Kinetic retrieval of eosinophil cationic protein, hyaluronan, secretory IgA, albumin, and urea during BAL in healthy subjects

Determination of absolute concentrations of various soluble components of the epithelial lining fluid (ELF) may be valuable to estimate inflammatory activities within the underlying lung tissue. Internal standards may then be used as markers of dilution of bronchoalveolar lavage (BAL). The aim of this study was to determine whether different dwell times would affect the relationship between the concentrations of any of the three potential internal standards (secretory IgA [SIgA], albumin, and urea), and the concentrations of two potential markers of inflammation (eosinophil cationic protein [ECP] and hyaluronan [HA]) in BAL. A series of aliquots of BAL fluid were aspirated every 60 s up to 8 min after a bolus instillation of saline solution in 20 healthy subjects (10 smokers). The BAL concentrations of albumin and urea increased with time, consistent with continuous diffusion from the body water pool, absorption of the BAL fluid, or both. The rate constant of diffusion was 1,000 times higher for urea than for albumin (3.38 x 10(-1) and 3.64 x 10(-4), respectively), reflecting the difference in molecular weights, and in agreement with the notion that albumin and urea appeared in BAL fluid by a rate-limited procedure related to osmotic transfer. Biexponential increases of SIgA were recorded, suggesting a two-compartmental origin of this compound, normally located to mucosal membranes and presumed to be dissolved in ELF. Time-dependent increases in BAL fluid of HA also were recorded, but on the other hand, the ECP concentrations tended to level off after an initial increase, suggesting that the bulk of ECP appeared in BAL by a nonosmotic mechanism. We conclude that the kinetics of these three internal standards in BAL fluid differs greatly from each other and from the kinetics of the two selected markers of inflammation. Consequently, internal standards for determination of absolute concentrations of markers of inflammation in ELF should be carefully selected because of the requirement of matched kinetics of the markers.