Supplementary Material for: Collectin Kidney 1 Plays an Important Role in Innate Immunity against Streptococcus pneumoniae Infection

Collectins are C-type lectins that are involved in innate immunity as pattern recognition molecules. Recently, collectin kidney 1 (CL-K1) has been discovered, and in vitro studies have shown that CL-K1 binds to microbes and activates the lectin complement pathway. However, in vivo functions of CL-K1 against microbes have not been elucidated. To investigate the biological functions of CL-K1, we generated CL-K1 knockout (CL-K1-/-) mice and then performed a <i>Streptococcus pneumoniae</i> infection analysis. First, we found that recombinant human CL-K1 bound to <i>S. pneumoniae</i> in a calcium-dependent manner, and induced complement activation. CL-K1-/- mice sera formed less C3 deposition on <i>S. pneumoniae</i>. Furthermore, immunofluorescence analysis in the wild-type (WT) mice demonstrated that CL-K1 and C3 were localized on <i>S. pneumoniae</i> in infected lungs. CL-K1-/- mice revealed decreased phagocytosis of <i>S. pneumoniae</i>. Consequently, less <i>S. pneumoniae</i> clearance was observed in their lungs. CL-K1-/- mice showed severe pulmonary inflammation and weight loss in comparison with WT mice. Finally, the decreased clearance and severe pulmonary inflammation caused by<i> S. pneumoniae</i> infection might cause higher CL-K1-/- mice lethality. Our results suggest that CL-K1 might play an important role in host protection against <i>S. pneumoniae</i> infection through the activation of the lectin complement pathway.