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The effect of human eosinophil granule major basic protein on airway responsiveness in the rat in vivo. A comparison
D A Uchida1, S J Ackerman, A J Coyle
1Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado.
Abstract:
Major basic protein (MBP) is a highly cationic protein found in the granules of eosinophils. It has been postulated that MBP may participate in the pathogenesis of airway hyperresponsiveness exhibited by asthmatic patients. Accordingly, we used a rat model to investigate the effect of human MBP instillation on airway responsiveness and the possible role of cationic charge in the determination of this effect. Dose-response characteristics to inhaled methacholine (MDRC) were determined at baseline, and the animals were allowed to recover. Then animals in the experimental group received 100 micrograms of purified human MBP via direct instillation into the trachea. One hour after instillation, the MDRC were again assessed. Control animals received (in lieu of MBP) buffer from the void volume pool of the same chromatography column used to purify the MBP. One hour after instillation of MBP there was a significant increase in airway responsiveness to inhaled methacholine, whereas control animals exhibited no increase in airway responsiveness. Some animals from the MBP group were restudied 48 h after MBP instillation, by which time airway responsiveness had returned to baseline level. The effect of the polycations poly-L-arginine and poly-L-lysine on airway responsiveness was also examined. As with MBP, airway responsiveness to inhaled methacholine increased 1 h after the instillation of either polycation. In addition, acetylation of the charged groups on poly-L-lysine resulted in a loss of this effect. Histologic examination of the airways failed to reveal airway epithelial shedding 1 h after MBP or polycation instillation.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Major basic protein (MBP) instillation significantly increased airway hyperresponsiveness in rats, an effect also seen with other polycations, suggesting cationic charge plays a role in asthma pathogenesis.
Area of Science:
- Pulmonary Medicine
- Immunology
- Biochemistry
Background:
- Eosinophils contain Major Basic Protein (MBP), a highly cationic protein.
- MBP is implicated in the pathogenesis of airway hyperresponsiveness in asthma.
Purpose of the Study:
- To investigate the effect of human MBP instillation on airway responsiveness in a rat model.
- To determine the role of cationic charge in MBP-induced airway hyperresponsiveness.
Main Methods:
- Rats were instilled with purified human MBP or control buffer.
- Dose-response to inhaled methacholine was assessed before and 1 hour after instillation.
- The effects of poly-L-arginine and poly-L-lysine were also examined.
Main Results:
- MBP instillation significantly increased airway responsiveness to methacholine 1 hour post-instillation.
- Control animals showed no change in airway responsiveness.
- Poly-L-arginine and poly-L-lysine also increased airway responsiveness, which was lost upon acetylation of charged groups.
Conclusions:
- The cationic charge of MBP contributes to increased airway responsiveness.
- MBP and other polycations may play a role in asthma-related airway hyperresponsiveness.
- Airway epithelial shedding was not observed after MBP or polycation instillation.