Immunological responses to influenza vaccination: lessons for improving vaccine efficacy.

A critical factor in the maturation of influenza vaccine responses is the nearly inevitable binding of vaccine antigens by exiting anti-influenza IgGs. These antigen-IgG immune complexes direct the response to immunization by modulating cellular processes that determine antibody and T-cell repertoires: maturation of dendritic cells, processing and presentation of antigens to T cells, trafficking of antigens to the germinal center, and selection of B cells for antibody production. By focusing on the recent advances in the study of the immunomodulatory processes mediated by IgG immune complexes upon influenza vaccination, we discuss a pathway that is critical for modulating the breadth and potency of anti-HA antibody responses and has previously led to the development of strategies to improve influenza vaccine efficacy.