FIG. 5.

Intranasal, but not intraperitoneal, immunization induces antigen-specific IgA production in the upper respiratory tract. Immunization groups are designated as described in Table 4. All immunizations were performed with inactivated influenza virus vaccine plus 0.1 μg of CT. Nasal washes were collected 14 days after primary immunization. The results are from samples collected from three experiments. The single asterisk denotes statistical differences (P ≤ 0.05) from values for all other immunization groups.