Kinetic analysis of respiratory tract proteins recovered during a sequential lavage protocol

Although bronchoalveolar lavage (BAL) has been used as a research tool for over a decade, the technique of lavage has varied markedly between laboratories. For example, lavage instillate volumes from 50 to 300 ml have been used, and yet the influence of the variable of total lavage volume on subsequent protein recovery is uncertain. We performed sequential BAL (50 ml/aliquot; total volume, 300 ml) of the right middle lobe of 14 normal volunteers and separately processed and analyzed recovered aliquots for the absolute and relative concentrations of several protein substances. These proteins include free secretory component and secretory IgA, which emanate from airway secretions, and IgG, which is thought to transude from more distal alveolar sites. Analysis of these data showed a marked decrease in the absolute concentration of all proteins measured in serial aliquots. Analysis of protein ratios in sequential aliquots, however, revealed no significant change from the first to the fifth recovered aliquot. Finally, we analyzed the influence of the size of the first recovered aliquot on absolute and relative concentrations of proteins. Here there seemed to be a trend indicating preferential recovery of airway proteins in smaller aliquots. This was significant for the ratio of free secretory component to albumin (p less than 0.05). We conclude that lung proteins are efficiently and homogeneously sampled with 100 ml of lavage instillate. Larger volumes will add more protein but not alter protein ratios. Lavage with smaller volumes may preferentially sample airway proteins.