RECONSTITUTION OF OPSONIZING ACTIVITY BY INFUSION OF MANNAN-BINDING LECTIN (MBL) TO MBL-DEFICIENT HUMANS

Mannan-binding lectin (MBL, previously named mannan-binding protein, M BP) is a serum collectin, which activates complement upon binding to m icrobial carbohydrates. This results in opsonization of the microorgan isms as well as direct complement-mediated killing. Clinical evidence indicates that MBL has an important role in the innate immune defence against various pathogens. Genetically determined MBL deficiency is as sociated with increased susceptibility to infections. We have infused two MEL-deficient individuals with clinical grade MEL, purified from p ooled donor plasma, in doses sufficient to attain normal concentration of MBL in serum. This resulted in normalization of complement-mediate d opsonization. An initial rapid decrease in the serum concentration o f MBL was followed by a slower decline with an estimated half-life of about 6 days. No adverse effects were observed and anti-MEL antibodies could not be detected following several MBL infusions. One of the two MBL recipient, a two-year-old girl, who had been suffering from repea ted infections from the age of 4 months, was given a total of six MBL infusions. She has subsequently remained healthy for more than three y ears.