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Loss of size‐selectivity at histamine‐induced exudation of plasma proteins in atopic nasal airways

Plasma proteins occur in the airway lumen in inflammatory airway diseases. This study tests the hypothesis that airway microvascular‐epithelial exudation of plasma proteins, as induced by a non‐injurious inflammatory mediator, is characterized by loss of size‐selectivity. Using a nasal pool‐device, the nasal mucosa of 10 allergic individuals, without current disease, was sequentially exposed to saline and histamine (40 and 400 μg ml–1). Nasal lavage fluid and blood‐levels of albumin (69 kD) and α2‐macroglobulin (720 kD) were determined. Histamine produced concentration‐dependent exudation of albumin and α2‐macroglobulin. The albumin/α2‐macroglobulin concentration ratio of the saline lavage fluid (baseline) was 40 ± 19. However, at the histamine challenges the ratios were 25 ± 3 and 22 ± 2, respectively, which did not differ from that of circulating plasma (22 ± 2). We conclude that there is minor and size‐selective luminal entry of plasma proteins at baseline. However, at concentration‐dependent exudative responses to histamine, plasma proteins enter the airway lumen without being sieved. These data indicate that inflammatory stimulus‐induced extravasation, lamina propria distribution and paracellular epithelial passage of plasma occur with minimal size‐selectivity. Inferentially, the full immunological capacity of plasma proteins may readily be made available at the surface of human intact airway mucosa.