Agglutination of Pseudomonas aeruginosa by surfactant protein D

Surfactant protein D (SP-D) is part of the innate host defense system, and may bind and agglutinate invading microorganisms to enhance their removal. The ability of bronchoalveolar lavage (BAL) fluid to agglutinate bacteria and the relationship to its SP-D content are of interest and not yet known. A micromethod on slides was used to assess the agglutination of Pseudomonas aeruginosa by recombinant SP-D and native human BAL fluid. The SP-D-induced agglutination was blocked by calcium depletion, alkaline pH, or the presence of maltose. Twenty-three of 30 BAL fluids from outpatients carrying a chronic tracheostoma clearly agglutinated P. aeruginosa, which was completely inhibited by maltose. The extent of the agglutination correlated weakly to the concentration of SP-D in the BAL fluid, but not to that of SP-A. The functional property, i.e., the agglutination of P. aeruginosa by BAL fluid, was characterized and appeared related in part to the concentration of SP-D. Additional factors, such as the multimeric organization of SP-D, are likely to contribute to the agglutination of microorganisms by BAL or other body fluids. The assay presented will allow the systematic evaluation of small-volume samples for SP-D agglutinating ability from subjects with various lung diseases.