Characterization of TAP-independent and brefeldin A-resistant presentation of Sendai virus antigen to CD8+ cytotoxic T lymphocytes.

H-2Kb-transfected T2 cells, which lack both TAP1/2 and LMP2/7 genes, are able to efficiently process and present Sendai virus Antigen to Kb-restricted Sendai virus-specific CTL. This presentation is not inhibited by Brefeldin A (BFA). Here we extend our analysis of this novel antigen presentation pathway. We show that presentation of Sendai virus antigen was not due to sensitization of T2Kb cells by peptides in the virus preparation or peptides released from virus infected cells. Also, the ability to present Sendai virus in a BFA resistant fashion was specific for cells of the T2 lineage. Re-expression of TAP1/2 genes in T2Kb cells did not alter the capability to present antigen in a BFA resistant fashion, i.e. the presence of a functional TAP transporter complex did not relocate (all) peptides to the classical pathway for antigen processing and presentation. We found that co-infection of T2Kb cells with either Sendai virus plus influenza virus or Sendai virus plus VSV did not relocate presentation of influenza or VSV antigen to the TAP independent BFA resistant antigen presentation pathway. Peptide elution experiments and studies with peptide-specific CTL firmly demonstrated that the antigen presented by T2Kb cells after infection with Sendai virus was the natural Sendai virus epitope NP324-332. The same epitope, when expressed as a minigene in vaccinia virus, could be presented also by T2Kb cells but this presentation could be blocked by BFA. Thus, the TAP independent BFA resistant presentation of antigen seem cell (T2 lineage) and virus (Sendai virus) specific, but not epitope specific. The ability of T2Kb cells to present Sendai virus antigen in a TAP independent BFA resistant fashion was only partially blocked by lysosomal inhibitors such as methylamine, ammonium chloride and chloroquine. These findings demonstrate that TAP1/2-independent and BFA-resistant class I processing is only expressed in certain cell types, in parallel with classical MHC class I processing, and that Sendai virus selectively can enter this pathway. Hypothetical models for the TAP-independent class I processing are discussed.