Figure 6.

Robustness of ligand discrimination in the presence of receptor crosstalk. There are two sources of variability in the number of TCRs fully activated by ligand as discussed in the text. Runs of the same simulation with different random-number seeds were done to estimate the variability in numbers of TCRs that are fully activated. The results are expressed as the mean ± standard deviation of 25 experiments. There is a clear demarcation between optimal and suboptimal ligands that depends on the T cell activation threshold. For example, if the threshold for cell activation is set at a high value (e.g., 80% of TCR fully activated), the T cell can distinguish its optimal ligand from one whose k_off varies by only a factor of 3. With less stringent thresholds (e.g., 40% of TCR fully activated), the T cell may be activated with high concentrations of this ligand but never by a ligand with a k_off of 10 × k_opt.