Prior antibodies shape distinct immune responses to influenza vaccination

Influenza vaccination does not produce the same immune response in every person. Although seasonal vaccines are reformulated to match viruses expected to circulate, the quality and breadth of protection generated after immunization can be shaped by a person’s previous encounters with influenza viruses and earlier vaccines. These prior exposures leave behind antibodies and memory B cells that can influence how the immune system recognizes and responds to a new vaccine. A study published in Virologica Sinica now provides evidence that pre-existing antibody levels are associated with distinct patterns of B-cell maturation and antibody development after seasonal influenza vaccination. The findings offer a more detailed view of how immune history may direct subsequent responses to influenza and could help inform strategies for designing vaccines capable of overcoming differences between individuals.

The investigation followed 21 adults before and after seasonal influenza vaccination. The researchers grouped participants according to their baseline levels of antibodies directed against hemagglutinin, or HA, the major surface glycoprotein used by influenza viruses to attach to and enter host cells. HA-specific antibody titers provide an indication of existing humoral immunity, but they do not fully describe the cellular processes that generate or refine antibody responses. To examine those processes, the team combined flow cytometry with B-cell receptor sequencing and monoclonal antibody characterization. This integrated approach enabled the scientists to track changes in HA-binding B-cell populations, analyze immunoglobulin gene sequences, and test the binding and neutralizing properties of antibodies produced by individual B-cell lineages.

The researchers identified clear differences in the HA-binding B-cell responses of people with different pre-vaccination antibody levels. Participants with higher baseline titers showed increased frequencies of HA-positive B cells carrying a naive-like phenotype, defined by expression of CD27 and IgD markers consistent with less antigen-experienced cells. Naive B cells have not undergone the extensive selection and refinement typically associated with mature memory responses. Their greater representation after vaccination suggests that individuals with substantial pre-existing antibody may recruit or maintain B-cell populations that have experienced less maturation, rather than exclusively reactivating highly evolved memory lineages generated by earlier influenza exposures.

B-cell receptor sequencing provided additional evidence that the antibody response differed according to baseline immunity. B-cell receptors, which are membrane-bound forms of antibodies, carry genetic signatures of a cell’s developmental history. During an immune response, activated B cells can undergo somatic hypermutation, a process that introduces mutations into antibody variable-region genes. Cells whose receptors acquire advantageous mutations may be preferentially selected and expanded, improving their ability to recognize antigen. The study found that B-cell receptors associated with participants in the lower-titer groups displayed greater levels of mutation than those observed in the higher-titer groups. This pattern is consistent with a response involving more extensively matured antibody lineages.

The lower-titer groups also showed broader class switching. B cells initially produce antibodies such as immunoglobulin M before switching to other antibody classes, including immunoglobulin G, which can have different tissue distributions and functional properties. Class-switch recombination changes the constant region of the antibody without altering the antigen-binding sequence, allowing an immune response to acquire new biological functions while retaining target recognition. More extensive class switching, together with higher mutation levels, indicated that B-cell lineages in the lower-baseline-antibody participants had undergone a greater degree of evolutionary refinement. The researchers’ analysis therefore linked reduced pre-existing HA antibody levels with a response that appeared more mature at the molecular level.

The functional properties of antibodies generated by these lineages reinforced the sequencing results. Monoclonal antibodies from the lower-titer groups demonstrated broader neutralizing activity against historical influenza strains, suggesting that they recognized conserved features shared across viruses from different periods. Neutralization is a particularly important measure because antibody binding alone does not necessarily prevent infection. Antibodies that block viral attachment, interfere with membrane fusion, or otherwise inhibit productive replication can provide more meaningful protection. The broader activity observed in the lower-titer group indicates that the associated B-cell lineages were not simply producing more antibodies, but were generating antibodies with a wider capacity to counter antigenically diverse influenza viruses.

By contrast, the response associated with higher pre-vaccination antibody levels appeared to contain a larger contribution from less-mature B-cell populations. One possible explanation is that abundant circulating antibodies may alter the amount, form, or persistence of vaccine antigen available to stimulate B cells. Pre-existing antibodies can bind antigen and influence its transport, uptake, and presentation, potentially changing which B-cell clones receive activation signals. They may also create selective conditions in which some previously generated lineages are inhibited while other, less-experienced populations are recruited. The present study establishes an association rather than proving a single mechanism, but its results support the idea that baseline antibody concentrations can shape the cellular pathway followed after vaccination.

The findings also illustrate why vaccine responses cannot be evaluated solely by measuring the overall concentration of antibodies in blood. Two individuals may reach similar post-vaccination antibody levels while producing antibodies with different degrees of mutation, class switching, lineage diversity, or cross-strain activity. By examining B-cell phenotypes, receptor sequences, and monoclonal antibody function together, the researchers were able to distinguish these qualitative features. Such information may be particularly valuable for influenza, where antigenic drift continually changes the HA proteins targeted by immunity. A response focused on strain-specific sites may lose effectiveness as the virus evolves, whereas antibodies recognizing conserved regions could retain activity across multiple seasons.

The study adds to growing evidence that immune history is an important determinant of vaccine performance. Previous infections and vaccinations are not simply cumulative sources of protection; they can redirect the composition and evolution of later B-cell responses. The researchers emphasize that different pre-existing antibody levels were associated with different patterns of maturation and antibody breadth following influenza vaccination. Further studies involving larger and more diverse populations will be needed to determine whether the same relationships occur across age groups, vaccine formulations, influenza subtypes, and repeated vaccination histories. Nonetheless, the work provides a framework for investigating how baseline immunity influences vaccine-induced B-cell evolution and may support the development of influenza vaccines designed to promote broadly neutralizing antibodies despite substantial variation in individual immune backgrounds.

Web References: https://doi.org/10.1016/j.virs.2026.08.007

References: Wang W, Sun Y, Liu Q, Xia Y, Wang J, Hu M, Kong M, He J, Gao R, Gao Y. “Pre-existing hemagglutinin-specific antibody levels are associated with B-cell repertoire maturation and antibody breadth after influenza vaccination.” Virologica Sinica. DOI: 10.1016/j.virs.2026.08.007