SP-A self-agglutination assay. a) The figure shows a scheme of the SP-A self-agglutination-assay. 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 scheme attempts to illustrate the components of the reactants, but does not render how the molecules bind exactly. b) The microscope pictures with a magnification of 10 times were taken under a light microscope. Picture a shows an agglutinate while picture b illustrates beads without agglutination. c) The graph illustrates the SP-A dependency of the bead agglutination. The agglutinate size is plotted against the amount of serum containing SP-A which was incubated with the beads, anti-goat antibody and goat-anti-human antibody in a buffer with calcium ions. Two different sera were used (Black triangle, SP-A concentration 20 ng/ml, sample 2 and balck square, SP-A concentration 21 ng/ml, sample 1) in the experiments which were repeated three times. The final SP-A amount was in 0.6 μl serum about 16 pg.