Observation of immune responses and heterosubtypic protection induced by an inactivated avian influenza H5N1 vaccine in mice

Abstract

Objective To observe immune responses and heterosubtypic protection elicited by an inactivated influenza H5N1 vaccine with different immunization routes in mice. Methods BALB/c mice were intraperitoneally injected or intranasally immunized with the inactivated H5N1 vaccine, the mice administered with PBS were used as control. Weight loss and survival in mice were observed after PR8 or a H9N2 virus challenge. Serum specific IgG antibody and its subclasses were detected by ELISA kits. Ratios of CD4+ /CD8+ lymphocytes in spleens of mice were assayed. The t-test was used in the comparison of different groups.Results After challenge, weight loss was found in all groups, but the weight of mice in vaccination groups returned to normal later. The mice in PBS groups all died. The vaccinated mice were completely protected against PR8 and partly protected against H9N2 virus. The level of IgG antibody increased significantly after vaccination, and the increase magnitude of IgG2a was higher than that of IgG1. The ratios of CD4+ /CD8+ lymphocytes in spleens of vaccinated mice decreased after challenge (t=6. 8017,P<0. 01) , especially in the intranasal group (t = 3. 9701, P < 0. 05 ). Conclusions Both intraperitoneal injection and intranasal immunization can induce a high level of specific IgG, especially the level of IgG2a, and provide protection against heterosubtypic viruses. Intranasal immunization seems to induce a higher level of CD8+ T cell response. Key words: Influenza A virus,H5N1 subtype; Influenza vaccine; Injections,intraperitoneal; Administration,intranasal; Cross protection