PMC

Influenza-specific IgA reactivity is enriched in PPAb than sera. IgA and IgG binding titers against TIV were determined by ELISA.

Influenza-specific IgG and IgA binding reactivity of PPAb on day 0 (d0) and day 7 (d7) after vaccination. ELISA plates were coated with 2008 TIV. OD_450nm values of 1:10 serially diluted PPAb samples were plotted against dilution factors (A, C) or PPAb concentration (B, D).

Influenza-specific functional reactivity against vaccine viruses are enriched in PPAb than serum. Functional titer is defined as the geometric mean of neutralization or HAI titer against each of the 3 vaccine component viruses. Neutralization titer of <10 (for PPAb) or <20 (for sera) is assigned a value of 5 or 10, respectively. HAI titer of <4 is assigned a value of 2. Binding titer is defined as the sum of ELISA IgA titer and IgG titer against TIV.

Patterns of influenza virus-specific binding reactivity in PPAb differ from those in serum. PPAb (day 7) and serum (day 28) samples from 3 subjects were tested for IgA and IgG reactivity in ELISA plates coated with the 2008 TIV or its individual component viruses. Distinct patterns of relative reactivity against the 3 different vaccine strains in PPAb versus sera are labeled with different color arrows.

Secretion of PPAb from cultured B cells. B cells collected from 5 subjects (No. 1 – No. 7) at different days after influenza vaccination were cultured at 3 million/ml for one week. A. Concentration of IgG and IgA in the conditioned media. The bars depict mean concentration. B. Linear regression between the concentration of PPAb and number of total ASC in culture of B cells collected on day 7 after vaccination. The number of IgA and IgG ASC in cultured B cells was determined with ELISPOT. IgG ELISPOT result is not available for subject No. 1.

Secretion of PPAb from total B cells and sorted plasmablast (PB) subsets. Total B cells, or sorted IgA⁺ subset (13,000 cells) and IgA⁻ subset (80,000 cells) of CD27^highCD38^high PB mixed with homologous CD3⁺ cells (as feeder cells), were cultured for 7 days. The expression of surface IgG was down-modulated on IgG PB, compared to IgG memory B cells. Concentration of IgG and IgA in culture media was measured by ELISA. This is the representative data of two experiments conducted with day 7 post influenza vaccination blood samples from donors No. 6 and No. 7, respectively, with similar results.