New concepts in the pathogenesis of asthma

Pathological changes according to the severity of asthma

BACKGROUND

There have been many studies concerning pathological changes in bronchial mucosa from asthmatics; however, few studies has been carried out to evaluate pathological changes according to the severity of asthma.

OBJECTIVE

This study was designed to evaluate the cellular components in bronchoalveolar lavage fluid (BALF) and histological abnormalities in asthmatics according to the severity of asthma.

METHODS

Bronchoalveolar lavages, bronchoscopic biopsies and ultrastructural examinations were performed in 13 asthmatics and 11 (BAL) or four (biopsies) non-asthmatic controls. The proportions of epithelial cells and correlations with PC20Meth which reflects bronchial hyperresponsiveness. Light microscopic examination revealed loss of epithelium, inflammatory cell infiltrations and thickening of the basement membrane which also showed significant correlation with PC20Meth. Hypertrophy of airway smooth muscles and hyperplasia of mucous glands were prominent in asthmatics but there was no difference according to the severity of asthma. Ultrastructural examination revealed that basement membrane thickening on light microscopic examination is due to the increased subepithelial collagen deposition with normal thickness of basal lamina.

CONCLUSION

These data suggest that loss of epithelial cells, infiltration of inflammatory cells, especially eosinophils, and increased deposition of subepithelial collagen play major roles in determining the severity of asthma and non-specific bronchial hyperresponsiveness.

Allergenicity of cow milk proteins

The allergenicity and antigenicity of cow milk proteins are age dependent. Because the nonspecific and specific factors inhibiting the passage of cow milk proteins through the epithelial layer of the intestine are deficient at birth, although developing during early infancy, allergy to cow milk may be acquired during the first year of life. Allergic reactivity to cow milk is lost during childhood in the vast majority of cases. This change may depend at least partly on the development of the local immune system of the gut producing antigen-specific IgA antibodies. Circulating IgG antibodies to cow milk proteins are always produced when an infant has cow milk in the diet but are not associated with allergy; their titer is reduced with age. Clinical challenge tests show that most cow milk-allergic patients react to several protein fractions of cow milk. A patient may have IgE antibodies to several fractions of cow milk, measured either by skin testing or by radioallergosorbent test. Likewise, various tests for cell-mediated immunity may show positive reactions to several fractions. No single major allergen is apparent in cow milk, according to either the challenge tests or laboratory procedures: casein, alpha-lactalbumin, and beta-lactoglobulin all show a high proportion of positive reactions.