Mannose-binding lectin (MBL) is an important serum protein that functions in the innate immune system and has been considered to have therapeutic potential in MBL replacement therapies for patients with deficient or low levels of MBL. In this study, we established a Chinese hamster ovary (CHO) cell line that overexpresses the recombinant human MBL (rhMBL) protein. In an 11-day batch culture process using a 30-L bioreactor (20-L working volume) and serum-free medium, these cells could produce over 226 mg/L of rhMBL protein. The recombinant protein was then purified to homogeneity from the culture supernatant using a three-step chromatographic procedure that resulted in a recovery rate of approximately 55%. This purified rhMBL protein adopted oligomeric bouquet-like structures that were similar to those of native MBL present in human blood, and these oligomeric structures were reported to be critical in MBL functions. We further demonstrated in carbohydrate binding and complementation activation assays that this rhMBL protein was functionally active with very similar dissociation constants and half maximal effective concentrations to those of native MBL. (c) 2012 Elsevier Inc. All rights reserved.