RpoB127-135Peptide Derived from Mycobacterium tuberculosis is Processed and Presented to HLA-A*0201 Restricted CD8+ T Cells via an Alternate HLA-I Processing Pathway

Abstract

Mycobacterium tuberculosis (MTB) resides and replicates inside macrophages. In our previous report, we reported that CD8+ T cell-mediated immune responses specific for the peptide derived from MTB RNA polymerase beta-subunit (RpoB 127-135 ) could be induced in TB patients expressing HLA-A*0201 subtype. In order to examine whether RpoB127-135 specific CD8+ T cells can recognize MTB infected macrophages in vitro, CD8+ T cell lines specific for RpoB 127-135 peptide were generated from peripheral blood mononuclear cells (PBMCs) of healthy HLA-A*0201 subjects by in vitro immunization technique. In this study, we observed RpoB 127-135 specific CD8+ T cells could recognize and destroy macrophages infected with MTB for 2 to 4 days. RpoB 127-135 specific CD8+ T cell immune response was inducible from PBMC of healthy subjects expressing HLA-A*0206 subtype, one of HLA-A2 supertype members. Next, we investigated the HLA-I processing mechanism of RpoB 127-135 peptide in MTB infected macrophages. As a result, the presentation of the MTB derived epitope peptide, RpoB 127-135 , to CD8+ T cells was not inhibited by the treatment with brefeldin-A (ER-Golgi transport inhibitor) or lactacystin (proteasome inhibitor), which blocks the classical HLA-I processing pathway. However, RpoB 127-135 specific CD8+ T cell activity was blocked either by the blocking agent for the endocytosis (cytochalasin D) or by the blocking antibody (W6/32) for HLA-I molecules. Therefore, the RpoB 127-135 peptide may be processed by accessing the alternate HLA-I processing pathway. Understanding the processing and presentation mechanisms of the MTB derived proteins will help to improve the efficacy of vaccines and the efficiency of therapeutic agents for TB.