Comparative antibody responses and protection in mice immunised by oral or parenteral routes with influenza virus subunit antigens in aqueous form or incorporated into ISCOMs

The total and subclass antibody responses of mice and protection of these animals against live influenza A/Sichuan/2/87 virus challenge infection were determined after immunisation with homologous A/Sichuan/87 aqueous or ISCOM-formulated surface glycoprotein subunit antigens administered by either the oral or intramuscular routes. The results show that the greatest systemic and local antibody responses were elicited in mice immunised with A/Sichuan ISCOMs by the intramuscular route; protection against homologous virus challenge was also effective in these animals, particularly after two doses of the vaccine. However, relatively high immune responses and protection were also elicited by the A/Sichuan/87 ISCOM vaccine administered orally. Immunisation of mice by the intramuscular route resulted in levels of serum IgG2a subclass antibody significantly greater than those induced by the same preparation given by the oral route, or by the aqueous A/Sichuan/87 subunit antigen preparation administered by either route. The findings indicate that the ISCOM delivery system can be used for immunisation by the oral route, although in mice, under the conditions used, this strategy compares unfavourably with the intramuscular route in terms of both local and systemic immune responses and protection against homologous challenge virus infection.