Antigen induced modulation of autonomic nervous system responses in immunoglobulin-E - sensitized rabbit lung.

Abstract

The major objective of this project was to examine the potential for mediators of IgE-mediated allergic reactions to alter neural activity. The project was divided into three parts. In Part I, the ability of endogenously released chemical mediators to alter neural activity in vitro was assessed by measuring isometric contractile responses to electrical field stimulation (EFS) (2-128 Hz, 20 V, 0.5 msec. duration) of sensitized rabbit bronchi before and after exposure to the antigen horseradish peroxidase (HRP). Antigen enhanced bronchial responses to EFS with low frequencies: mean log (± S.E.) frequency which produced 20% of maximum response decreased from 1.04 (± 0.05) to 0.90 (± 0.07) Hz (p < 0.05). Responses of unsensitized bronchi were not enhanced by antigen. Chlorpheniramine, an H₁ antagonist, abolished the antigen effect. Antigen did not enhance the responses to exogenous acetylcholine. Hence, the antigen is apparently modulating neural activity and not smooth muscle per se. In Part II, the capacity for histamine to modulate vagally-induced bronchoconstriction in anesthetized, vagotomized, mechanically-ventilated rabbits was examined in vivo. Changes in pulmonary resistance induced by electrically stimulating the cut ends of the vagi (2-32 Hz, 20 V, 0.5 msec. duration) were assessed before and 10 minutes after histamine aerosolization (10 breaths of 10 mg/ml). Histamine inhalation potentiated vagally-induced bronchoconstriction at low frequencies: mean log (± S.E.) frequency producing a 20% change in pulmonary resistance decreased from 0.88 (± 0.09) to 0.56 (± 0.15) (p < 0.05). Chlorpheniramine abolished this effect. In Part III, the dependence on IgE antibodies of the in vitro modulation of neurally-induced contraction of sensitized bronchi was investigated. Rabbits were passively immunized with fractions enriched with HRP-specific IgE, IgG, or IgM antibodies. After 72 hours, rabbits were sacrificed and the responses of bronchi to EFS were assessed before and after antigen challenge. Antigen enhanced the responses to EFS only of bronchi passively sensitized with IgE. Therefore, antigen enhancement of neural activity was dependent on IgE. These studies demonstrate that the interaction between antigen and IgE antibodies can induce the release of chemical mediators which can alter neural activity.