Comparison of the cross-reactive anti-influenza neutralizing activity of polymeric and monomeric IgA monoclonal antibodies.

Here we examined whether polymeric IgA (pIgA) and monomeric IgA (mIgA) antibodies differ in their ability to neutralize drift viruses within the same subtype. We used an IgA monoclonal antibody (mAb; H1-21) against influenza virus strain A/Hiroshima/52/2005 (A/Hiroshima; H3N2). The mAb was obtained after immunizing mice mucosally with a split-virion (SV) vaccine. The mAb contained both mIgA and pIgA forms. It reacted with the homologous virus and cross-reacted with drift viruses A/New York/55/2004 (H3N2) and A/Wyoming/3/2003 (H3N2) in hemagglutinin-inhibition (HI) and neutralizing Ab assays. The mAb also cross-reacted with A/Panama/2007/99 (H3N2) in an ELISA. We separated the mAb into pIgA and mIgA fractions by gel filtration, and then tested them for neutralizing Ab activity. The neutralizing activity for the A/Hiroshima/52/2005, A/New York/55/2004, and A/Wyoming/3/2003 viruses was lower for the mIgA than the pIgA fraction. However, the neutralizing efficiency for drift variants relative to that for the homotype did not differ between pIgA and mIgA, and pIgA only neutralized variants that could also be neutralized by mIgA. These results suggest that the polymerization of IgA enhances its antiviral immune responses, but does not increase the number of influenza virus strains neutralized by the IgA.