<b>The CH1 domain influences the expression and antigen sensing of the HIV-specific CH31 IgM-BCR and IgG-BCR</b>

Membrane immunoglobulin class impacts the expression level and antigen binding features of the BCR. We studied the antigen sensing of human B cells expressing either an IgM- or IgG1-class BCR, with the same VH/VL domains namely that of the anti-HIV broadly neutralizing antibody (bnAb) CH31. We found that CH31 IgM-BCR and CH31 IgG-BCR differ in the levels of BCR expression and their binding and response to monomeric and tetrameric HIV antigens. These class-specific features of the IgG1-BCR could be transferred with the CH1g domain to a chimeric IgM(Cg1)-BCR. We suggest that the CH1g is more stable than the CH1m domain to allow the production of antigen receptors and antibodies with highly mutated and unstable VH domains.