Immune responses and protection in different strains of aged mice immunized intranasally with an adjuvant-combined influenza vaccine

Immune responses and protection against influenza virus infection were comp ared between young (2 months) and aged (18 months) BALB/c, C3H and C57BL/6 (B6) mice after intranasal vaccination. The mice were immunized with 2.5 mu g protein of A/PR/8/34 (PRs) (H1N1) virus vaccine containing a cholera toxi n adjuvant. In both the young and aged BALB/c mice, high levels of PR8-spec ific antibody-forming cell (AFC) responses were induced in the nasal-associ ated lymphoid tissue (NALT) 7 days after immunization. Nasal wash IgA and s erum IgG antibody (Ab) responses to the PR8 haemagglutinin (HA) 4 weeks aft er immunization were slightly higher in the young mice than in the aged mic e. The young mice showed complete protection against challenge infection, w hile the aged mice showed only a partial protection. In the C3H mice, NALT- AFC, and IgA and IgG Ab responses were higher in the young mice than those in the aged mice in pallarel with the more efficient protection in the youn g mice than in the aged mice. Both the young and aged B6 mice showed no NAL T-AFC responses, scarce IgA and IgG Ab responses and no protection. In the BALB/c mice, IgG1 and IgG2a levels were significantly lower in the aged mic e. On the other hand, in the C3H mice, only IgG2a level was significantly l ower in the aged mice. Similar results were obtained in terms of immune res ponses and protection between the young and aged mice of three different st rains of mice after intra-nasal immunization with 0.1 mug of PR8 vaccine co ntaining the adjuvant, two-times at 4-week intervals. In the B6 mice, the i mmune response was improved by immunization with a higher dose of the adjuv ant-combined vaccine. These results suggest that local Ab responses, as wel l as systemic Ab responses, are downregulated in aged mice, although the de gree of the downregulation of immune responses differs from strain to strai n. (C) 2001 Elsevier Science Ltd. All rights reserved.