ABSTRACT
Understanding immunodominance, the phenomenon of epitope-specific T cells expanding in an often distinctly hierarchical fashion, is important for the design of T-cell-based intervention strategies. Several recent studies have investigated immunodominance of H-2D
b
-restricted CD8
+
T cells specific for the nucleoprotein NP366 and acid polymerase PA224 epitopes during influenza A virus infection of C57BL/6 mice. CD8
+
T cells specific for these two epitopes are codominant during primary infection; NP366 dominates during secondary infection. While a number of explanations for this observation have been proposed, none of them can fully account for all the observed data. In this article, we use a simple mathematical model to explain the seemingly inconsistent data. We show that the dynamic interactions between CD8
+
T cells and antigen presentation lead to a situation where CD8
+
T cells are limiting during the initial response whereas antigen is limiting in the secondary response. This “numbers game” between antigen and CD8
+
T cells can reproduce the observed immunodominance of the NP336- and PA224-specific CD8
+
T cells, thereby explaining the reported experimental data.