Importance of basophils in eosinophilic asthma: the murine counterpart.

Several experimental studies in mice showed that basophils participate in the initiation of Th2 adaptive immune response, in addition to the effector phase. However, the role of basophils in allergic airway inflammation is less clear. The aim of this experiment was to assess the importance of basophils in recruiting inflammatory cells and, in particular, eosinophils in a murine model of asthma induced by Aspergillus fumigatus allergens. Additionally, bronchial reactivity was evaluated. Basophil depletion resulted in a reduction of inflammatory cells in the airways and eosinophil recruitment was significantly impaired. Also bronchial reactivity seemed to be impaired in basophil-depleted mice, but the result was not statistically significant. According to these preliminary data, basophils seem to influence the local eosinophilic response of allergic asthma.

IL-15-deficient mice develop enhanced allergic responses to airway allergen exposure.

BACKGROUND: Interleukin-15 is a pleiotropic cytokine that is critical for the development and survival of multiple haematopoietic lineages. Mice lacking IL-15 have selective defects in populations of several pro-allergic immune cells including natural killer (NK) cells, NKT cells, and memory CD8+ T cells. We therefore hypothesized that IL-15-/- mice will have reduced inflammatory responses during the development of allergic airway disease (AAD). OBJECTIVE: To determine whether IL-15-/- mice have attenuated allergic responses in a mouse model of AAD. METHODS: C57BL/6 wild-type (WT) and IL-15-/- mice were sensitized and challenged with ovalbumin (OVA), and the development of AAD was ascertained by examining changes in airway inflammatory responses, Th2 responses, and lung histopathology. RESULTS: Here, we report that IL-15-/- mice developed enhanced allergic responses in an OVA-induced model of AAD. In the absence of IL-15, OVA-challenged mice exhibited enhanced bronchial eosinophilic inflammation, elevated IL-13 production, and severe lung histopathology in comparison with WT mice. In addition, increased numbers of CD4+ T and B cells in the spleens and bronchoalveolar lavage (BAL) were also observed. Examination of OVA-challenged IL-15Rα-/- animals revealed a similar phenotype resulting in enhanced airway eosinophilia compared to WT mice. Adoptive transfer of splenic CD8+ T cells from OVA-sensitized WT mice suppressed the enhancement of eosinophilia in IL-15-/- animals to levels observed in WT mice, but had no further effects. CONCLUSION AND CLINICAL RELEVANCE: These data demonstrate that mice with an endogenous IL-15 deficiency are susceptible to the development of severe, enhanced Th2-mediated AAD, which can be regulated by CD8+ T cells. Furthermore, the development of disease as well as allergen-specific Th2 responses occurs despite deficiencies in several IL-15-dependent cell types including NK, NKT, and γδ T cells, suggesting that these cells or their subsets are dispensable for the induction of AAD in IL-15-deficient mice.

Basophils are rapidly mobilized following initial aeroallergen encounter in naïve mice and provide a priming source of IL-4 in adaptive immune responses.

Chronic aeroallergen inhalation elicits the expansion of IL-4-producing Th2 cells and the production of IgE antibodies. In sensitized subjects, who have established IgE and Th2 responses, re-exposure to allergen leads to rapid recruitment of basophils, which are thought to be important effectors of late phase allergic reactions. Several investigations of responses to parasites and injected antigens have identified an additional role for basophils as innate immune effectors during initial antigen encounter in immunologically naïve hosts. These cells constitutively express IL-4 and promote Th2 polarized adaptive responses to such antigens. Their early recruitment and modulation of cellular immune responses to natural inhaled allergens in the airways has been scarcely investigated. In this study, basophils were enumerated in lung tissue, blood and spleen from BALB/c mice in the first days after inhalation of an aqueous extract of the allergen, Aspergillus fumigatus (Af). Af inhalation induced rapid increases in basophil numbers in the lung, blood and spleen. This was Rag-1-, MyD88- and IL-3-independent. The basophils expressed abundant IL-4. Their depletion during Af sensitization resulted in an attenuated induction of both IL-4 producing Th lymphocytes and specific IgE and IgG1 responses to an inhaled protein antigen, ovalbumin, which was co-administered. Our results suggest that basophils are rapidly recruited to the airways of naïve mice following initial fungal allergen exposure, produce IL-4 and influence the development of the adaptive immune response.

Pro-inflammatory role of natural killer cells in the development of allergic airway disease.

BACKGROUND: Natural Killer (NK) cells have been implicated in the development of allergic airway inflammation. However, the in vivo role of NK cells has not been firmly established due to the lack of animal models with selective deficiencies in NK cells. OBJECTIVE: To determine the specific contribution of NK cells in a murine model of allergic airway disease (AAD). METHODS: The role of NK cells in AAD was studied using NK-deficient (NKD) mice, perforin(-/-) mice, and mice depleted of Ly49A/D/G(+) NK cell subsets in an ovalbumin-induced model of allergic airway disease (OVA-AAD). RESULTS: Induction of OVA-AAD in C57BL/6 wild-type (WT) mice resulted in the expansion of airway NK cells and the development of pronounced airway eosinophilia. In the absence of NK cells or specific subsets of NK cells, either in NKD mice, or after the depletion of Ly49A/D/G(+) NK cells, the development of OVA-AAD was significantly impaired as seen by decreased airway inflammation and eosinophilia, decreased secretion of the Th2 cytokines IL-4, IL-5 and IL-13 and diminished OVA-specific antibody production. Furthermore, while OVA-exposure induced a dramatic expansion of dendritic cells (DCs) in WT mice, their induction was significantly attenuated in NKD mice. Development of OVA-AAD in perforin(-/-) mice suggested that the proinflammatory role of NK cells is not dependent on perforin-mediated cytotoxicity. Lastly, induction of allergic disease by OVA-specific CD4 T cells from WT but not NK-depleted or NKD mice in RAG(-/-) recipients, demonstrates that NK cells are essential for T cell priming. CONCLUSIONS AND CLINICAL RELEVANCE: Our data demonstrate that conventional NK cells play an important and distinct role in the development of AAD. The presence of activated NK cells has been noted in patients with asthma. Understanding the mechanisms by which NK cells regulate allergic disease is therefore an important component of treatment approaches.

Immunoglobulin E antibodies enhance pulmonary inflammation induced by inhalation of a chemical hapten.

BACKGROUND: Occupational exposure to chemicals is an important cause of asthma. Recent studies indicate that IgE antibodies enhance sensitization to chemicals in the skin. OBJECTIVE: We investigated whether IgE might similarly promote the development of airway inflammation following inhalation of a contact sensitizer. METHODS: A model of chemical-induced asthma is described in which introduction of the low-molecular-weight compound, trinitrobenzene sulphonic acid (TNBS), via the respiratory tract was used for both sensitization and challenge. The role of IgE antibodies in the immune response to inhaled TNBS in this model was assessed by comparing the responses of wild-type (WT) and IgE-deficient (IgE(-/-)) mice on the BALB/c background. Reconstitution of circulating IgE levels by intravenous injection of IgE antibodies into IgE(-/-) mice before sensitization was performed to confirm the role of IgE in any differences observed between the responses of WT and IgE(-/-) mice. RESULTS: Intranasal challenge of TNBS-sensitized (but not sham-sensitized control mice) induced intense pulmonary inflammation. Macrophages, eosinophils and lymphocytes, including T, B, natural killer and natural killer T cells, were recruited to the airway and the animals displayed bronchial hyperresponsiveness (BHR) to methacholine. Serum levels of murine mast cell protease-1 (mMCP-1) were elevated suggesting mast cell activation. In contrast, the development of airway inflammation, recruitment of lymphocytes, induction of BHR and production of mMCP-1 were all significantly attenuated in IgE-deficient mice. Reconstitution of IgE(-/-) mice with IgE (of unrelated antigen specificity) before sensitization partially restored these features of asthma. CONCLUSION: Our data indicate that IgE antibodies non-specifically enhance the development of airway inflammation induced by exposure to chemical antigens.

Seasonal variations of virus abundance and viral control of the bacterial production in a backwater system of the danube river.

The abundance of virus-like particles in a backwater system of the Danube River covered a range of 1.2 x 10(sup7) to 6.1 x 10(sup7) ml(sup-1) from 1992 to 1993. Measurements of head diameters for these particles, all of which were presumed to be viruses, led to four defined size classes, ranging from <60 nm to >150 nm. The 60- to <90-nm size class contained the largest fraction of total particles (41%), followed by the 90- to <150-nm size class (33%). The frequency of size classes was not significantly different between the two years. The frequency of bacteria with mature phages ranged from 1 to 4% over the seasons, with mean burst sizes ranging from 17 to 36 phage per host cell. Among the bacterial morphotypes, rods and vibrios were the major host systems for phages, while coccoid and filamentous cells were considered negligible. Counts from transmission electron microscopy and acridine orange direct counts confirmed that rods and vibrios accounted for 85 to 95% of the bacterial population over the seasons. Virus decay experiments showed lower decay rates for temperatures between 5 and 15(deg)C (52 to 70% of the virus population remained) relative to 18 and 25(deg)C (31 to 51% of the virus remained). Bacterial production measurements, performed at the same time and under the same conditions as decay experiments, allowed us to estimate virus-induced death rates, which ranged from 15.8 to 30.1% over the year, with an average of 20% viral control of the bacterial production. Considering that mature phage particles are visible only in the last phase of the latent period and using a mean conversion factor of 5.4 from the literature, based on descriptions of various phage host systems to relate the percentage of visibly infected cells to the total percentage of the bacterial community that is phage infected, we estimate that some 5.4 to 21.6% of the bacterial population is infected with viruses. This would imply that virus-induced death rates of bacteria range from 10.8 to 43.2%. The data on virus-induced bacterial mortality obtained by both the viral decay method and the determination of the frequency of infected cells are compared and discussed.