PERIPHERAL-BLOOD DENDRITIC CELLS REINDUCE PROLIFERATION IN IN-VITRO AGED T-CELL POPULATIONS

Dendritic cells (DC) are professional antigen presenting cells which a re essential for the initiation of an immune response. Recently we dem onstrated that DC, which had been propagated from the peripheral blood of healthy elderly people, were morphologically and functionally inta ct. It was the aim of the present study to analyze how DC from young a nd old healthy individuals could affect T cell responsiveness to antig en in an in vitro senescence model. Tetanus toroid (TT)-specific T cel l lines were derived from 3 young (< 30 years) and 3 old (> 65 years) individuals and were kept in long term culture. T cell proliferation i n response to stimulation with antigen presented by either autologous peripheral blood mononuclear cells (PBMC) or DC was assessed at three different time points, once soon after the initiation of the cultures and twice after 20 to 30 population doublings at a stage when growth w as slow and programmed cell death imminent. Antigen presentation by DC enhanced T cell proliferation at each time point and reinduced prolif eration in in vitro aged T cell populations which had stopped dividing . Terminal apoptosis was thus prevented. DC from old individuals were as effective as cells from young donors. Our results demonstrate that DC stimulate the clonal expansion and postpone the clonal elimination of antigen-specific T cell populations. As a consequence they may incr ease immunoreactivity, prolong immunological memory and be of particul ar importance for the maintenance of the T cell repertoire in old age. (C) 1997 Elsevier Science Ireland Ltd.