Figure 3.

Effects of increasing age on T-cell tolerance to TAChR p146-162. Old mice were immunized once with TAChR and draining lymph node T cells were stimulated in vitro and [³H]-thymidine incorporation measured. In vitro responses to TAChR were judged as “responsive” (>2000 cpm) or “minimally responsive” (<2000 cpm) (Panel A). The TAChR stimulus used (1.9 nM for experiments B and C or 1.2 nM for experiments A and D) was within the linear range for the responses from most old mice. In three old mice, low numbers of draining lymph node cells prohibited complete in vitro analysis; these mice were labeled “senescent” (Panel A). T-cell populations from individual “responsive” old mice were used to assess reactivity to the α-chain peptide, p146-162; T cells from young immunized mice were tested in parallel (Panel B). Proliferation to 19 nM p146-162 was graphed for all animals using filled symbols; this peptide concentration was within the linear range for responses from nontransgenic mice. The upper 95% confidence limit for the mean of young transgenic responses (dashed line) and the mean value for each experiment group (solid lines) are indicated. Several mice (numbers B61, 140, 216) had enlarged spleens (> 7 mg/g body weight); they were included in Panel A for completeness. In an additional experiment (Old/IL-12 in Panel B), a more strenuous immunization protocol was used as described in Materials in Methods. Briefly, 24 month old mice were given three TAChR/CFA immunizations and were also injected with the enhancing cytokine, IL-12. The T cell responses to p146-162 for these animals are shown with open squares (Panel B).