NHLBI workshop summaries. Neuroimmune interactions in the lung

Pathophysiological mechanisms of asthma. Application of cell and molecular biology techniques

Asthma is a common increasing and relapsing disease that is associated with genetic and environmental factors such as respiratory viruses and allergens. It causes significant morbidity and mortality. The changes occurring in the airways consist of a chronic eosinophilic and lymphocytic inflammation, together with epithelial and structural remodeling and proliferation, and altered matrix proteins, which underlie airway wall narrowing and bronchial hyperresponsiveness (BHR). Several inflammatory mediators released from inflammatory cells such as histamine and cysteinyl-leukotrienes induce bronchoconstriction, mucus production, plasma exudation, and BHR. Increased expression of T-helper 2 (Th2)-derived cytokines such as interleukin-4 and 5 (IL-4, 5) have been observed in the airway mucosa, and these may cause IgE production and terminal differentiation of eosinophils. Chemoattractant cytokines (chemokines) such as eotaxin may be responsible for the chemoattraction of eosinophils to the airways. The initiating events are unclear but may be genetically determined and may be linked to the development of a Th2-skewed allergen-specific immunological memory. The use of molecular biology techniques on tissues obtained from asthmatics is increasing our understanding of the pathophysiology of asthma. With the application of functional genomics and the ability to transfer or delete genes, important pathways underlying the cause if asthma will be unraveled. The important outcome of this is that new preventive and curative treatments may ensue.

Influence of beta-endorphin on the production of reactive oxygen and nitrogen intermediates by rabbit alveolar macrophages

1. Alveolar rabbit macrophages were studied for superoxide and nitric oxide production at basal levels and upon stimulation with phorbol myristate acetate (PMA), zymosan, cytokines (two types of interferon), and lipopolysaccharide in the presence (or absence) of beta-endorphin or hydroxylamine or both. 2. Beta-endorphin diminished (statistically significant at concentration of 10(-8) M) superoxide production by PMA-stimulated macrophages but augmented reactive oxygen generation (10(-12) M beta-endorphin) by zymosan-activated cells. 3. In the presence of hydroxylamine, beta-endorphin had a visible (albeit not statistically significant) suppressive effect on nitrite production by PMA-activated cells. 4. Cytokine-stimulated macrophages enhanced nitric oxide production in the presence of hydroxylamine and beta-endorphin in culture supernatants. 5. Beta-endorphin exerted different modulatory effects on the production of reactive oxygen and nitrite intermediates by rabbit alveolar macrophages (suppression or enhancement) that was strictly dependent on the method of cell activation.

In vitro and in vivo effects of tachykinins on immune cell function in guinea pig airways

The effects of sensory neuropeptides substance P (SP) and neurokinin A (NKA) on immune cell recruitment and macrophage activation were determined. Guinea pigs exposed to capsaicin aerosol exhibited eosinophil and neutrophil influx into their bronchoalveolar lavage (BAL) fluid 24 h after treatment; SP aerosol elicited eosinophil influx, whereas NKA aerosol exposure caused neutrophil recruitment. Inhalation of capsaicin, NKA or SP aerosols also enhanced superoxide production induced by zymosan in cultured alveolar macrophages. Incubation of alveolar macrophages with SP or NKA in culture for the same time (24 h) did not potentiate the response to zymosan. Hence, tachykinin-mediated airway effects may not be the result of direct actions on target cells but rather involve alternate mechanisms and mediators which do not necessarily reflect in vitro data.