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Parameters of humoral and cellular immunity of influenza A/USSR/90/77 (H1N1) virus in various age groups.

After a local epidemic of A/USSR influenza, immunologic parameters related to influenza A/USSR/90/77 (H1N1) virus were studied in four age groups: elderly persons (greater than or equal to 64 years), healthy adults (20-44 years), children (six to 13 years), and neonates (who served as controls). Sera from the first three groups had nearly equivalent titers of hemagglutination-inhibiting antibody (geometric mean titers, 1:8-1:11), which were greater than those in cord blood of neonates. Lymphocyte proliferation responses to influenza A/USSR viral antigens among study groups were similar, with mean stimulation ratios (to whole virus) of 4.2-5.4; neonatal cord blood samples were unresponsive (stimulation ratio, 1.1). In contrast, the magnitude of antibody-dependent cellular cytotoxicity against baby hamster kidney target cells infected with influenza A/USSR virus was significantly greater with lymphocytes from adults and elderly persons (P less than 0.05) than with those from children.