Abstract
Rheumatoid factors (RFs) are autoantibodies against the fragment-crystallizable (Fc) region of IgG. In individuals with hematological diseases such as cryoglobulinemia and certain B cell lymphoma forms, the RFs derived from specific heavy- and light-chain germline pairs, so-called "stereotypic RFs," are frequently produced in copious amounts and form immune complexes with IgG in serum. Of note, many structural details of the antigen recognition mechanisms in RFs are unclear. Here we report the crystal structure of the RF YES8c derived from the IGHV1-69/IGKV3-20 germline pair, the most common of the stereotypic RFs, in complex with human IgG1-Fc at 2.8 Å resolution. We observed that YES8c binds to the CH2-CH3 elbow in the canonical antigen-binding manner involving a large antigen-antibody interface. On the basis of this observation, combined with mutational analyses, we propose a recognition mechanism common to IGHV1-69/IGKV3-20 RFs: (1) the interaction of the Leu432-His435 region of Fc enables the highly variable complementarity-determining region (CDR)-H3 to participate in the binding, (2) the hydrophobic tip in the CDR-H2 typical of IGHV1-69 antibodies recognizes the hydrophobic patch on Fc, and (3) the interaction of the highly conserved RF light chain with Fc is important for RF activity. These features may determine the putative epitope common to the IGHV1-69/IGKV3-20 RFs. We also showed that some mutations in the binding site of RF increase the affinity to Fc, which may aggravate hematological diseases. Our findings unravel the structural basis for germline-encoded antibody autoreactivity.
Highlights
Rheumatoid factors (RFs) are autoantibodies against the fragment-crystallizable (Fc) region of IgG
On the basis of this observation, combined with mutational analyses, we propose a recognition mechanism common to IGHV1-69/IGKV3-20 RFs: [1] the interaction of the Leu432–His435 region of Fc enables the highly variable complementarity-determining region (CDR)-H3 to participate in the binding, [2] the hydrophobic tip in the CDR-H2 typical of IGHV1-69 antibodies recognizes the hydrophobic patch on Fc, and [3] the interaction of the highly conserved RF light chain with Fc is important for RF activity
In serum from healthy human donors immunized with mismatched red blood cells [12] as well as patients with mixed cryoglobulinemia (MC) caused by hepatitis C virus (HCV) infection [13], mucosa-associated lymphoid tissue–type lymphoma [14], HCV-associated lymphoma [15], and B cell chronic lymphocytic leukemia [16], high frequencies of RFs with combinations of heavy chains and light chains that are from specific germline genes, called “stereotypic RFs”, have been reported [17]
Summary
In patients with HCVassociated MC, IgM antibodies from IGHV1-69/IGKV3-20 have RF activity with or without somatic hypermutations [26]. Do the IGHV1-69/ IGKV3-20 RFs recognize the same epitope with the same binding mechanism? The crystal structures of two RFs have been determined in complex with Fc. Do the IGHV1-69/ IGKV3-20 RFs recognize the same epitope with the same binding mechanism? The crystal structures of two RFs have been determined in complex with Fc One of these is a RA patient– derived IgM rheumatoid factor, RF-AN, that recognizes the CH2–CH3 cleft via a site distal to the conventional antigen-binding site [28]. The other is a high-affinity IgM rheumatoid factor, RF61, that recognizes the CH3 domain close to the C terminus [29] These RFs are not stereotypic RFs and cannot provide answers to the aforementioned questions. Crystal structure and mutagenesis studies revealed a common mechanism used by a wide range of IGHV1-69/ IGKV3-20 stereotypic RFs to interact with the same position in the Fc fragment
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
