Anti-Idiotype scFv Localizes an Autoepitope in the Globular Domain of C1q

Immune Jumping in Autoimmune Long-Covid

This Long-Covid disease, mild or severe, is multiorgan or system-wide, spanning from fatigue to clotting abnormalities and autoantibody. The spectrum of different symptoms in Long-Covid diseases makes it difficult to point to a common immunopathogenic etiology. Different immune pathways are presented and critically evaluated. A hypothesis is advanced that indicates autoimmune reactions as cause for Long-Covid disease. The immune network pathway describes a redirection of the nominal anti-SARS-CoV response towards an autoimmune target. Several therapeutic interventions are suggested to suppress the autoimmune pathway.

Galectin-3 - A novel ligand of complement protein C1q

In the present study we report a novel interaction of human C1q, a primary activator of the Complement system, with human Galectin-3 (Gal-3). We investigated the potential recognition between C1q and Gal-3 on a solid hydrophobic surface by ELISA, by fluorescence spectroscopy, molecular docking and molecular dynamics (MD). The data showed that C1q and Gal-3 had a pronounced affinity for protein-protein interaction and supramolecular binding, locating the binding sites within the globular domains of C1q (gC1q) and on the backside of the carbohydrate recognition domain (CRD) of Gal-3. Fluorescence spectroscopy gave quantitative assessment of the recognition with KD value of 0.04 μM. MD analysis showed that when the active AAs of the two proteins interacted, electrostatic attraction, aided by a large number of hydrogen bonds, was dominant for the stabilization of the complex. When the contact of C1q and Gal-3 was not limited to active residues, the complex between them was stabilized mainly by Van der Waals interactions and smaller in number but stronger hydrogen bonds. This is the first report analyzing the interaction of Gal-3 with C1q, which could open the way to new applications of this protein-protein complex.