Advances in the immunobiology of eosinophils and their role in disease

Oxidative stress and lung inflammation in airways disease

Oxidative stress results from an oxidant/antioxidant imbalance in favour of oxidants. A large number of studies have demonstrated that increased oxidative burden occurs in airways diseases, shown by increased marks of oxidative stress in the airspaces and systemically in these patients. There is now substantial evidence that oxidative stress plays an important role in the injurious and inflammatory responses in airways diseases such as asthma and chronic obstructive pulmonary disease (COPD). In addition to these proinflammatory mechanisms resulting from oxidative stress, protective mechanisms such as the upregulation of protective antioxidant genes also occur. At present, effective antioxidant therapy that has good bioavailability and potency is not available. Such drugs are being developed and should in the future allow the hypothesis that oxidative stress is a fundamental factor in the inflammation, which occurs in these airways diseases to be tested.

Rhinovirus infection up-regulates eotaxin and eotaxin-2 expression in bronchial epithelial cells

BACKGROUND

Human rhinoviruses (RVs) are the most common precipitants of asthma exacerbations. RV infection of bronchial epithelium results in local airway inflammation inducing eosinophil recruitment and activation. Induction of eosinophil chemoattractants could represent a central mechanism, as well as a prime target for intervention.

OBJECTIVE

To assess the effect of RV infection on mRNA expression and production of eosinophil chemoattractants by bronchial epithelial cells in-vitro.

METHODS

BEAS-2B cells were infected with major and minor RVs and the mRNA expression of IL-8, RANTES, MIP-1alpha, eotaxin, eotaxin-2, MCP-2, MCP-3 and MCP-4 was assessed by reverse transcription PCR. In cases where mRNA induction was observed, a fluoroimmunoassay was used to confirm protein production. To assess the virus-specificity of the observed reactions, cells were also exposed to inactivated RVs.

RESULTS

RV infection was able to up-regulate mRNA expression of IL-8, RANTES, MIP-1alpha, eotaxin and eotaxin-2, did not affect MCP-4, while MCP-2 and MCP-3 were not expressed either at baseline or after virus infection. Protein production was confirmed for IL-8, RANTES and eotaxin, but not for MIP-1alpha. When RVs were inactivated cytokine up-regulation was almost completely lost.

CONCLUSION

Infection of bronchial epithelial cells with RVs results in the production of a wide array of mediators that are able to chemoattract eosinophils. These include the eosinophil-specific molecules eotaxin and eotaxin-2, in addition to IL-8 and RANTES, which are the most abundant. Eosinophil recruitment after RV infection of bronchial epithelium could represent a central event in the pathogenesis of virus-induced asthma exacerbations.

New insights into the second generation antihistamines

Second generation antihistamines are recognised as being highly effective treatments for allergy-based disease and are among the most frequently prescribed and safest drugs in the world. However, consideration of the therapeutic index or the benefit/risk ratio of the H1 receptor antagonists is of paramount importance when prescribing this class of compounds as they are used to treat non-life threatening conditions. There are many second generation antihistamines available and at first examination these appear to be comparable in terms of safety and efficacy. However, the newer antihistamines in fact represent a heterogeneous group of compounds, having markedly differing chemical structures, adverse effects, half-life, tissue distribution and metabolism, spectrum of antihistaminic properties, and varying degrees of anti-inflammatory effects. With regard to the latter, there is growing awareness that some of these compounds might represent useful adjunct medications in asthma therapy. In terms of safety issues, the current second generation grouping includes compounds with proven cardiotoxic effects and others with the potential for adverse drug interactions. Moreover, some of the second generation H1 antagonists have given cause for concern regarding their potential to cause a degree of somnolence in some individuals. It can be argued, therefore, that the present second generation grouping is too large and indistinct since this was based primarily on the concept of separating the first generation sedating compounds from nonsedating H1 antagonists. Although it is too early to talk about a third generation grouping of antihistamines, future membership of such a classification could be based on a low volume of distribution coupled with a lack of sedating effects, drug interactions and cardiotoxicity.

Eosinophil granule proteins and their role in disease

The eosinophil has a potent armory of proinflammatory mediators with considerable potential to initiate and sustain an inflammatory response. These include cytotoxic granule proteins, cytokines, chemokines, and lipid mediators. Eosinophils are considered important in the immune response to infection with helminthic parasitic worms. Incrementally increasing evidence supports a critical role for their proinflammatory activities in diverse human conditions, most notably in allergic diseases such as asthma. In these conditions severe tissue damage is a consequence of an inappropriate accumulation of eosinophils and the subsequent release of their highly toxic granule proteins. In addition, release of granule-associated products such as chemokines and cytokines at the sites of inflammation is likely to have significant paracrine and autocrine relevance. This review will update recent developments in understanding the role that eosinophil granule proteins play in human disease, particularly those of the respiratory tract.