Route of administration is the prime determinant of IgA and IgG2a responses in the respiratory tract of mice to the cold-adapted live attenuated influenza a donor strain A/Leningrad/134/17/57

Serum antibody and antibody secretory cell (ASC) responses to the cold-adapted (CA) live attenuated influenza A donor strain A/Leningrad/134/17/57 in BALB/c mice were determined in the lungs and mediastinal lymph nodes after administration by the intranasal, subcutaneous and intramuscular routes. Both types of response were greatest when an inoculum consisting of 106.5 50% egg infectious doses (EID50) was administered twice intranasally at an interval of 3 weeks. Serum responses by the intramuscular route were much higher than by the subcutaneous route but, at doses of 106.5-7.5 EID50, were still lower than that obtained with two doses of an intranasal inoculum of 106.5 EID50. Virus-specific ASC responses for IgA and IgG2a were obtained in the lungs and mediastinal lymph nodes of mice inoculated with 106.5 EID50 by the intranasal route. However, ASC responses after inoculation by either the subcutaneous or intramuscular routes were barely detectable, even at doses as high as 107.5 EID50. These results confirm that intranasal administration of live vaccines induces far higher virus-specific IgA and IgG2a responses in the respiratory tract of mice than can be achieved by parenteral administration and that serum antibody levels induced by parenteral vaccination are unrelated to the respiratory ASC response.