Plasmablast and antibody secreting cell response. The frequency of peripheral blood plasmablasts (IgD-CD24-CD27++CD38++) among total CD19+ B cells was determined by flow cytometry at baseline, day five to day seven, and day eight to day ten following vaccination with seasonal trivalent influenza vaccine (TIV). (a) Identification of plasmablasts from representative subjects at day five to day seven following 2010-2011 TIV. Plots are gated on live, CD3-CD19+IgD-CD24- cells. (b) Fold change in plasmablast frequency over baseline following 2009-2010 TIV is indicated. (c) TIV IgG-specific EliSpots were performed on total peripheral blood mononuclear cells (PBMC) following 2009-2010 TIV. The red star indicates significant difference (P < 0.05) as compared with healthy control (HC) group, the blue star indicates significant difference as compared with rheumatoid arthritis (RA) group. Each symbol represents an individual study subject, red line indicates group mean.