Human Intelectin-1 Promotes Cellular Attachment and Neutrophil Killing of Streptococcus pneumoniae in a Serotype-Dependent Manner.

Human intelectin-1 (hIntL-1) is a secreted glycoprotein capable of binding exocyclic 1,2-diols within surface glycans of human pathogens such as Streptococcus pneumoniae, Vibrio cholerae, and Helicobacter pylori. For the latter, lectin binding was shown to cause bacterial agglutination and increased phagocytosis, suggesting a role for hIntL-1 in pathogen surveillance. In this study, we investigated the interactions between hIntL-1 and S. pneumoniae, the leading cause of bacterial pneumonia. We show that hIntL-1 also agglutinates S. pneumoniae serotype 43, which displays an exocyclic 1,2-diol moiety in its capsular polysaccharide but is unable to kill in a complement-dependent manner or to promote bacterial killing by peripheral blood mononuclear cells. In contrast, hIntL-1 not only significantly increases serotype-specific S. pneumoniae killing by neutrophils but also enhances the attachment of these bacteria to A549 lung epithelial cells. Taken together, our results suggest that hIntL-1 participates in host surveillance through microbe sequestration and enhanced targeting to neutrophils.