Recent findings on the pathogenesis of bronchial asthma. Part II. The role of hormonal predisposition, environmental influences and conditioning leading to bronchial asthma

Asthmatic Augmentation of Airway Vagal Activity Involves Decreased Central Expression and Activity of CD73 in Rats

The severity of asthma is closely related to the intensity of airway vagal activity; however, it is unclear how airway vagal activity is centrally augmented in asthma. Here we report that in an asthma model of male Sprague-Dawley rats, the expression and activity of ecto-5'-nucleotidase (CD73) were decreased in airway vagal centers, ATP concentration in cerebral spinal fluid was increased, and the inhibitory and excitatory airway vagal responses to intracisternally injected ATP (5 μmol) and CD73 inhibitor AMPCP (5 μmol), respectively, were attenuated. In airway vagal preganglionic neurons (AVPNs) identified in medullary slices of neonatal Sprague-Dawley rats, AMPCP (100 μmol·L^-1) caused excitatory effects, as are shown in patch-clamp by depolarization, increased neuronal discharge, and facilitated spontaneous excitatory postsynaptic currents (sEPSCs). In contrast, exogenous ATP (100 μmol·L^-1, 1 mmol·L^-1) primarily caused inhibitory effects, which are similar to those induced by exogenous adenosine (100 μmol·L^-1). Adenosine A₁ receptor antagonist CPT (5 μmol·L^-1) blocked the inhibition of sEPSCs induced by 100 μmol·L^-1 exogenous ATP and that by 100 μmol·L^-1 exogenous adenosine, whereas 50 μmol·L^-1 CPT converted the inhibition of sEPSCs induced by 1 mmol·L^-1 ATP to facilitation that was blocked by addition of P2X receptor antagonist PPADS (20 μmol·L^-1). These results demonstrate that in rat, the sEPSCs of AVPNs are facilitated by extracellular ATP via activation of P2X receptors and inhibited by extracellular adenosine via activation of A₁ receptors; in experimental asthma, decreased CD73 expression and activity in airway vagal centers contribute to the augmentation of airway vagal activity through imbalanced ATP/ADO modulation of AVPNs.

The other T helper cells in asthma pathogenesis

The complex phenotype of allergic bronchial asthma involves a variable degree of bronchoobstruction, increased mucus production, and airway remodeling. So far it is suggested that it arises from multiple interactions of infiltrating and structural cells in the context of chronic airway inflammation that is orchestrated by T helper 2 (TH2) cells. By secreting a plethora of typical mediators such as interleukin (IL) 4, IL-5, and IL-13, these cells hold a key position in asthma pathogenesis. However, therapeutic approaches targeting these TH2-type mediators failed to improve asthma symptoms and impressively showed that asthma pathogenesis cannot be reduced by TH2 cell functions. Recently, other T helper cells, that is, TH9 and TH17 cells, have been identified and these cells also contribute to asthma pathogenesis, the processes leading to formation or aggravation of asthma. Furthermore, TH25 cells, TH3 cells, and regulatory T cells have also been implicated in asthma pathogenesis. This paper aims at summarizing recent insights about these new T helper cells in asthma pathogenesis.

Recent findings on the pathogenesis of bronchial asthma

In the first part of this series of papers (Székely and Pataki, 102) the pathogenesis of asthma was approached as a pathological antigen-antibody complex induced vago-vagal axon reflex. In the next part (103) the contribution of individual hormonal predisposition, the environmental and the most frequent allergizing factors have been reviewed. In the first section of this last (third) part of the review the genetic factors contributing to the asthma are surveyed. In this field a great progress has been made during the last decade, a lot of genes have been pinpointed which contribute to the heredity of the disease. In the second section of this last paper on the etiology of asthma an attempt is made to summarize the previously reviewed data and some new ones. Actually a new hypothesis is proposed that beyond the multitude of genetic, environmental and hormonal factors the underlying biochemical mechanism is simple: the disequilibrium of two functionally opposing second messenger systems in the airways: the Ca i ++ liberating PLC-PKC cascade and the Ca i ++ level reducing cAMP mediated one with preponderance of the former.