Transient normalization of lymphocyte blastogenic and specific antibody responses following boosting of healthy elderly subjects with tetanus toxoid.

The diminished in vitro blastogenic response of lymphocytes from the elderly to mitogenic stimuli is cited as evidence of immunosenescence, but the response to specific microbial antigens has not been well characterized. We measured the response to tetanus toxoid before and after boosting in young and elderly subjects. Elderly subjects (age > or = 70) and young controls (age < 35) were subjected to clinical, laboratory, and nutritional evaluation to ensure a cohort of healthy subjects. Responses of lymphocytes from the elderly to the mitogens phytohemagglutinin and concanavalin A were markedly diminished compared to those from the young. For all subjects, the average in vitro blastogenic response to tetanus toxoid of lymphocytes from elderly subjects (n = 23) was significantly diminished compared to young controls (n = 23; 31,985 +/- 4502 vs 14,411 +/- 3714 cpm, p < .01). Following boosting with tetanus in those subjects in whom boosting with tetanus toxoid was indicated, blastogenesis was comparable between elderly (n = 17) and young subjects (n = 7; 38,078 +/- 11,451 vs 42,103 +/- 9247 cpm). The boosted response to tetanus apparently was not sustained, since in the subset of subjects with a history of tetanus immunization in the past 10 years, the response of the elderly was much less than that of the young. Thus, a cohort of healthy elderly with diminished blastogenic responses to mitogens was capable of at least a transiently normal response to tetanus post boosting.

Accessory function and properties of monocytes from healthy elderly humans for T lymphocyte responses to mitogen and antigen.

The waning of cell-mediated immunity during aging has been attributed primarily to defects in T lymphocyte properties and functions. We assessed the potential contribution of accessory dysfunction of monocytes from the elderly on responses of T cells to phytohemagglutinin (PHA) and to tetanus toxoid after in vivo boosting. Accessory function of monocytes from the elderly subjects for T lymphocyte responses to tetanus toxoid was comparable to the young. Expression of the cytokines interleukin-1, interleukin-6 and tumor necrosis factor, the cell adhesion molecules ICAM-1 and LFA-3 and the class II major histocompatibility molecule HLA-DR by monocytes from the elderly and young subjects was similar. T lymphocytes from the elderly responded poorly to PHA. Monocytes from the elderly had a decreased accessory function for PHA-stimulated T cells from young, third donors. Thus, although many accessory properties of monocytes from the elderly are normal, the monocyte and T lymphocyte defects in the elderly for mitogen may represent interactive factors in cell-mediated immunity during aging.