had bound each SP-D monomer. HD5 bound SP-D with similar
affinity to HNP 1–3, but evidently had fewer binding sites on a
SP-D molecule because its molar ratio was half that of the HNPs.
Two other human -defensins, HNP-4 and HD6, failed to bind
SP-D appreciably. Overall, the ELISA and SPR results were concordant
for HNP-1, HNP-2, and HNP-3. Both assays also agreed
that HBDs bound minimally, if at all, to SP-D.