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#Detection of low pre-existing #humoral #immunity against #influenza virus #H5N1 clade 2.3.4.4b in unexposed individuals

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By G.M.

Abstract

The repeated spill-over of Influenza A virus H5N1 clade 2.3.4.4b from cattle to humans highlights the risk of a human H5N1 pandemic. Given the impact of pre-existing immunity on the course and severity of viral infections, we assessed in detail the humoral immunity against the H5N1 A/Texas/37/2024 isolate in H5N1-naive individuals. To this end, we performed complementary binding and neutralization assays on 66 subjects and ranked activities among a panel of 76 influenza A virus isolates. We detected low but distinct cross-neutralizing titers against A/Texas/37/2024 with a 3.9 to 15.6-fold reduction compared to selected H1N1 or H3N2 strains. Moreover, by cloning and evaluating 136 monoclonal antibodies from single memory B cells, we identified potent A/Texas/37/2024-neutralizing monoclonal antibodies in five out of six investigated individuals. These antibodies predominantly utilize VH1-69 gene segments, cross-neutralize H1, and compete with antibodies targeting the HA stem. Our findings demonstrate partial pre-existing humoral immunity to A/Texas/37/2024 in H5N1-naive individuals.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.01.22.634277v1

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