Assessment of Surfactant Protein A (SP-A) dependent agglutination

Background: Monomers of the collectin surfactant associated
protein-A (SP-A) are arranged in trimers and higher oligomers. The
state of oligomerization differs between individuals and likely
affects SP-A's functional properties. SP-A can form aggregates
together with other SP-A molecules. Here we report and assess a
test system for the aggregate forming properties of SP-A in serum
and broncho-alveolar lavage samples. Methods: Anti-SP-A antibodies
fixed to latex beads bound SP-A at its N-terminal end and allowed
the interaction with other SP-A molecules in a given sample by
their C-terminal carbohydrate recognition domain (CRD) to
agglutinate the beads to aggregates, which were quantified by light
microscopy. Results: SP-A aggregation was dependent on its
concentration, the presence of calcium, and was dose-dependently
inhibited by mannose. Unaffected by the presence of SP-D no
aggregation was observed in absence of SP-A. The more complex the
oligomeric structure of SP-A present in a particular sample, the
better was its capability to induce aggregation at a given total
concentration of SP-A. SP-A in serum agglutinated independently of
the pulmonary disease; in contrast SP-A in lung lavage fluid was
clearly inferior in patients with chronic bronchitis and
particularly with cystic fibrosis compared to controls.
Conclusions: The functional status of SP-A with respect to its
aggregating properties in serum and lavage samples can be easily
assessed. SP-A in lung lavage fluid in patients with severe
neutrophilic bronchitis was inferior.