TAP1-I- and C57BL/6 macrophages may process Crl-OVA and full-length OVA in different cellular compartments and that the protein context of the OVA Peptide(257-264) epitope influences the extent of TAP-independent processing for MHC class I presentation. OVA Peptide(257-264) epitope is presented with a differential dependence on the TAP transporter depending on the protein context of the OVA epitope: OVA Peptide(257-264) contained within the MBPCrl-OVA or Crl-OVA bacterial fusion proteins is presented with little dependence on the TAP transporter, while OVA Peptide(257-264) contained within full-length ovalbumin is largely dependent on the TAP transporter, regardless of whether recombinant OVA is expressed in bacteria or the native protein is coupled to polystyrene beads.