Dual stimulation by autoantigen and CpG fosters the proliferation of exhausted rheumatoid factor-specific CD21(low) B cells in hepatitis C virus-cured mixed cryoglobulinemia

• Published in: Frontiers in immunology Vol. 14
• Main Authors: Del Padre, M., Marrapodi, R., Minafo, Y. A., Mortari, E. P., Radicchio, G., Bocci, C., Gragnani, L., Camponeschi, Alessandro, Colantuono, S., Stefanini, L., Basili, S., Carsetti, R., Fiorilli, M., Casato, M., Visentini, M.
• Format: Journal Article
• Language: English
• Published: 08.02.2023
• Subjects: activation; antigen receptor; autoantigen; BCR; CD21(low) B; cells; exhaustion; expansion; Immunologi inom det medicinska området; Immunology; Immunology in the medical area; infection; innate; leukemia; lymphomas; lymphoproliferative disorders; marginal zone-like; mixed cryoglobulinemia; population; rheumatoid factor; TLR9 crosstalk
• ISSN: 1664-3224; 1664-3224
• DOI: 10.3389/fimmu.2023.1094871

IntroductionHepatitis C virus (HCV) causes mixed cryoglobulinemia (MC) by driving clonal expansion of B cells expressing B cell receptors (BCRs), often encoded by the VH1-69 variable gene, endowed with both rheumatoid factor (RF) and anti-HCV specificity. These cells display an atypical CD21low phenotype and functional exhaustion evidenced by unresponsiveness to BCR and Toll-like receptor 9 (TLR9) stimuli. Although antiviral therapy is effective on MC vasculitis, pathogenic B cell clones persist long thereafter and can cause virus-independent disease relapses. MethodsClonal B cells from patients with HCV-associated type 2 MC or healthy donors were stimulated with CpG or heath-aggregated IgG (as surrogate immune complexes) alone or in combination; proliferation and differentiation were then evaluated by flow cytometry. Phosphorylation of AKT and of the p65 NF-kB subunit were measured by flow cytometry. TLR9 was quantified by qPCR and by intracellular flow cytometry, and MyD88 isoforms were analyzed using RT-PCR. DiscussionWe found that dual triggering with autoantigen and CpG restored the capacity of exhausted VH1-69pos B cells to proliferate. The signaling mechanism for this BCR/TLR9 crosstalk remains elusive, since TLR9 mRNA and protein as well as MyD88 mRNA were normally expressed and CpG-induced phosphorylation of p65 NF-kB was intact in MC clonal B cells, whereas BCR-induced p65 NF-kB phosphorylation was impaired and PI3K/Akt signaling was intact. Our findings indicate that autoantigen and CpG of microbial or cellular origin may unite to foster persistence of pathogenic RF B cells in HCV-cured MC patients. BCR/TLR9 crosstalk might represent a more general mechanism enhancing systemic autoimmunity by the rescue of exhausted autoreactive CD21low B cells.