Limiting dilution analysis of alloreactive cytotoxic precursor cells in aging mice.

The quantitative minimal estimate of the frequency of alloantigen specific cytotoxic T lymphocyte precursor cells (CTL-p) was determined in young and old C57BL/6 mice by limiting dilution analysis. Supernatant from phorbol myristate acetate-induced EL-4 cells was used as a source of IL 2 in these assays, which therefore were independent of the presence of the Lyt-2-, IL 2-producing cells known to be deficient in aging mice. These studies showed that 24-mo-old mice had approximately 10-fold fewer CTL-p than their young counterparts. Comparison of the limiting dilution assay (LDA) with IL 2-supplemented primary MLC shows that estimates of the frequency of CTL-p do not consistently agree with cytotoxic activity detected in the higher cell density primary MLC, and that the LDA is most likely a better estimate of the effect of age on the development of CTL.