In vivo T cell activation, in vitro defective IL-2 secretion, and response to influenza vaccination in elderly women.

IL-2 secretion in response to mitogenic stimulation, assayed in vitro, is significantly reduced in circulating T lymphocytes isolated from healthy old people, but the significance of this abnormality and how it relates to in vivo IL-2 secretion remain unclear. We found that IL-2 secretion in response to PHA plus PMA by peripheral blood T cells isolated from 10 out of 32 (31%) healthy old individuals (mean age 86 yr, range 74-97) was significantly decreased compared with results obtained in 23 younger individuals (mean age 34 yr, range 23-46). This IL-2 secretion defect in vitro was reversible after a 3-day incubation in the absence of activators. The 10 healthy old individuals who had defective IL-2 secretion in vitro also showed increased levels of serum IL-2. T cells from 22 healthy old and 22 young individuals, who had normal IL-2 secretion (geometric mean +/- log of 1 SD: 139 +/- 0.3 U/ml and 212 +/- 0.31 U/ml, respectively) in vitro, showed a remarkable transient T cell defect in IL-2 secretion (15 +/- 0.47 U/ml for the old, 54 +/- 0.28 U/ml for the young) 15 days after influenza vaccination. IL-2 secretion became normal again 30 days after vaccination. The T cell-IL-2 activity, expressed as a T cell-IL-2 activity score (calculated as the logarithm of the serum IL-2 U/ml divided by the logarithm of the IL-2 secretion U/ml, in vitro) was significantly increased in elderly non-responders after influenza vaccination (mean +/- 1 SD: 1.4 +/- 0.51) compared with elderly (0.44 +/- 0.13) and younger responders (0.3 +/- 0.2). Our data suggest that in vitro defective IL-2 secretion is a consequence of T cell activation which seems to occur in a significant proportion of healthy elderly individuals and may be clinically relevant inasmuch as it appears to prevent the normal vaccine-induced antibody response.