Cross-Presentation of the Long-Lived Lymphocytic Choriomeningitis Virus Nucleoprotein Does Not Require Neosynthesis and Is Enhanced via Heat Shock Proteins

Many viral proteins that contain MHC class I-restricted peptides are long-lived, and it is elusive how they can give rise to class I epitopes. Recently, we showed that direct presentation of an epitope of the long-lived lymphocytic choriomeningitis virus nucleoprotein (LCMV-NP) required neosynthesis in accordance with the defective ribosomal products hypothesis. In this study, we report that LCMV-NP can be cross-primed in mice using either LCMV-NP-transfected human HEK293 or BALB/c-derived B8 cells as Ag donor cells. In addition, we establish that contrary to direct presentation, cross-presentation required accumulation of the mature LCMV-NP and could not be sustained by the newly synthesized LCMV-NP protein, intermediate proteasomal degradation products, or the minimal NP396 epitope. Nevertheless, NP cross-presentation was enhanced by heat shock and was blunted by inhibitors of heat shock protein 90 and gp96. We propose that cross-presentation has evolved to sustain the presentation of stable viral proteins when their neosynthesis has ceased in infected donor cells.