Human germinal centres engage memory and naive B cells after influenza vaccination
Influenza viruses remain a major public health threat. Seasonal influenza vaccination in humans primarily stimulates pre-existing memory B cells, leading to a transient wave of circulating antibody-secreting plasmablasts1–3. This recall response contributes to “original antigenic sin,” the selective boosting of antibody specificities from prior exposures to influenza virus antigens4. It remains unclear whether such vaccination can also induce germinal centre (GC) reactions in the draining lymph node (LN) where diversification and maturation of recruited B cells can occur5. Here we used ultrasound-guided fine needle aspiration to serially sample the draining LNs and investigate the dynamics and specificity of GC B cell responses after influenza vaccination in humans. We show that influenza vaccine-binding GC B cells can be detected as early as 1 week after vaccination. In 3 out of 8 participants, we detected vaccine-binding GC B cells up to 9 weeks after vaccination. Between 12% and 88% of the responding GC B cell clones overlapped with those detected among early circulating plasmablasts. These shared B cell clones had high frequencies of somatic hypermutation (SHM) and encoded broadly cross-reactive monoclonal antibodies (mAbs). In contrast, vaccine-induced B cell clones detected only in the GC compartment exhibited significantly lower SHM frequencies and predominantly encoded strain-specific mAbs, suggesting a naive B cell origin. Electron microscopy-based epitope mapping revealed that some of these strain-specific mAbs recognized epitopes that were not targeted by the early plasmablast response. Our results indicate that influenza virus vaccination of humans can elicit a GC reaction to which B cell clones targeting novel epitopes are more likely to be recruited, thereby broadening the spectrum of vaccine-induced protective antibodies against this rapidly mutating pathogen.
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