Interaction of fungal spores with the lungs: Distribution and retention ofinhaled puffball (Calvatia excipuliformis) spores

Background: The biologic responses to inhaled airborne fungal spores, which are well-known allergen carriers, would be better understood if we had an insight into their pattern of distribution and interaction with lung struct ures. Objectives: To investigate the retention characteristics of inhaled basidio spores, which often represent the major portion of the spore load in air-sa mpling surveys and to analyze their regional distribution within and intera ction with the lungs. Methods: Intubated and anesthetized Syrian Golden hamsters inhaled aerosols of puffball (Calvatia excipuliformis) spores, with an aerodynamic diameter of 3.1 mu m, either by spontaneous breathing (group A, n = 3) or by contin uous negative-pressure ventilation (group B, n = 4). Lungs were fixed by in travascular perfusion of fixative solution within 29 minutes of the initial inhalation, and tissue samples were then professed for light and electron microscopy, Results: Stereological (fractionator) analysis of lung tissue revealed that the greatest number of spores was deposited within the alveoli (67.2% in g roup A and 89.8% in group B), The intrapulmonary conducting airways retaine d an intermediate proportion (32.3% in group A and 10.0% in group B), where as the extrapulmonary mainstem bronchi and trachea held the lowest proporti on (0.5% or less). Deposited spores were lodged within the aqueous lining l ayer and in close proximity to the epithelial cells. Within the intrapulmon ary conducting airways, 22.3% of the spores in group A and 9.0% of those in group B had been engulfed by macrophages. Conclusion: This study demonstrates that inhaled 3-mu m-diameter basidiospo res become distributed over a large surface area. It also reveals that such particles are displaced by surfactant (surface forces) into the aqueous li ning layer of airways and alveoli, thereby facilitating subsequent phagocyt osis by macrophages. This interaction of spores with lung structures may be important for the development of respiratory allergies induced by airborne fungal allergens.