Relative Frequencies of Epitope Occurrences in the Genome and CD8⁺ T-Cell Responses

<div><p>(A) Venn diagram representing relative frequencies and overlap of T cells responding to T. cruzi epitopes. The blue shaded circles (left) show the high-abundance overlapping peptides TSKB21 and TSKB20, along with the low-abundance overlapping peptide TSKB260. These peptides are among the most highly represented H-2K^b–binding peptides in the proteome and elicit the strongest CD8⁺ T-cell response following infection with Brazil strain <i>T. cruzi,</i> as shown in (B). The smaller purple shaded circles (right) show the lower-abundance epitopes TSKB18, TSKB74, TSKB80, and TSKB89, which are recognized by T-cell populations that overlap minimally with TSKB20/21/260-specific T cells.</p><p>(B) Relative frequencies of CD8⁺ T cells recognizing the TSKB20 (blue) and TSKB18 (purple) families of peptides in the acute (left) and chronic (right) phase of T. cruzi infection in mice infected with three different strains. While there are strain-dependent differences in the magnitude of the TSKB20-specific T-cell responses, these responses all follow a similar pattern of expansion and contraction during acute infection, which may be explained simply by strain-dependent differences in the rates of parasite replication and/or expression levels of TSKB20. However, T-cell responses to TSKB18 vary remarkably in both their magnitude and kinetics following infection with the various strains. Sustained expansion of TSKB18-specific T cells following infection with CL or Y strains results in different hierarchies of Ag-specific CD8⁺ T cells in chronic infection with the three different strains (right).</p>