Plasma-derived mannose-binding lectin shows a direct interaction with C1-inhibitor

• Published in: Molecular immunology Vol. 58; no. 2; pp. 187 - 193
• Main Authors: Keizer, Mischa P., Kamp, Angela M., Brouwer, Nannette, van de Wetering, Marianne D., Wouters, Diana, Kuijpers, Taco W.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2014
• Subjects: Blood Proteins - metabolism; C1-inhibitor; Child; Complement C1 Inhibitor Protein - metabolism; Complement C4 - metabolism; Enzyme-Linked Immunosorbent Assay; Functionality; Humans; Mannose-Binding Lectins - deficiency; Mannose-Binding Lectins - metabolism; Mannose-Binding Protein-Associated Serine Proteases - metabolism; MBL-substitution; Multiprotein Complexes - metabolism; Plasma-derived MBL; Pre-activated MASPs; Protein Binding; Titrimetry; C1-inhibitor; MMC; rhMASP-2; LP; Mass-Spec; TMB; CP; AP; pAb; Functionality; MBL; Pre-activated MASPs; polyHRP; rhMBL; C1-inh; MASPs; pdMBL; Plasma-derived MBL; HPE; TP; MBL-substitution; mass-spectrometry; terminal pathway; MBL associated serine proteases; MBL/MASP/C1-inh; recombinant human MBL; lectin pathway; alternative pathway; classical pathway; mannan binding lectin; tetramethylbenzidine; polyclonal antibodies; recombinant human MASP-2; polymerized Horseradish peroxidase; high performance ELISA buffer
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2013.11.022

•The use of plasma-derived MBL is limited due to the presence of preactivated MASPs.•Activated MBL/MASP complexes rapidly form an interaction with serum inhibitor C1-inh.•MASP-depleted pdMBL or rhMBL may be valid alternatives to restore MBL-deficiency. MBL-deficiency has been associated with an increased frequency and severity of infection, in particular in children and under immunocompromized conditions. In an open uncontrolled safety and pharmacokinetic MBL-substitution study using plasma-derived MBL (pdMBL) in MBL-deficient pediatric oncology patients, we found that despite MBL trough levels above 1.0μg/ml MBL functionality was not efficiently restored upon ex vivo testing. PdMBL showed C4-converting activity by itself, indicating the presence of MASPs. Upon incubation of pdMBL with MBL-deficient sera this C4-converting activity was significantly reduced. Depletion of the MASPs from pdMBL, paradoxically, restored the C4-converting activity. Subsequent depletion or inhibition of C1-inh, the major inhibitor of the lectin pathway, in the recipient serum restored the C4-converting activity as well. Complexes between MBL/MASPs and C1-inh (MMC-complexes) were detected after ex vivo substitution of MBL-deficient serum with pdMBL. These MMC-complexes could also be detected in the sera of the patients included in the MBL-substitution study shortly after pdMBL infusion. Altogether, we concluded that active MBL–MASP complexes in pdMBL directly interact with C1-inh in the recipient, leading to the formation of a multimolecular complex between C1-inh and MBL/MASPs, in contrast to the classical pathway where C1r and C1s are dissociated from C1q by C1-inh. Because of the presence of activated MASPs in the current pdMBL products efficient MBL-mediated host protection cannot be expected because of the neutralizing capacity by C1-inh.