Specific humoral immunity in the elderly: in vivo and in vitro response to vaccination

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.