Abstract
Cleavage of the mammalian plasma protein C4 into C4b initiates opsonization, lysis, and clearance of microbes and damaged host cells by the classical and lectin pathways of the complement system. Dysregulated activation of C4 and other initial components of the classical pathway may cause or aggravate pathologies, such as systemic lupus erythematosus, Alzheimer disease, and schizophrenia. Modulating the activity of C4b by small-molecule or protein-based inhibitors may represent a promising therapeutic approach for preventing excessive inflammation and damage to host cells and tissue. Here, we present seven nanobodies, derived from llama (Lama glama) immunization, that bind to human C4b (Homo sapiens) with high affinities ranging from 3.2 nM to 14 pM. The activity of the nanobodies varies from no to complete inhibition of the classical pathway. The inhibiting nanobodies affect different steps in complement activation, in line with blocking sites for proconvertase formation, C3 substrate binding to the convertase, and regulator-mediated inactivation of C4b. For four nanobodies, we determined singleparticle cryo-electron microscopy structures in complex with C4b at 3.4-4 Å resolution. The structures rationalize the observed functional effects of the nanobodies and define their mode of action during complement activation. Thus, we characterized seven anti-C4b nanobodies with diverse effects on the classical pathway of complement activation that may be explored for imaging, diagnostic, or therapeutic applications.
Original language | English |
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Pages (from-to) | 2207-2219 |
Number of pages | 13 |
Journal | Journal of Immunology |
Volume | 208 |
Issue number | 9 |
DOIs | |
Publication status | Published - 1 May 2022 |
Bibliographical note
Funding Information:This work was supported by Consejo Nacional de Ciencia y Tecnología in Mexico (CVU 604718), by the European Research Council under the European Union’s Horizon 2020 Framework Programme Grant Agreement No. 787241, and by Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Project No. 01.80.104.00).
Publisher Copyright:
© 2022 TheAuthors.
Funding
This work was supported by Consejo Nacional de Ciencia y Tecnología in Mexico (CVU 604718), by the European Research Council under the European Union’s Horizon 2020 Framework Programme Grant Agreement No. 787241, and by Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Project No. 01.80.104.00).