Dynamic changes in epidermal Ia-positive cells in allergic contact sensitivity reactions in mice

In mice sensitized with trinitrochlorobenzene, serial changes in epidermal Ia-positive cells were studied at various times after challenge. Until 3 days post-challenge, the Ia-positive cells consisted only of dendritic Langerhans cells; their number was decreased but they were significantly enlarged, with extending dendrites. Some Langerhans cells were also found surrounding a hair follicle, extending their dendrites toward the follicle like the spokes of a wheel. From 3 to 9 days after challenge, keratinocytes also began to express Ia antigens in the epidermis in addition to Langerhans cells, whose size diminished. This suggests that there are two phases in the response of the epidermal Ia antigens in contact sensitivity reactions, i.e. an early phase in which enlarged Langerhans cells are the only Ia-positive cells in the epidermis, and a late phase in which keratinocytes take over as the major Ia-positive cells, while Langerhans cells resume their original size. Ia antigen expression on keratinocytes in this late phase probably plays a crucial role in completely eliminating allergens deposited on the keratinocytes.

Prostaglandin F2 alpha increases responsiveness of pulmonary airways in dogs

We studied the effect of prostaglandin F2 alpha (PGF2 alpha) on the responsiveness of pulmonary airways in dogs. Airway responsiveness was assessed by determining the bronchoconstrictor response to increasing concentrations of acetylcholine aerosol delivered to the airways. In each of five dogs, we determined responsiveness during treatment with physiologic saline, histamine, or PGF2 alpha aerosols. The doses of histamine and PGF2 alpha were determined by establishing the largest dose of each which could be given to the dog without causing bronchoconstriction (subthreshold doses). We found that airway responsiveness was not significantly different during histamine treatment than after saline, however, responsiveness increased during treatment with PGF2 alpha. In addition, the hyperresponsiveness induced by PGF2 alpha was prevented by pretreatment with the ganglion blocking drug hexamethonium (5 mg/kg given intravenously). The results show that PGF2 alpha specifically increases the responsiveness of pulmonary airways in doses that do not cause bronchoconstriction, and suggest that the hyperresponsiveness involves a neural mechanism such as increased responsiveness of airway sensory nerves.

Indomethacin inhibits the airway hyperresponsiveness but not the neutrophil influx induced by ozone in dogs

To determine whether oxygenation products of arachidonic acid may be involved in the airway hyperresponsiveness induced by ozone exposure, we studied whether ozone-induced hyperresponsiveness could be inhibited by the prostaglandin synthetase inhibitor, indomethacin, in dogs. Airway responsiveness was assessed with dose-response curves of acetylcholine aerosol versus pulmonary resistance in 2 sets of experiments: in one set, 5 dogs were given no indomethacin treatment and were studied both before and after ozone exposure (3.0 ppm, 2 h); in another set, the same dogs were studied before indomethacin treatment or ozone exposure and then during treatment (1 mg/kg every 12 h for 4 days) both before and after ozone exposure. On each occasion, we also determined the number of neutrophils in biopsies of the airway epithelium. When the dogs were not treated with indomethacin, ozone caused a marked increase in responsiveness to acetylcholine and a marked increase in the number of neutrophils in the airway epithelium. When the dogs were given indomethacin, responsiveness was no different during treatment than before treatment, but more importantly, responsiveness did not increase significantly after they were exposed to ozone. Interestingly, indomethacin treatment did not affect either the baseline number of epithelial neutrophils before ozone exposure or the increase in the number of neutrophils after exposure. The results suggest that oxygenation products of arachidonic acid that are sensitive to inhibition by indomethacin play a role in ozone-induced hyperresponsiveness without affecting the influx of neutrophils.

Airway hyperresponsiveness and changes in cell counts in bronchoalveolar lavage after ozone exposure in dogs

We studied whether airway hyperresponsiveness induced by ozone exposure is associated with changes in the numbers of different types of cells in bronchoalveolar lavage in dogs. Airway responsiveness to acetylcholine and the numbers of cells in lavage fluid were determined 1 wk before and then 1 h and 1 wk after 2-h exposures to filtered air and to ozone (3.0 ppm) in each of 5 dogs. Airway responsiveness and the numbers of cells in lavage fluid did not change after exposure to filtered air. By contrast, airway responsiveness increased markedly 1 h after exposure to ozone and returned to control levels 1 wk later. In addition, the numbers of neutrophils and of ciliated epithelial cells in lavage increased markedly 1 h after ozone and returned to control levels 1 wk later. Our previous study showed that airway hyperresponsiveness induced by ozone is associated with an influx of neutrophils into the most central airways (1); the present results suggest that the hyperresponsiveness is also accompanied by an influx of neutrophils into more distal airways and by desquamation of airway epithelial cells.

Time course of airway hyperresponsiveness induced by ozone in dogs

To better understand the mechanism of ozone-induced airway hyperresponsiveness we determined the time course of the ozone effect in dogs. To do this we assessed airway responsiveness before ozone exposure and then at 1 h, 1 day, and 1 wk after ozone exposure. To assess responsiveness we anesthetized the dogs and obtained dose-response curves of increasing concentrations of acetylcholine or histamine aerosols delivered to the airways vs. pulmonary resistance. Ozone exposures were carried out with the dogs awake and at rest in an exposure chamber for 2 h breathing either through the nose and mouth at a level of 2.2 ppm or through a tracheostomy at a level of 1.0 ppm. For both acetylcholine and histamine and for both routes of ozone delivery airway responsiveness increased most markedly at 1 h after ozone, increased to a lesser degree 1 day later, and returned to control levels by 1 wk. The results are similar to our previous studies in humans that showed that ozone-induced hyperresponsiveness occurs shortly after exposure and is rapidly reversible and suggest that the ozone effect is linked to an acute inflammatory response in the airways.

Selective generation of leukotriene B4 by tracheal epithelial cells from dogs

The incubation of suspensions of canine tracheal epithelial cells of greater than 95% purity with arachidonic acid (25-200 micrograms/ml) for 60-120 min resulted in the generation of a maximum of 36.2 +/- 9.1 picomoles of leukotriene B4/10(6) cells, less than 2.0 picomoles of leukotrienes C4, D4, and E4/10(6) cells, and 1030 +/- 463, 767 +/- 500, and 324 +/- 100 picomoles/10(6) cells of 15-, 12-, and 5-hydroxy-eicosatetraenoic acids, respectively (mean +/- SEM, n = 8). The identity of leukotriene B4 was established by chromatographic and spectral properties, by reactivity with mono-specific anti-plasma, and by the chemotactic activity for neutrophils. Thus, the epithelium may be an important source of mediators of inflammation and hypersensitivity of pulmonary airways.

Importance of airway inflammation for hyperresponsiveness induced by ozone

We studied whether ozone-induced airway hyperresponsiveness correlates with the development of airway inflammation in dogs. To assess airway responsiveness, we determined increases in pulmonary resistance produced by delivering acetylcholine aerosol to the airways. To assess airway inflammation, we biopsied the airway mucosa and counted the number of neutrophils present in the epithelium. Airway responsiveness and inflammation were assessed in anesthetized dogs before ozone exposure and then 1 h and 1 wk after ozone (2.1 ppm, 2 h). Airway responsiveness increased markedly at 1 h after ozone and returned to control levels 1 wk later in each of 6 dogs, but it did not change after ozone in another 4 dogs. Furthermore, dogs that became hyperresponsive also developed a marked and reversible increase in the number of neutrophils in the epithelium, whereas dogs that did not become hyperresponsive had no change in the number of neutrophils. For the group of dogs, the level of airway responsiveness before and after ozone exposure correlated closely with the number of epithelial neutrophils. The results suggest that ozone-induced airway hyperresponsiveness may depend on the development of an acute inflammatory response in the airways.

A possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity

To investigate a possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity, we measured changes in RL and CL caused by electrical stimulation of cervical vagus nerve during the infusion of 5-HT, after treatment with atropine and propranolol in 18 cats. RL decreased to 56 +/- 3% (mean +/- SE) and CL increased to 186 +/- 13% of the prestimulated values, respectively, after stimulation. Hexamethonium diminished these responses significantly. Airway reactivity to 5-HT was reduced by continuous electrical stimulation of cervical vagus nerve in cats pretreated with atropine and propranolol. Hexamethonium potentiated airway reactivity to 5-HT. These results suggest that a nonadrenergic inhibitory nervous system could play an important role in the control of the bronchomotor tone and contribute to airway hyperreactivity.

The potential beneficial effect of a thromboxane synthetase inhibitor, OKY-1581, on increased lung vascular permeability in experimental pulmonary microembolization in dogs

To evaluate the potential beneficial effect of a thromboxane synthetase inhibitor, OKY-1581, on increased pulmonary vascular permeability in pulmonary microembolization, we have measured the filtration coefficient in the nonembolized lung after unilateral microembolization in dogs. The unilateral microembolization caused marked elevations in pulmonary artery pressure and blood flow to the nonembolized lung, while pulmonary venous pressure in nonembolized lung did not change. The pulmonary vascular resistance in nonembolized lung did not increase significantly. The filtration coefficient (kf) in nonembolized lung increased to 0.14 +/- 0.02 from te base line value of 0.07 +/- 0.01 ml/min/mmHg/100 g at 30 min after microembolization when the initial hemodynamic changes reduced toward the base line value. In OKY-1581 treated dogs, similar hemodynamic changes did not result in the filtration coefficient in nonembolized lung. Platelet aggregagation was also inhibited after microembolization in OKY-1581 treated dogs. Based on these results, we could conclude that OKY-1581 will serve as a potent beneficial protective drug against pulmonary edema by inhibiting the release of thromboxane A2 following microembolization in the pulmonary vascular bed.