assess new and current treatments. In addition, the information gained from the studies of its pathogenesis has the potential to benefit our understanding of the disease processes in asthma and bronchiectasis.

T cell vaccination in mice with invasive pulmonary aspergillosis

Aspergillus fumigatus, an opportunistic fungal pathogen, is responsible for multiple airway diseases of an allergic and a nonallergic nature. In a murine model of invasive pulmonary aspergillosis, resistance is associated with a decreased lung inflammatory pathology and the occurrence of an IL-12-dependent Th1-type reactivity that are both impaired by IL-4. In the present study we assess the ability of Aspergillus crude culture filtrate Ags and the recombinant allergen Asp f 2 to induce protective antifungal responses in mice with invasive pulmonary aspergillosis. Similar to what occurred upon nasal exposure to viable A. fumigatus conidia, treatment of immunocompetent mice with Aspergillus crude culture filtrate Ags resulted in the development of local and peripheral protective Th1 memory responses, mediated by Ag-specific CD4+ T cells producing IFN-gamma and IL-2 capable of conferring protection upon adoptive transfer to naive recipients. Protective Th1 responses could not be observed in mice deficient of IFN-gamma or IL-12 and did not occur in response to Asp f 2, which, on the contrary, elicited high level production of inhibitory IL-4. The results show that Ags of Aspergillus exist with the ability to induce both Th1- and Th2-type reactivity during infection, a finding that suggests a possible mechanism through which potentially protective immune responses are inhibited in mice with the infection. However, the occurrence of Th1-mediated resistance upon vaccination with Aspergillus crude culture filtrate Ags, suggests the existence of fungal Ags useful as a candidate vaccine against invasive pulmonary aspergillosis.

Fungal allergens and peptide epitopes

Fungal allergens represent a major cause of atopic disorders. Immunochemical and molecular characterization of fungal allergens has been hampered by the lack of pure proteins and to inherent variation among fungal proteins and in their poor yields. With the advent of molecular biology techniques, a number of allergens have been cloned, sequenced, and expressed from a variety of fungal species. The knowledge of the primary, secondary, and tertiary structures of these allergens, the immunodominant regions of these proteins, and their interaction with T and B-cell epitopes, results in better understanding of the molecular mechanisms of allergy and may provide avenues of immunologic intervention to treat patients. The present review deals with the current understanding of fungal allergen epitopes.

Intravenous injection of major and cryptic peptide epitopes of ribotoxin, Asp f 1 inhibits T cell response induced by crude Aspergillus fumigatus antigens in mice

Aspergillus fumigatus, a ubiquitous fungus, is implicated in the pathogenesis of a number of clinically different allergic diseases in man. Peptide-based immunotherapy may offer an alternative in patient care and management. The purpose of this study was to evaluate the role of T cell epitopes of A. fumigatus ribotoxin, Asp f 1 in inducing tolerance in mice exposed to A. fumigatus antigen. The epitope analysis in BALB/c mice using synthetic peptides of Asp f 1 demonstrated both cryptic and dominant epitopes detected from 42 through 54 and 155 through 167 aa, accordingly. Intravenous injection of these peptides markedly inhibited the response induced by the exposure to crude A. fumigatus extract in mice as evidenced by the in vitro interleukin-2 (IL-2) production and proliferation of T-lymphocytes. Cytokine transcription studies indicate that, when stimulated with the peptides in immunogenic conditions, the major peptide (aa 155-167) specific T cell clone produced only IFN-gamma, but not IL-4. The ability of both dominant and cryptic peptide epitopes of a single molecule to induce tolerance against the immune response to a multi-molecular allergen complex has significant implication for peptide-based immunotherapy.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

IgE down regulation and cytokine induction by Aspergillus antigens in human allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA), occurring primarily in patients with asthma or cystic fibrosis (CF), is a hypersensitivity reaction to Aspergillus fumigatus (Af), and is characterized by increased serum IgE levels and peripheral blood and pulmonary eosinophilia. We evaluated the IgE and cytokine profile in ABPA through enzyme-linked immunosorbent assay (ELISA), and evaluated eosinophil activity with the eosinophil peroxidase (EPO) assay. IgE and cytokines were measured in supernatants from cultures of peripheral blood mononuclear cells (PBMC) from three subject groups: ABPA patients, patients with asthma, and healthy individuals. All cultures for the three subject groups were studied in the presence and absence of two purified Af antigens (the 35-kD antigen and heat shock protein 1). We found that increased in vitro levels of IgE in unstimulated PBMC culture supernatants correlated significantly with serum IgE concentrations in ABPA patients. We measured a decrease in IgE levels of up to 75% of baseline values in supernatants from PBMC cultured with Af antigens. Interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) concentrations in cultures with Af were increased in ABPA, whereas concentrations of IL-4 did not differ in the three subject groups. An inverse relation was noted between the changes in IgE and IFN-gamma measured in 4 of 5 ABPA patients. The PBMC supernatants also promoted EPO activity in purified eosinophils from ABPA patients, and to a lesser extent in purified eosinophils from healthy subjects. These results show that the 35-kD antigen and HSP1 from Af downregulate IgE in vitro but are capable of inducing eosinophilia in ABPA. Further studies could result in the characterization of epitopes leading to these disparate effects. An identification of the IgE-down-regulating epitopes in Af antigens might have therapeutic significance.

Immunodominant peptide epitopes of allergen, Asp f 1 from the fungus Aspergillus fumigatus

Aspergillus fumigatus ribotoxin Asp f 1 is a major allergen with IgE binding activity to serum of a majority of patients with allergic bronchopulmonary aspergillosis (ABPA). The IgE binding epitopes or the T-cell stimulatory peptides of this molecule have not been studied. In the present investigation, we have synthesized linear decapeptides spanning the whole molecule of Asp f 1 and analyzed their IgE binding properties. We have also synthesized peptides based on their possible T-cell stimulatory properties and studied the stimulation of peripheral blood mononuclear cells from ABPA patients and normal controls. Several peptides demonstrated distinct IgE antibody binding response against sera from ABPA patients and proliferative response against peripheral blood mononuclear cells from the patients. From the results, it can be concluded that the carboxy-terminal region of Asp f 1 representing amino acid residues 115-149 involved in both humoral and cell mediated immunoresponses in ABPA.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.