Immune response to influenza vaccination in healthy adults

Evaluation of specific immune response in immunized humans has been considered as the only reliable indicator of protective immunity. Antiviral immunity has usually been assessed by antiviral antibody titre determination in paired sera. This method evaluates the capacity of B cells to secrete antiviral antibodies while T cells, as the most important cells in antiviral immune reactions, are not directly analyzed. Sensitive assay using HLA class I tetramers was used to detect low-frequency antigen-specific T cells directed against influenza viral antigens in 13 healthy HLA-A*0201+ influenza vaccinated (Agrippal, Chiron, Italy) adult humans. Peripheral blood mononuclear cells and sera were isolated before, and 7, 14 days and 28 days after vaccination. Four colour flow cytometry following the direct ex vivo tetramer staining of recently activated CD8+ T-lymphocytes was used for monitoring of T cell response specific for HLA-A*0201-restricted influenza A matrix antigen (M158-66) and haemaglutinin antigens (A/New Caledonia/H1N1, HA345-354, HA542-550). Influenza-specific T cell lines were generated and used as a positive control. Inhibition of hemagglutination (IH) assay was used for detection of specific antiviral antibodies titre in sera. In eleven individuals the increase of antibody titre and frequency of antigen-specific T cells were observed after vaccination. The frequency of recently activated HA542-550 and M158-66 specific CD8+ T cells significantly increased 28 days after vaccination. No changes were observed in the number of HA345-354 specific T cells. Vaccine specific antibody response significantly increased 14 and 28 days after vaccination. Our results indicate that MHC tetramer method could be used for evaluation of specific immune response and detection of protective immunity in vaccinated individuals.