Arabidopsis heterotrimeric G-protein regulates cell wall defense and resistance to necrotrophic fungi

The Arabidopsis heterotrimeric G-protein controls defense responses to necrotrophic and vascular fungi. The agb1 mutant impaired in the Gβ subunit displays enhanced susceptibility to these pathogens. Gβ/AGB1 forms an obligate dimer with either one of the Arabidopsis Gγ subunits (γ1/AGG1 and γ2/AGG2). Accordingly, we now demonstrate that the agg1 agg2 double mutant is as susceptible as agb1 plants to the necrotrophic fungus Plectosphaerella cucumerina. To elucidate the molecular basis of heterotrimeric G-protein-mediated resistance, we performed a comparative transcriptomic analysis of agb1-1 mutant and wild-type plants upon inoculation with P. cucumerina. This analysis, together with metabolomic studies, demonstrated that G-protein-mediated resistance was independent of defensive pathways required for resistance to necrotrophic fungi, such as the salicylic acid, jasmonic acid, ethylene, abscisic acid, and tryptophan-derived metabolites signaling, as these pathways were not impaired in agb1 and agg1 agg2 mutants. Notably, many mis-regulated genes in agb1 plants were related with cell wall functions, which was also the case in agg1 agg2 mutant. Biochemical analyses and Fourier Transform InfraRed (FTIR) spectroscopy of cell walls from G-protein mutants revealed that the xylose content was lower in agb1 and agg1 agg2 mutants than in wild-type plants, and that mutant walls had similar FTIR spectratypes, which differed from that of wild-type plants. The data presented here suggest a canonical functionality of the Gβ and Gγ1/γ2 subunits in the control of Arabidopsis immune responses and the regulation of cell wall composition.

New insights into the regulation of NADPH oxidase dependent reactive oxygen species signaling during the plant immune response

Las NADPH oxidasas de plantas, denominadas “respiratory burst oxidase homologues” (RBOHs), producen especies reactivas del oxígeno (ROS) que median un amplio rango de funciones. En la célula vegetal, el ajuste preciso de la producción de ROS aporta la especificidad de señal para generar una respuesta apropiada ante las amenazas ambientales. RbohD y RbohF, dos de los diez genes Rboh de Arabidopsis, son pleiotrópicos y median diversos procesos fisiológicos en respuesta a patógenos. El control espacio-temporal de la expresión de los genes RbohD y RbohF podría ser un aspecto crítico para determinar la multiplicidad de funciones de estas oxidasas. Por ello, generamos líneas transgénicas de Arabidopsis con fusiones de los promoters de RbohD y RbohF a los genes delatores de la B-glucuronidasa y la luciferasa. Estas líneas fueron empleadas para revelar el patrón de expresión diferencial de RbohD y RbohF durante la respuesta inmune de Arabidopsis a la bacteria patógena Pseudomonas syringae pv. tomato DC3000, el hongo necrótrofo Plectosphaerella cucumerina y en respuesta a señales relacionadas con la respuesta inmune. Nuestros experimentos revelan un patrón de expresión diferencial de los promotores de RbohD y RbohF durante el desarrollo de la planta y en la respuesta inmune de Arabidopsis. Además hemos puesto de manifiesto que existe una correlación entre el nivel de actividad de los promotores de RbohD y RbohF con la acumulación de ROS y el nivel de muerte celular en respuesta a patógenos. La expression de RbohD y RbohF también es modulada de manera diferencial en respuesta a patrones moleculares asociados a patógenos (PAMPs) y por ácido abscísico (ABA). Cabe destacar que, mediante una estrategia de intercambio de promotores, hemos revelado que la región promotora de RbohD, es necesaria para dirigir la producción de ROS en respuesta a P. cucumerina. Adicionalmente, la activación del promotor de RbohD en respuesta al aislado de P. cucumerina no adaptado a Arabidopsis 2127, nos llevó a realizar ensayos de susceptibilidad con el doble mutante rbohD rbohF que han revelado un papel desconocido de estas oxidasas en resistencia no-huesped. La interacción entre la señalización dependiente de las RBOHs y otros componentes de la respuesta inmune de plantas podría explicar también las distintas funciones que median estas oxidasas en relación con la respuesta inmune. Entre la gran cantidad de señales coordinadas con la actividad de las RBOHs, existen evidencias genéticas y farmacológicas que indican que las proteínas G heterotriméricas están implicadas en algunas de las rutas de señalización mediadas por ROS derivadas de los RBOHs en respuesta a señales ambientales. Por ello hemos estudiado la relación entre estas RBOH-NADPH oxidasas y AGB1, la subunidad β de las proteínas G heterotriméricas en la respuesta inmune de Arabidopsis. Análisis de epistasis indican que las proteínas G heterotriméricas están implicadas en distintas rutas de señalización en defensa mediadas por las RBOHs. Nuestros resultados ilustran la relación compleja entre la señalización mediada por las RBOHs y las proteínas G heterotriméricas, que varía en función de la interacción planta-patógeno analizada. Además, hemos explorado la posible asociación entre AGB1 con RBOHD y RBOHF en eventos tempranos de la respuesta immune. Cabe señalar que experimentos de coímmunoprecipitación apuntan a una posible asociación entre AGB1 y la kinasa citoplasmática reguladora de RBOHD, BIK1. Esto indica un posible mecanismo de control de la función de esta NADPH oxidase por AGB1. En conjunto, estos datos aportan nuevas perspectivas sobre cómo, a través del control transcripcional o mediante la interacción con las proteínas G heterotriméricas, las NADPH oxidases de plantas median la producción de ROS y la señalización por ROS en la respuesta inmune. Nuestro trabajo ejemplifica cómo la regulación diferencial de dos miembros de una familia multigénica, les permite realizar distintas funciones fisiológicas especializadas usando un mismo mecanismo enzimático. ABSTRACT The plant NADPH oxidases, termed respiratory burst oxidase homologues (RBOHs), produce reactive oxygen species (ROS) which mediate a wide range of functions. Fine tuning this ROS production provides the signaling specificity to the plant cell to produce the appropriate response to environmental threats. RbohD and RbohF, two of the ten Rboh genes present in Arabidopsis, are pleiotropic and mediate diverse physiological processes in response to pathogens. One aspect that may prove critical to determine the multiplicity of functions of RbohD and RbohF is the spatio-temporal control of their gene expression. Thus, we generated Arabidopsis transgenic lines with RbohD- and RbohF-promoter fusions to the β-glucuronidase and the luciferase reporter genes. These transgenics were employed to reveal RbohD and RbohF promoter activity during Arabidopsis immune response to the pathogenic bacterium Pseudomonas syringae pv tomato DC3000, the necrotrophic fungus Plectosphaerella cucumerina and in response to immunity-related cues. Our experiments revealed a differential expression pattern of RbohD and RbohF throughout plant development and during Arabidopsis immune response. Moreover, we observed a correlation between the level of RbohD and RbohF promoter activity, the accumulation of ROS and the amount of cell death in response to pathogens. RbohD and RbohF gene expression was also differentially modulated by pathogen associated molecular patterns and abscisic acid. Interestingly, a promoter-swap strategy revealed the requirement for the promoter region of RbohD to drive the production of ROS in response to P. cucumerina. Additionally, since the RbohD promoter was activated during Arabidopsis interaction with a non-adapted P. cucumerina isolate 2127, we performed susceptibility tests to this fungal isolate that uncovered a new role of these oxidases on non-host resistance. The interplay between RBOH-dependent signaling with other components of the plant immune response might also explain the different immunity-related functions mediated by these oxidases. Among the plethora of signals coordinated with RBOH activity, pharmacological and genetic evidence indicates that heterotrimeric G proteins are involved in some of the signaling pathways mediated by RBOH–derived ROS in response to environmental cues. Therefore, we analysed the interplay between these RBOH-NADPH oxidases and AGB1, the Arabidopsis β-subunit of heterotrimeric G proteins during Arabidopsis immune response. We carried out epistasis studies that allowed us to test the implication of AGB1 in different RBOH-mediated defense signaling pathways. Our results illustrate the complex relationship between RBOH and heterotrimeric G proteins signaling, that varies depending on the type of plant-pathogen interaction. Furthermore, we tested the potential association between AGB1 with RBOHD and RBOHF during early immunity. Interestingly, our co-immunoprecipitation experiments point towards an association of AGB1 and the RBOHD regulatory kinase BIK1, thus providing a putative mechanism in the control of the NADPH oxidase function by AGB1. Taken all together, these studies provide further insights into the role that transcriptional control or the interaction with heterotrimeric G-proteins have on RBOH-NADPH oxidase-dependent ROS production and signaling in immunity. Our work exemplifies how, through a differential regulation, two members of a multigenic family achieve specialized physiological functions using a common enzymatic mechanism.

Analysis of the Drosophila host defense in domino mutant larvae, which are devoid of hemocytes

We have analyzed the Drosophila immune response in domino mutant larvae, which are devoid of blood cells. The domino mutants have a good larval viability, but they die as prepupae. We show that, on immune challenge, induction of the genes encoding antimicrobial peptides in the fat body is not affected significantly in the mutant larvae, indicating that hemocytes are not essential in this process. The hemocoele of domino larvae contains numerous live microorganisms, the presence of which induces a weak antimicrobial response in the fat body. A full response is observed only after septic injury. We propose that the fat body cells are activated both by the presence of microorganisms and by injury and that injury potentiates the effect of microorganisms. Survival experiments after an immune challenge showed that domino mutants devoid of blood cells maintain a wild-type resistance to septic injury. This resistance was also observed in mutant larvae in which the synthesis of antibacterial peptides is impaired (immune deficiency larvae) and in mutants that are deficient for humoral melanization (Black cells larvae). However, if domino was combined with either the immune deficiency or the Black cell mutation, the resistance to septic injury was reduced severely. These results establish the relevance of the three immune reactions: phagocytosis, synthesis of antibacterial peptides, and melanization. By working in synergy, they provide Drosophila a highly effective defense against injury and/or infection.

The GATA factor Serpent is required for the onset of the humoral immune response in Drosophila embryos

Innate immunity in Drosophila is characterized by the inducible expression of antimicrobial peptides. We have investigated the development and regulation of immune responsiveness in Drosophila embryos after infection. Immune competence, as monitored by the induction of Cecropin A1-lacZ constructs, was observed first in the embryonic yolk. This observation suggests that the yolk plays an important role in the humoral immune response of the developing embryo by synthesizing antimicrobial peptides. Around midembryogenesis, the response in the yolk was diminished. Simultaneously, Cecropin expression became inducible in a large number of cells in the epidermis, demonstrating that late-stage embryos can synthesize their own antibiotics in the epidermis. This production likely serves to provide the hatching larva with an active antimicrobial barrier and protection against systemic infections. Cecropin expression in the yolk required the presence of a GATA site in the promoter as well as the involvement of the GATA-binding transcription factor Serpent (dGATAb). In contrast, neither the GATA site nor Serpent were necessary for Cecropin expression in the epidermis. Thus, the inducible immune responses in the yolk and in the epidermis can be uncoupled and call for distinct sets of transcription factors. Our data suggest that Serpent is involved in the distinction between a systemic response in the yolk/fat body and a local immune response in epithelial cells. In addition, the present study shows that signal transduction pathways controlling innate and epithelial defense reactions can be dissected genetically in Drosophila embryos.

Nitric oxide and salicylic acid signaling in plant defense

Salicylic acid (SA) plays a critical signaling role in the activation of plant defense responses after pathogen attack. We have identified several potential components of the SA signaling pathway, including (i) the H2O2-scavenging enzymes catalase and ascorbate peroxidase, (ii) a high affinity SA-binding protein (SABP2), (iii) a SA-inducible protein kinase (SIPK), (iv) NPR1, an ankyrin repeat-containing protein that exhibits limited homology to IκBα and is required for SA signaling, and (v) members of the TGA/OBF family of bZIP transcription factors. These bZIP factors physically interact with NPR1 and bind the SA-responsive element in promoters of several defense genes, such as the pathogenesis-related 1 gene (PR-1). Recent studies have demonstrated that nitric oxide (NO) is another signal that activates defense responses after pathogen attack. NO has been shown to play a critical role in the activation of innate immune and inflammatory responses in animals. Increases in NO synthase (NOS)-like activity occurred in resistant but not susceptible tobacco after infection with tobacco mosaic virus. Here we demonstrate that this increase in activity participates in PR-1 gene induction. Two signaling molecules, cGMP and cyclic ADP ribose (cADPR), which function downstream of NO in animals, also appear to mediate plant defense gene activation (e.g., PR-1). Additionally, NO may activate PR-1 expression via an NO-dependent, cADPR-independent pathway. Several targets of NO in animals, including guanylate cyclase, aconitase, and mitogen-activated protein kinases (e.g., SIPK), are also modulated by NO in plants. Thus, at least portions of NO signaling pathways appear to be shared between plants and animals.

Origins of immunity: Relish, a compound Rel-like gene in the antibacterial defense of Drosophila.

NF-kappa B/Rel transcription factors are central regulators of mammalian immunity and are also implicated in the induction of cecropins and other antibacterial peptides in insects. We identified the gene for Relish, a compound Drosophila protein that, like mammalian p105 and p100, contains both a Rel homology domain and an I kappa B-like domain. Relish is strongly induced in infected flies, and it can activate transcription from the Cecropin A1 promoter. A Relish transcript is also detected in early embryos, suggesting that it acts in both immunity and embryogenesis. The presence of a compound Rel protein in Drosophila indicates that similar proteins were likely present in primordial immune systems and may serve unique signaling functions.

Structure-activity analysis of thanatin, a 21-residue inducible insect defense peptide with sequence homology to frog skin antimicrobial peptides.

Immune challenge to the insect Podisus maculiventris induces synthesis of a 21-residue peptide with sequence homology to frog skin antimicrobial peptides of the brevinin family. The insect and frog peptides have in common a C-terminally located disulfide bridge delineating a cationic loop. The peptide is bactericidal and fungicidal, exhibiting the largest antimicrobial spectrum observed so far for an insect defense peptide. An all-D-enantiomer is nearly inactive against Gram-negative bacteria and some Gram-positive strains but is fully active against fungi and other Gram-positive bacteria, suggesting that more than one mechanism accounts for the antimicrobial activity of this peptide. Studies with truncated synthetic isoforms underline the role of the C-terminal loop and flanking residues for the activity of this molecule for which we propose the name thanatin.

Immune Response In Thyroid Cancer: Widening The Boundaries.

The association between thyroid cancer and thyroid inflammation has been repeatedly reported and highly debated in the literature. In fact, both molecular and epidemiological data suggest that these diseases are closely related and this association reinforces that the immune system is important for thyroid cancer progression. Innate immunity is the first line of defensive response. Unlike innate immune responses, adaptive responses are highly specific to the particular antigen that induced them. Both branches of the immune system may interact in antitumor immune response. Major effector cells of the immune system that directly target thyroid cancer cells include dendritic cells, macrophages, polymorphonuclear leukocytes, mast cells, and lymphocytes. A mixture of immune cells may infiltrate thyroid cancer microenvironment and the balance of protumor and antitumor activity of these cells may be associated with prognosis. Herein, we describe some evidences that immune response may be important for thyroid cancer progression and may help us identify more aggressive tumors, sparing the vast majority of patients from costly unnecessary invasive procedures. The future trend in thyroid cancer is an individualized therapy.

Urothelial Carcinogen Resistance Driven By Stronger Toll-like Receptor 2 (tlr2) And Uroplakin Iii (up Iii) Defense Mechanisms: A New Model.

The objective of the study was to illustrate the applicability and significance of the novel Lewis urothelial cancer model compared to the classic Fisher 344. Fischer 344 and Lewis females rats, 7 weeks old, were intravesical instilled N-methyl-N-nitrosourea 1.5 mg/kg every other week for a total of four doses. After 15 weeks, animals were sacrificed and bladders analyzed: histopathology (tumor grade and stage), immunohistochemistry (apoptotic and proliferative indices) and blotting (Toll-like receptor 2-TLR2, Uroplakin III-UP III and C-Myc). Control groups received placebo. There were macroscopic neoplastic lesions in 20 % of Lewis strain and 70 % of Fischer 344 strain. Lewis showed hyperplasia in 50 % of animals, normal bladders in 50 %. All Fischer 344 had lesions, 20 % papillary hyperplasia, 30 % dysplasia, 40 % neoplasia and 10 % squamous metaplasia. Proliferative and apoptotic indices were significantly lower in the Lewis strain (p < 0.01). The TLR2 and UP III protein levels were significantly higher in Lewis compared to Fischer 344 strain (70.8 and 46.5 % vs. 49.5 and 16.9 %, respectively). In contrast, C-Myc protein levels were significantly higher in Fischer 344 (22.5 %) compared to Lewis strain (13.7 %). The innovative Lewis carcinogen resistance urothelial model represents a new strategy for translational research. Preservation of TLR2 and UP III defense mechanisms might drive diverse urothelial phenotypes during carcinogenesis in differently susceptible individuals.

Oropouche Virus Infection And Pathogenesis Is Restricted By Mavs, Irf-3, Irf-7, And Type I Ifn Signaling Pathways In Non-myeloid Cells.

Oropouche virus (OROV) is a member of the Orthobunyavirus genus in the Bunyaviridae family and a prominent cause of insect-transmitted viral disease in Central and South America. Despite its clinical relevance, little is known about OROV pathogenesis. To define the host defense pathways that control OROV infection and disease, we evaluated OROV pathogenesis and immune responses in primary cells and mice that were deficient in the RIG-I-like receptor signaling pathway (MDA5, RIG-I, or MAVS), downstream regulatory transcription factors (IRF-3 or IRF-7), IFN-β, or the receptor for type I IFN signaling (IFNAR). OROV replicated to higher levels in primary fibroblasts and dendritic cells lacking MAVS signaling, the transcription factors IRF-3 and IRF-7, or IFNAR. In mice, deletion of IFNAR, MAVS, or IRF-3 and IRF-7 resulted in uncontrolled OROV replication, hypercytokinemia, extensive liver damage, and death whereas wild-type (WT) congenic animals failed to develop disease. Unexpectedly, mice with a selective deletion of IFNAR on myeloid cells (CD11c Cre(+) Ifnar(f/f) or LysM Cre(+) Ifnar(f/f)) did not sustain enhanced disease with OROV or La Crosse virus, a closely related encephalitic orthobunyavirus. In bone marrow chimera studies, recipient irradiated Ifnar(-/-) mice reconstituted with WT hematopoietic cells sustained high levels of OROV replication and liver damage, whereas WT mice reconstituted with Ifnar(-/-) bone marrow were resistant to disease. Collectively, these results establish a dominant protective role for MAVS, IRF-3 and IRF-7, and IFNAR in restricting OROV virus infection and tissue injury, and suggest that IFN signaling in non-myeloid cells contributes to the host defense against orthobunyaviruses. Oropouche virus (OROV) is an emerging arthropod-transmitted orthobunyavirus that causes episodic outbreaks of a debilitating febrile illness in humans in countries of South and Central America. The continued expansion of the range and number of its arthropod vectors increases the likelihood that OROV will spread into new regions. At present, the pathogenesis of OROV in humans or other vertebrate animals remains poorly understood. To define cellular mechanisms of control of OROV infection, we performed infection studies in a series of primary cells and mice that were deficient in key innate immune genes involved in pathogen recognition and control. Our results establish that a MAVS-dependent type I IFN signaling pathway has a dominant role in restricting OROV infection and pathogenesis in vivo.

Immune cells and oxidative stress in the endotoxin tolerance mouse model

Sepsis is a systemic inflammatory response that can lead to tissue damage and death. In order to increase our understanding of sepsis, experimental models are needed that produce relevant immune and inflammatory responses during a septic event. We describe a lipopolysaccharide tolerance mouse model to characterize the cellular and molecular alterations of immune cells during sepsis. The model presents a typical lipopolysaccharide tolerance pattern in which tolerance is related to decreased production and secretion of cytokines after a subsequent exposure to a lethal dose of lipopolysaccharide. The initial lipopolysaccharide exposure also altered the expression patterns of cytokines and was followed by an 8- and a 1.5-fold increase in the T helper 1 and 2 cell subpopulations. Behavioral data indicate a decrease in spontaneous activity and an increase in body temperature following exposure to lipopolysaccharide. In contrast, tolerant animals maintained production of reactive oxygen species and nitric oxide when terminally challenged by cecal ligation and puncture (CLP). Survival study after CLP showed protection in tolerant compared to naive animals. Spleen mass increased in tolerant animals followed by increases of B lymphocytes and subpopulation Th1 cells. An increase in the number of stem cells was found in spleen and bone marrow. We also showed that administration of spleen or bone marrow cells from tolerant to naive animals transfers the acquired resistance status. In conclusion, lipopolysaccharide tolerance is a natural reprogramming of the immune system that increases the number of immune cells, particularly T helper 1 cells, and does not reduce oxidative stress.

The effects of nitric oxide on the immune response during giardiasis

Nitric oxide (NO) is a free radical synthesized from L-arginine by different isoforms NO-synthases. NO possesses multiple and complex biological functions. NO is an important mediator of homeostasis, and changes in its generation or actions can contribute or not to pathological states. The knowledge of effects of NO has been not only important to our understanding of immune response, but also to new tools for research and treatment of various diseases. Knowing the importance of NO as inflammatory mediator in diverse infectious diseases, we decided to develop a revision that shows the participation/effect of this mediator in immune response induced against Giardia spp. Several studies already demonstrated the participation of NO with microbicidal and microbiostatic activity in giardiasis. On the other hand, some works report that Giardia spp. inhibit NO production by consuming the intermediate metabolite arginine. In fact, studies in vitro showed that G. lamblia infection of human intestinal epithelial cells had reduced NO production. This occurs due to limited offer of the crucial substrate arginine (essential aminoacid for NO production), consequently reducing NO production. Therefore, the balance between giardial arginine consumption and epithelial NO production could contribute to the variability of the duration and severity of infections by this ubiquitous parasite.

Unexpected Diversity of Cellular Immune Responses against Nef and Vif in HIV-1-Infected Patients Who Spontaneously Control Viral Replication

Background: HIV-1-infected individuals who spontaneously control viral replication represent an example of successful containment of the AIDS virus. Understanding the anti-viral immune responses in these individuals may help in vaccine design. However, immune responses against HIV-1 are normally analyzed using HIV-1 consensus B 15-mers that overlap by 11 amino acids. Unfortunately, this method may underestimate the real breadth of the cellular immune responses against the autologous sequence of the infecting virus. Methodology and Principal Findings: Here we compared cellular immune responses against nef and vif-encoded consensus B 15-mer peptides to responses against HLA class I-predicted minimal optimal epitopes from consensus B and autologous sequences in six patients who have controlled HIV-1 replication. Interestingly, our analysis revealed that three of our patients had broader cellular immune responses against HLA class I-predicted minimal optimal epitopes from either autologous viruses or from the HIV-1 consensus B sequence, when compared to responses against the 15-mer HIV-1 type B consensus peptides. Conclusion and Significance: This suggests that the cellular immune responses against HIV-1 in controller patients may be broader than we had previously anticipated.

Leukotriene B(4) amplifies NF-kappa B activation in mouse macrophages by reducing SOCS1 inhibition of MyD88 expression

Activation of NF-kappa B and 5-lipoxygenase-mediated (5-LO-mediated) biosynthesis of the lipid mediator leukotriene B(4) (LTB(4)) are pivotal components of host defense and inflammatory responses. However, the role of LTB(4) in mediating innate immune responses elicited by specific TLR ligands and cytokines is unknown. Here we have shown that responses dependent on MyD88 (an adaptor protein that mediates signaling through all of the known TLRs, except TLR3, as well as IL-1 beta and IL-18) are reduced in mice lacking either 5-LO or the LTB(4) receptor BTL1, and that macrophages from these mice are impaired in MyD88-dependent activation of NF-kappa B. This macrophage defect was associated with lower basal and inducible expression of MyD88 and reflected impaired activation of STAT1 and overexpression of the STAT1 inhibitor SOCS1. Expression of MyD88 and responsiveness to the TLR4 ligand LPS were decreased by Stat1 siRNA silencing in WT macrophages and restored by Socs1 siRNA in 5-LO-deficient macrophages. These results uncover a pivotal role in macrophages for the GPCR BLT1 in regulating activation of NF-kappa B through Stat1-dependent expression of MyD88.

Respiratory allergy to Blomia tropicalis: Immune response in four syngeneic mouse strains and assessment of a low allergen-dose, short-term experimental model

Background: The dust mite Blomia tropicalis is an important source of aeroallergens in tropical areas. Although a mouse model for B. tropicalis extract (BtE)-induced asthma has been described, no study comparing different mouse strains in this asthma model has been reported. The relevance and reproducibility of experimental animal models of allergy depends on the genetic background of the animal, the molecular composition of the allergen and the experimental protocol. Objectives: This work had two objectives. The first was to study the anti-B. tropicalis allergic responses in different mouse strains using a short-term model of respiratory allergy to BtE. This study included the comparison of the allergic responses elicited by BtE with those elicited by ovalbumin in mice of the strain that responded better to BtE sensitization. The second objective was to investigate whether the best responder mouse strain could be used in an experimental model of allergy employing relatively low BtE doses. Methods: Groups of mice of four different syngeneic strains were sensitized subcutaneously with 100 mu g of BtE on days 0 and 7 and challenged four times intranasally, at days 8, 10, 12, and 14, with 10 mu g of BtE. A/J mice, that were the best responders to BtE sensitization, were used to compare the B. tropicalis-specific asthma experimental model with the conventional experimental model of ovalbumin (OVA)-specific asthma. A/J mice were also sensitized with a lower dose of BtE. Results: Mice of all strains had lung inflammatory-cell infiltration and increased levels of anti-BtE IgE antibodies, but these responses were significantly more intense in A/J mice than in CBA/J, BALB/c or C57BL/6J mice. Immunization of A/J mice with BtE induced a more intense airway eosinophil influx, higher levels of total IgE, similar airway hyperreactivity to methacholine but less intense mucous production, and lower levels of specific IgE, IgG1 and IgG2 antibodies than sensitization with OVA. Finally, immunization with a relatively low BtE dose (10 mu g per subcutaneous injection per mouse) was able to sensitize A/J mice, which were the best responders to high-dose BtE immunization, for the development of allergy-associated immune and lung inflammatory responses. Conclusions: The described short-term model of BtE-induced allergic lung disease is reproducible in different syngeneic mouse strains, and mice of the A/J strain was the most responsive to it. In addition, it was shown that OVA and BtE induce quantitatively different immune responses in A/J mice and that the experimental model can be set up with low amounts of BtE.