Nasal plasmid Flt3 ligand and CpG ODN alone enhances immediate, influenza virus-specific recall secretory IgA Ab responses in aging (MUC1P.904)

Abstract

Abstract The elderly have already experienced various pathogens and thus possess pathogen-specific Abs, whose titers are too low to combat reinfection. Thus, it would be of great benefit to the aged population if one could use an innate adjuvant system alone, without vaccine, in order to enhance mucosal immunity against past respiratory infections. We tested whether a combined plasmid Flt3 ligand (pFL) and CpG ODN adjuvant would enhance influenza virus-specific recall Ab responses without a need for additional vaccination. Young adult mice were nasally immunized with A/Puerto Rico/8/34 (PR8) hemagglutinin (HA) plus cholera toxin as mucosal adjuvant three times at weekly intervals. Seven months later, these mice were given nasal pFL and CpG ODN only or combined adjuvant together with PR8 HA. Saliva and plasma samples were collected 7 days later and PR8 HA-specific IgA Ab responses were evaluated. Both groups of mice showed significantly increased and comparable levels of anti-PR8 HA secretory IgA Ab responses in saliva when compared with those responses seen without innate adjuvant. The increase in total IgG Ab responses in mice given pFL and CpG ODN were limited when compared with those seen after primary nasal immunization. Total plasma IgE Ab titers in mice given nasal pFL and CpG ODN only were the same as IgE levels seen in naïve mice. These results suggest that nasal pFL and CpG ODN alone can enhance pre-existing Ag-specific Ab responses without adverse effects in the elderly.