Abstract: Objective To investigate the effects of mannan-binding lectin (MBL) on the functions of human polymorphonuclear
cells (PMNs). Methods ELISA and Dot blot were performed to examine the binding between MBL and the microorganisms.
Flow cytometry and fluorescence microscopy were employed to analyze the phagocytosis of FITC-labeled microognisms by
the PMNs. Real-time quantitative PCR was used to detect the expression levels of IL-1β, TNF-α and CD11b mRNA in the
PMNs, and ELISA used to detect the levels of TNF-α and IL-6 in the supernatants of PMN culture. Nitro-blue tetrazolium
reduction assay was used to estimate the levels of superoxide production. Results MBL bound to the microorganisms in a
dose-dependent manner. MBL had no significant effect on phagocytosis of C. albicans and E.coli by the PMNs in the absence of
human serum, but in presence of mixed MBL-deficient human sera, MBL promoted the phagocytosis of C. albicans, which
could be blocked by mannan. Mannan treatment increased the expressions of IL-1β, TNF-α, IL-6 and CD11b and enhanced
superoxide production in the PMNs. Conclusion MBL can promote phagocytosis of microorganisms by PMNs and increase
the expressions of proinflamatory cytokines from PMNs in a complement lectin pathway-dependent manner.