A Mouse Is Immunized with a Single 9 Amino Acid

A mouse is immunized with a single 9 amino acid peptide derived from the influenza virus. This peptide binds to MHC class I and produces an epitope (peptide:MHC complex) recognized by a small number of naive CD8 T cells in the mouse. The peptide is mixed with CpG oligonucleotides that are ligands for TLR-9. Surprisingly, this immunization regimen generates a very poor cytotoxic CD8 effector response to targets coated with this peptide compared to immunization with a preparation of intact heat-killed influenza virus mixed with CpG oligonucleotides. The enhanced cytotoxic T cell response to the peptide observed following immunization with intact viral particles compared to the peptide alone is due to:

A) The presence of CD4 T cell epitopes in the intact virus
B) The increased production of type I interferon elicited by the intact virus
C) The presence of additional CD8 epitopes in the intact virus
D) Presentation of peptides by macrophages instead of dendritic cells
E) Up-regulation of MHC class I molecules by the intact virus