Vaccinations are often unsuccessful in preventing infection among elderly populations because of generally poor humoral immune responses. We have used tetanus toxoid (TT) antigen to stimulate in vitro anti-tetanus toxoid antibody (anti-TT) synthesis and have found that lymphocytes from many healthy elderly individuals have a reduced production of anti-TT in vitro compared to young adults. This is associated with decreased numbers of B cells secreting anti-TT IgG and a decrease in the mean amount of anti-TT IgG produced per TT-specific B cell. In the present study we report that immunization results in a significant increase in serum titers in young adults for up to one year, whereas levels in old adults fall to baseline by 6 months. The number of B cells that secrete anti-TT IgG increases after immunizations in both young and old subjects, although the number in old subjects is significantly lower than in young subjects at all times except 6 months after. The mean amount of anti-TT produced per B cell (B-cell potency) is significantly lower for the old adults both before and at 6 and 12 months after booster. Immunization does not significantly change the mean amount of anti-TT produced per B cell for either age group. The decreased response to immunization with aging is associated with decreased numbers of specific Ab- secreting B cells and usually decreased potency of those B cells.
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