Background.  Annual vaccination is the primary means for preventing influenza. However, great interindividual variability exists in vaccine responses, the cellular events that take place in vivo after vaccination are poorly understood, and appropriate biomarkers for vaccine responsiveness have not been developed.

Methods.  We immunized a cohort of healthy male adults with a licensed trivalent influenza vaccine and performed a timed assessment of global gene expression before and after vaccination. We analyzed the relationship between gene expression patterns and the humoral immune response to vaccination.

Results.  Marked up regulation of expression of genes involved in interferon signaling, positive IL-6 regulation, and antigen processing and presentation, were detected within 24 hours of immunization. The late vaccine response showed a transcriptional pattern suggestive of increased protein biosynthesis and cellular proliferation. Integrative analyses revealed a 494-gene expression signature—including STAT1, CD74, and E2F2—which strongly correlates with the magnitude of the antibody response. High vaccine responder status correlates with increased early expression of interferon signaling and antigen processing and presentation genes.

Conclusions.  The results highlight the role of a systems biology approach in understanding the molecular events that take place in vivo after influenza vaccination and in the development of better predictors of vaccine responsiveness.