Effects of age on the fine specificity of the T-cell response to TAChR. Female C57BL/6 mice 2, 12, and 20 months of age were immunized with TAChR/CFA and lymph nodes were extracted 7 days later. Single cell suspensions were stimulated with individual alpha chain peptides (p146-162, p111-126, p182-198, or p360-378) or p61-76 (a negative control). A peptide concentration toward the upper limit of the linear range for the p146-162 T-cell responses (∼142 nM) was chosen in order to enhance evidence of epitope spreading. Proliferation was measured by [3H] thymidine incorporation and expressed as the mean cpm with peptide minus the mean cpm without peptide. The experiment was repeated twice and the results summarized graphically.