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Evaluation of the relative in vitro activities of various forms of CRIg
Author(s) -
Embuscado Lizette,
Chinn Jason,
Loyet Kelly,
Katschke Kenneth,
Van Lookeren Campagne Menno,
DeForge Laura
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.2_supplement.395
Subject(s) - complement receptor , avidity , alternative complement pathway , microbiology and biotechnology , complement system , chemistry , antibody , biology , genetics
Complement receptor of the immunoglobulin superfamily (CRIg) binds to C3b and thereby selectively inhibits the alternative complement pathway (AP). Given the potential therapeutic utility of CRIg in conditions involving inappropriate activation of complement, the inhibitory activities of various forms of CRIg were evaluated in vitro in order to guide the selection of a possible clinical candidate. The extracellular domains (ECDs) of two splice variants of human CRIg (long, 24 kDa; short, 14 kDa) were produced. The ECDs were also expressed as bivalent IgG1 Fc fusion proteins, both with and without a short glycosylated stalk region. These molecules were evaluated in AP‐selective fluid‐phase and solid‐phase assays. In addition, we performed two types of competitive binding assays to determine the relative affinities of the CRIg molecules for C3b. Overall, the results of the binding assays agreed well with the enzymatically‐driven assays and showed that the CRIg‐Fc versions were substantially more potent when C3b was presented as a multimer, likely due to avidity effects, whereas long CRIg ECD was nearly as potent as CRIg‐Fc when C3b was presented as a monomer in solution. Stalkless CRIg‐Fc was less active than the stalked versions. These studies demonstrate that different forms of CRIg vary substantially in their activities depending on the structure of the molecule as well as the valency of its target C3b.