To examine pathogen-specific CD4+ and CD8+ effector T cells during infection, we restimulated splenocytes and liver cells from infected mice with an MHC class II–restricted listeriolysin O peptide (LLO190–201) and an MHC class I–restricted OVA peptide OVA257–264 (SIINFEKL), respectively. This evidence concerns the gene CD8A and infection.