ANTI-CD3-INDUCED APOPTOSIS IN T-CELLS FROM YOUNG AND OLD MICE

Light scatter measurements using now cytometry indicated that T cells from young and old mice undergo apoptosis following activation with im mobilized anti-CD3. The percentage of cells in apoptosis after 20 h ac tivation was significantly greater (p < .001) in cultures containing c ells from older animals, The mean percentages of apoptotic T cells fro m young and old mice after 20 h activation were 19.3% and 33.0%, respe ctively. The proportion of viable cells after 20 h activation was sign ificantly higher (p <.003) in the young (mean = 78.4%) than in the old animals (mean = 65.8%), Simultaneous measurements of Light scatter an d fluorescence indicated that apoptotic T cells contained both the CD4 (+) and the CD8(+) T-cell phenotypes. The frequency of apoptotic CD8() T cells was elevated (p <.007) in older animals, where the mean perc entage was 15.1%, compared to 5.3% in the young. The most dramatic dif ference between young and old (P <.0008) was seen in the percentages o f viable CD4(+) T cells after 20 h activation. The mean viable CD4(+) T-cell percentage was 33.7% in the young and 21.4% in the old, CD4(+) cells expressing high levels of CD45RB (CD45RB(hi)) after activation f or 20 h possessed light scatter and bright fluorescence properties cha racteristic of viable cells, whereas CD4(+)/CD45RB(lo) density cells c ould be identified as apoptotic based on their decreased CD4 fluoresce nce and scatter characteristics. CD4(+) cells from young animals were predominantly CD45RB(hi), whereas CD4(+) cells from the old had greate r levels of CD454RB(lo) cells. In addition to light scatter changes, m easurement of DNA content after 40 h activation revealed the presence of a sub-G, DNA apoptotic peak and a viable cell cycle distribution. A fter 40 h of activation, there was an increase in the percentage of ap optotic cells in both young and old mice, with the greatest increase s een in the cells from older animals. Further evidence supporting the p rocess of apoptosis in 40 h-activated cells was confirmed by the appea rance of DNA strand breaks detected by in situ nick translation. (C) 1 995 Wiley-Liss, Inc.