Cord blood lymphocyte in vitro responses to influenza A antigens after an epidemic of influenza A/Port Chalmers/73 (H3N2).

Samples of cord blood from 46 deliveries were collected between 2 and 8 mo after an epidemic of influenza caused by A/Port Chalmers/73 (H3H2) virus. Of 10 samples with HAI antibody titers against A/Port Chalmers of 1:16 or greater, one had 2-mercaptoethanol-sensitive IgM class antibodies against the virus. Lymphocyte proliferative responses with the use of A/Port Chalmers antigens were increased in six of 46 samples. These results provide immunologic evidence that certain neonates have IgM antibodies and lymphocytes sensitized for influenza A virus. Our results suggest, but do not prove definitively, that influenza A/Port Chalmers virus infected the fetus prior to delivery.