A human lectin array has been developed to probe the interactions of innate immune receptors
with pathogenic and commensal micro-organisms. Following the successful introduction of a
lectin array containing all of the cow C-type carbohydrate-recognition domains (CRDs), a
human array described here contains the C-type CRDs as well as CRDs from other classes
of sugar-binding receptors, including galectins, siglecs, R-type CRDs, ficolins, intelectins and
chitinase-like lectins. The array is constructed with CRDs modified with single-site biotin tags,
ensuring that the sugar-binding sites in CRDs are displayed on a streptavidin-coated surface
in a defined orientation and are accessible to the surfaces of microbes. A common approach
used for expression and display of CRDs from all of the different structural categories of
glycan-binding receptors allows comparisons across lectin families. In addition to previously
documented protocols for binding of fluorescently-labeled bacteria, methods have been
developed for detecting unlabeled bacteria bound to the array by counter-staining with DNA binding dye. Screening has also been undertaken with viral glycoproteins and bacterial and
fungal polysaccharides. The array provides an unbiased screen for sugar ligands that interact
with receptors and many show binding not anticipated from earlier studies. For example, some
of the galectins bind with high affinity to bacterial glycans that lack lactose or N acetyllactosamine. The results demonstrate the utility of the human lectin array for providing
a unique overview of the interactions of multiple classes of glycan-binding proteins in the
innate immune system with different types of micro-organisms.