Studies in both humans and rodents have suggested that CD8(+) T cells contribute to the development of airway hyperresponsiveness (AHR) and that leukotriene B4 (LTB4) is involved in the chemotaxis of effector CD8(+) T cells (T-EFF) to the lung by virtue of their expression of BLT1, the receptor for LTB4. In the present study, we used a mast cell-CD8-dependent model of AHR to further define the role of BLT1 in CD8(+) T cell-mediated AHR. C57BL/6(+/+) and CD8-deficient (CD8(-/-)) mice were passively sensitized with anti-OVA IgE and exposed to OVA via the airways. Following passive sensitization and allergen exposure, C57BL/6(+/+) mice developed altered airway function, whereas passively sensitized and allergen-exposed CD8(-/-) mice failed to do so. CD8(-/-) mice reconstituted with CD8(+) T-EFF developed AHR in response to challenge. In contrast, CD8(-/-) mice reconstituted with BLT1-deficient effector CD8(+) T cells did not develop AHR. The induction of increased airway responsiveness following transfer of CD8(+) TEFF or in wild-type mice could be blocked by administration of an LTB4 receptor antagonist confirming the role of BLT1 in CD8(+) T cell-mediated AHR. Together, these data define the important role for mast cells and the LTB4-BLT1 pathway in the development of CD8(+) T cell-mediated allergic responses in the lung.

Neural pathways help control airway caliber and responsiveness. Yet little is known of how neural control changes as a function of development. In rabbits, we found electrical field stimulation (EFS) of airway nerves led to more marked contractile responses in 2‐ vs. 13‐week‐old animals. This enhanced response to EFS may be due to prejunctional, junctional, and/or postjunctional neural mechanisms. We assessed these mechanisms in airways of 2‐ and 13‐week‐old rabbits. The contractile responses to methacholine did not differ in the groups, suggesting postjunctional neural events are not primarily responsible for differing responses to EFS. To address junctional events, acetylcholinesterase (AChE) was measured (spectrophotometry). AChE was elevated in 2‐week‐olds. However, this should lead to less and not greater responses. Prejunctionally, EFS‐induced acetylcholine (ACh) release was assessed by HPLC. Airways of 2‐week‐old rabbits released significantly more ACh than airways from mature rabbits. Choline acetyltransferase, a marker of cholinergic nerves, was not different between groups, suggesting that more ACh release in young rabbits was not due to increased nerve density. ACh release in the presence of polyarginine increased significantly in both groups, supporting the presence of functional muscarinic autoreceptors (M2) at both ages. Because substance P (SP) increases release of ACh, SP was measured by ELISA. This neuropeptide was significantly elevated in airways of younger rabbits. Nerve growth factor (NGF) increased SP and was also significantly increased in airways from younger rabbits. This work suggests that increases in EFS‐induced responsiveness in young rabbits are likely due to prejunctional events with enhanced release of ACh. Increases in NGF and SP early in life may contribute to this increased responsiveness. Pediatr Pulmonol. 2004; 38:97–106. © 2004 Wiley‐Liss, Inc.

In certain models of allergic airway disease, mast cells facilitate the development of inflammation and airway hyper-responsiveness (AHR). To define the role of the high affinity IgE receptor (FcεRI) in the development of AHR, mice with a disruption of the α subunit of the high affinity IgE receptor (FcεRI−/−) were exposed on 10 consecutive days to nebulized OVA. Forty-eight hours after the last nebulization, airway responsiveness was monitored by the contractile response of tracheal smooth muscle to electrical field stimulation (EFS). After the 10-day OVA challenge protocol, wild-type mice demonstrated increased responsiveness to EFS, whereas similarly challenged FcεRI−/− mice showed a low response to EFS, similar to nonexposed animals. Further, allergen-challenged FcεRI−/− mice showed less airway inflammation, goblet cell hyperplasia, and lower levels of IL-13 in lung homogenates compared with the controls. IL-13-deficient mice failed to develop an increased response to EFS or goblet cell hyperplasia after the 10-day OVA challenge. We transferred bone marrow-derived mast cells from wild-type mice to FcεRI−/− mice 1 day before initiating the challenge protocol. After the 10-day OVA challenge, recipient FcεRI−/− mice demonstrated EFS-induced responses similar to those of challenged wild-type mice. Transferred mast cells could be detected in tracheal preparations. These results show that FcεRI is important for the development of AHR after an aerosolized allergen sensitization protocol and that this effect is mediated through FcεRI on mast cells and production of IL-13 in the lung.

RATIONALE: Allergic asthma is a CD4 T helper type 2 (Th2) cell mediated disease characterized by airway eosinophilia, hyperresponsiveness, and mucous secretion.Previously, we have shown Signal transducer and activator of transcription factor (Star)6 controls Th2 cell recruitment into the lung in a murine adoptive transfer model of asthma.Since eosinophilactive chemokine production, in addition to antigen-specific Th2 cell trafficking, were reduced in Stat6 -/-recipients, in the present study, we examined the role of pulmonary parenchymal Star6 in regulating eosinophil recruitment irrespective of T cell accumulation.METHODS: To isolate the role of Stat6 in regulating eosinophil recruitment to the lung from its role in regulating Th2 cell trafficking into the lung, we developed a model of asthma in which in vitro-differentiated Stat6 +/+ antigen-specific CD4 Th2 cells were directly instilled into the airways of naive Stat6 § and Stat6 -/-mice followed by aerosol antigen challenge.RESULTS: We found a dramatic absence of eosinophilia in the airways of Stat6 -/-mice that received Stat6 +/+ antigen-specific Th2 cells and airway antigen challenge.CONCLUSIONS: Our findings suggest that Stat6 is essential not only for Th2 trafficking, but is required for eosinophil recruitment into the lung in allergic pulmonary inflammation.

Recurrent aspiration of cow's milk has been shown to alter neural control of airways in young rabbits (Gelfand et al., 1997 ). The purpose of this study was to define the mechanisms responsible for in vitro cholinergic hyperresponsiveness in this model. Beginning at 1 week of age, rabbits received either 0.5 mL/kg whole cow's milk or sterile saline intranasally while under light anesthesia. This was repeated each weekday for 2 weeks. At 8 weeks of age, rabbits were sacrificed. Portions of lungs underwent lavage with sterile saline. Tracheal smooth muscle (TSM) segments were also removed. Segments were assessed for acetylcholine (ACh) release by high‐performance liquid chromatography ( HPLC) with electrochemical detection or acetylcholinesterase (AChE) kinetic activity by spectrophotometry. Substance P (SP), a neuropeptide that can increase ACh release from nerves, was also assessed using an enzyme immunoassay to define the content in lavage and TSM segments. Immunohistochemistry for SP within airways was also assessed.

The effects of an anti-CD23 monoclonal antibody (B3B4) in CD23-deficient and CD23-overexpressing mice were compared in a murine model of allergic sensitization. After sensitization and challenge with OA, mice developed increased serum levels of OA-specific IgE and IgG(1) with airway eosinophilia and AHR when compared with nonsensitized animals, Anti-CD23 treatment was studied under two protocols: 10-d OA aerosol exposure and intraperitoneal sensitization followed by aerosol challenge. In both protocols anti-CD23 significantly reduced IgE and IgG(1) levels, abolished eosinophilia, and normalized AHR in BALB/c and wild-type CD23(+/+) mice but not in CD23(-/-) mice, These changes were associated with increases in IFN-gamma and decreases in IL-4 production, suggesting that CD23 binding may affect not only IgE production but also the Th1/Th2 imbalance during the development of allergic AHR. Absence of CD23 in gene-deficient mice significantly enhanced OA-specific IgE and IgG(1) levels, airway eosinophilia, and AHR when compared with CD23(+/+) wild-type littermates after sensitization and airway challenge. Sensitized and challenged CD23 transgenic mice also developed eosinophilic airway inflammation and methacholine hyperresponsiveness, However, the extent of AHR, BAL, and tissue eosinophilia in these animals showed a significant negative correlation with levels of CD23 expression on splenic T and B cells, demonstrating a limiting role of CD23 in the development of allergic AHR.

Cytokines play an important role in modulating inflammatory responses and, as a result, airway tone. IL-10 is a regulatory cytokine that has been suggested for treatment of asthma because of its immunosuppressive and anti-inflammatory properties. In contrast to these suggestions, we demonstrate in a model of allergic sensitization that mice deficient in IL-10 (IL-10-/-) develop a pulmonary inflammatory response but fail to exhibit airway hyperresponsiveness in both in vitro and in vivo assessments of lung function. Reconstitution of these deficient mice with the IL-10 gene fully restores development of airway hyperresponsiveness comparable to control mice. These results identify an important role of IL-10, downstream of the inflammatory cascade, in regulating the tone of the airways after allergic sensitization and challenge.

Allergic sensitization in asthma develops as a consequence of complex interactions between T cells and antigen-presenting cells. We have developed several in vivo models to study allergen-specific T cell and B cell function and their relevance to allergic airway hyperresponsiveness (AHR), focusing on the role of the costimulatory molecules CD80 and CD86. Treatment of mice with anti-CD86, but not anti-CD80, significantly inhibited increased serum levels of ovalbumin (OA)-specific IgE and IgG1, airway eosinophilia, and AHR both after 10 d of OA aerosol exposure (in the absence of adjuvant) and after intraperitoneal sensitization followed by repeated airway challenges. Inhibition of AHR was associated with decreased IL-4 and IL-5 levels in the BAL fluid of sensitized mice, suggesting impaired Th2 function in anti-CD86-treated animals. This effect was not seen when mice received treatment only before allergen challenge, indicating that anti-CD86 acts through inhibition of allergic sensitization and not simply by inhibiting the influx of inflammatory cells. These data suggest that the CD86 costimulatory ligand plays a major role in the development of allergic inflammation and AHR in allergen-challenged mice. Further, this study demonstrates that T-B cell interactions during allergic sensitization are amenable to therapeutic manipulation and that selective blockade of accessory signals can be an effective means for modulating distinct T cell functions.

The mechanisms underlying the development of airway hyperresponsiveness are not fully delineated. We addressed this question by studying the effects of passive sensitization with anti-OVA IgE on the development of altered airway responsiveness (AR) following local challenge with OVA in normal and athymic mice. Both normal and athymic BALB/c mice developed allergen-specific immediate cutaneous hypersensitivity after passive sensitization with anti-OVA IgE. In contrast, the combination of local challenge with allergen via the airways and passive sensitization triggered the development of airway hyperresponsiveness only in normal but not in athymic mice. Treatment of athymic mice with IL-5 significantly increased eosinophil accumulation in the lungs after local challenge with OVA; increased airway reactivity was only observed in athymic mice which received anti-OVA IgE, not an unrelated IgE, plus IL-5 treatment and airway challenge with OVA. These findings identify the requirement for allergen-specific IgE and IL-5 for the development of airway hyperresponsiveness following allergen challenge via the airways.