Transience of MHC Class I-restricted antigen presentation after influenza A virus infection.

Antigen expressed as MHC Class I glycoprotein (pMHCI) complexes on dendritic cells is the primary driver of CD8(+) T cell clonal expansion and differentiation. As we seek to define the molecular differences between acutely stimulated cytotoxic T lymphocyte (CTL) effectors and long-lived memory T cells, it is essential that we understand the duration of in vivo pMHCI persistence. Although infectious influenza A virus is readily cleared by mammalian hosts, that does not necessarily mean that all influenza antigen is totally eliminated. An exhaustive series of carefully controlled adoptive transfer experiments using 3 different carboxy fluorescein diacetate succinimidyl ester-labeled T cell receptor-transgenic CTL populations and a spectrum of genetically engineered and wild-type influenza A viruses provided no evidence for pMHCI persistence over the 30-60-d interval after virus challenge. Molecular profiles identified in antigen-specific T cells at this time may thus be considered to reflect established immunologic memory and not recent CTL activation from a persistent pMHCI pool.