NATURAL-KILLER-CELL CYTOTOXICITY IN ELDERLY HUMANS AFTER INFLUENZA IMMUNIZATION

Previous studies have reported that human natural killer (NK) cytotoxi city can be augmented by either in vitro stimulation with influenza vi rus antigens or in vivo administration of killed influenza vaccine. Th e study demonstrating the latter conclusion reported an increase in NK cytotoxicity lasting for 4 weeks postvaccination in young subjects. W e initiated our study to determine if a similar increase in NK activit y was observed in an elderly population after immunization with the 19 92-1993 influenza vaccine. NK activity of 34 elderly (mean age, 77.3 y ears) was determined at 3 time points: prevaccination, 4 to 6 weeks po stvaccination, and 5 to 6 months after vaccination. In contrast: to th e results of the previous study, the NK cytotoxicity of our elderly su bjects was not augmented by the influenza vaccine at any time tested. We also determined the number of CD56(+) cells in whole-blood samples at each of the time points and found that there is no change in NK cel l number after influenza vaccination.