Age-related changes in mechanisms accounting for low levels of polyclonally induced immunoglobulin secretion in humans.

The mechanisms accounting for low levels of T-cell-dependent polyclonal IgG secretion in old and young human adults were compared. In elderly donors, in contrast to young donors, low levels of IgG secretion by unfractionated mononuclear cells (MNCs) did not correlate with functional suppressor activity of "panning"-enriched T8+ cells. Levels of IgG secretion by MNCs did not correlate either with proportions of T8+ or T4+ cells in the MNC population or with the functional helper activity of panning-enriched T4+ cells, in either old or young age groups. In young donors suppression mediated by either 2 or 5 X 10(4)T8+ cells of "low" IgG secretors (80.2 +/- 4.8 and 90.2 +/- 1.9%) was significantly greater than that induced by T8+ cells of "high" secretors (41.8 +/- 5.7 and 71.0 +/- 4.0%). Among elderly donors, suppression mediated by either 2 or 5 X 10(4)T8+ cells was reduced in both the low IgG secretion (31.9 +/- 5.3 and 52.3 +/- 7.0%) and high IgG secreting (14.9 +/- 7.2 and 46.8 +/- 5.7%) compared to the corresponding young donor subgroup. Levels of suppression mediated by 2 X 10(4)T8+ cells were suggestively lower in the high IgG secreting elderly subgroup compared to the low secreting subgroup (P less than 0.1). Our data suggest that decreased suppressor activity is a generalized occurrence in aging and that low polyclonal T-dependent MNC IgG secretion in the elderly, in contrast to young adults, cannot be attributed to high T-suppressor activity; nor does it usually reflect defective T-helper activity.