Upon vaccination, B cells differentiate into antibody secreting cells (ASCs) that migrate via the circulation to tissues. The kinetics of this response and the relationship of circulating ASCs to protective antibody titers have not been completely explored.

Influenza-specific and total-IgG ASCs were enumerated by Elispot and flow cytometry daily in the blood in 6 healthy adults after trivalent influenza vaccination (TIV).

Peak H1-specific IgG ASC frequencies occurred variably from day 5 to 8 and correlated with the fold-rise rise in hemagglutination inhibition (HAI titers); r=0.91, p=0.006. H3-specific IgG ASC frequencies correlated less well, perhaps due to a mismatch of the H3 protein in the vaccine and that used in the Elispot assay. Peak frequencies of vaccine-specific and total-IgG ASCs were 0.3% and 0.8%, respectively, of peripheral blood mononuclear cells (PBMC). Peak TIV-, H1-, H3-, and total-IgG ASC frequencies were 1736±1133, 626±520, 592±463, and 4091±2019 spots/10⁶ PBMC, respectively. Peak TIV-, H1-, and H3-specific IgG ASC of total-IgG ASC frequencies constituted 63%±21, 26%±10, 22%±17, respectively.

After immunization with inactivated influenza vaccine the peak in influenza-specific ASC frequencies is variable but correlates well with the magnitude of protective HAI responses.