Cross-subtype immunity against avian influenza in humans recently vaccinated for the influenza season

Abstract number: 1732_230

Capobianchi M., Castilletti C., Gioia C., Bordi L., Agrati C., Tempestilli M., Chiappini R., Piacentini P., Squarcione S., Ippolito G., Poccia F.

Objectives: Avian H5N1 influenza viruses could be transmitted to humans, resulting in severe or fatal disease. Aim of this study was to evaluate the immune cross-reactivity between human and avian (H5N1) influenza strains in healthy donors vaccinated for seasonal H1N1/H3N2 influenza A.

Methods: Healthcare workers wishing to receive seasonal influenza vaccination at the Spallanzani Institute were enrolled. Blood samples for the assessment of humoral and cell-mediated responses were obtained before and 30 days after vaccination. The frequency of circulating antigen-specific CD4 and/or CD8 T-cells in healthy donors enrolled in the study were analysed by flow cytometry, using intracellular cytokine staining assay after the expansion of effector-cells in vitro. Human sera from the same donors were tested for their HA-inhibition activity against vaccine preparation and neutralisation activity against H5N1 virus.

Results: Our data indicate that vaccination may boost cross-subtype cellular and/or humoral immunity against H5N1 influenza. Specifically, H5N1-specific CD4 T-cell frequency was significantly higher in pluri-vaccinated versus first flu-vaccinated donors. The main target for cross-reactivity between H5N1 and H3N2/H1N1 strains was N1. No correlation between influenza-specific CD4 T-cells and humoral response was observed, suggesting that this response was mainly CD4 T-cell-independent. Differently, CD4 T-cells may help for anti-influenza CD8 T-cell response. Furthermore, human sera from the same donors, tested for their HA-inhibition activity against vaccine preparation, showed a significant rise (73.7%) after vaccination. The same sera were tested for their H5N1 neutralisation activity and 34.2% of subjects was able to show anti-H5N1 antibody rise after seasonal influenza vaccination, showing the existence of an antibody-dependent cross-type immunity. No correlation between influenza specific CD4 T-cells and humoral responses were observed, suggesting that this type of antibody response was mainly CD4 T-cell independent.

Conclusion: In this study, we demonstrated that vaccination against seasonal influenza might induce both cellular and humoral cross-reactive immunity against H5N1 avian influenza. This cross-type immunity may represent an important component of the immune response against novel influenza A infections.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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