SP-A self-agglutination and fractions. The graphs show the self-agglutination ability (y-axis) of different SP-A structures derived from BAL (b) and serum (a) (x-axis) of the study populations. The streptavidin beads were coupled to biotinylated rabbit anti-goat antibodies which bound goat anti-human SP-A antibodies. These anti-SP-A antibodies bound SP-A at its N-terminal end, so SP-A could self-agglutinate by its CRD. The SP-A amount was adjusted to 1 ng (final concentration 100 ng/ml). All experiments were analyzed by One way ANOVA. * stands for p < 0.05, ** for p < 0.01 and *** for p < 0.001. In BAL and serum of all three study populations (10 CF, 10 Bro, 7 C) there was a significant difference between the self-agglutination ability of the different structures (F10, F15 and F20). The octadecamers or more complex structures showed the best self-agglutination ability followed by the hexameric structures and then the dimers/trimers. Comparing the self-agglutination ability between the study groups, in all BAL fractions the SP-A oligomers derived from controls agglutinated significantly better than the SP-A oligomers derived from patients, while SP-A from bronchitis patients agglutinated still better than from CF patients; except for F20 of bronchitis samples, which showed the same self-agglutination ability as controls. In contrast to BAL in serum there was no difference between the study populations regarding the self-agglutination ability of the different fractions (p > 0.05). Comparing the agglutination ability between BAL and serum, only in the patient populations (CF and Bro) all SP-A structures derived from serum fractions agglutinated significantly better than the corresponding structures derived from BAL. While in CF patients this difference was highly significant for all structures in the bronchitis study population the significance decreased from fraction 10 over fraction 15 to fraction 20.