Major histocompatibility class I molecules display tens of thousands of peptides on the cell surface for immune surveillance by T cells. The peptide repertoire represents virtually all cellular translation products, and can thus reveal a foreign presence inside the cell. These peptides are derived from not only conventional but also cryptic translational reading frames, including some without conventional AUG codons. To define the mechanism that generates these cryptic peptides, we used T cells as probes to analyze the peptides generated in transfected cells. We found that when CUG acts as an alternate initiation codon, it can be decoded as leucine rather than the expected methionine residue. The leucine start does not depend on an internal ribosome entry site–like mRNA structure, and its efficiency is enhanced by the Kozak nucleotide context. Furthermore, ribosomes scan 5′ to 3′ specifically for the CUG initiation codon in a eukaryotic translation initiation factor 2–independent manner. Because eukaryotic translation initiation factor 2 is frequently targeted to inhibit protein synthesis, this novel translation mechanism allows stressed cells to display antigenic peptides. This initiation mechanism could also be used at non-AUG initiation codons often found in viral transcripts as well as in a growing list of cellular genes.

Listeria monocytogenes is a facultative intracellular pathogen capable of inducing a robust cell-mediated immune response to sub-lethal infection. The capacity of L. monocytogenes to escape from the phagosome and enter the host cell cytosol is paramount for the induction of long-lived CD8 T cell–mediated protective immunity. Here, we show that the impaired T cell response to L. monocytogenes confined within a phagosome is not merely a consequence of inefficient antigen presentation, but is the result of direct suppression of the adaptive response. This suppression limited not only the adaptive response to vacuole-confined L. monocytogenes, but negated the response to bacteria within the cytosol. Co-infection with phagosome-confined and cytosolic L. monocytogenes prevented the generation of acquired immunity and limited expansion of antigen-specific T cells relative to the cytosolic L. monocytogenes strain alone. Bacteria confined to a phagosome suppressed the production of pro-inflammatory cytokines and led to the rapid MyD88-dependent production of IL-10. Blockade of the IL-10 receptor or the absence of MyD88 during primary infection restored protective immunity. Our studies demonstrate that the presence of microbes within a phagosome can directly impact the innate and adaptive immune response by antagonizing the signaling pathways necessary for inflammation and the generation of protective CD8 T cells.

c Long-distance host-independent virus dispersal is poorly understood, especially for viruses found in isolated ecosystems. To demonstrate a possible dispersal mechanism, we show that bacteriophage T4, archaeal virus Sulfolobus spindle-shaped virus Kamchatka, and vaccinia virus are reversibly inactivated by mineralization in silica under conditions similar to volcanic hot springs. In contrast, bacteriophage PRD1 is not silicified. Moreover, silicification provides viruses with remarkable desiccation resistance, which could allow extensive aerial dispersal.T he mechanisms and extent of virus dispersal are often unclear. Given the importance of viruses in maintaining microbial diversity and recycling nutrients on a global scale (1) and causing disease (2), understanding virus distribution is essential. However, it is not clear whether virus species are cosmopolitan (3) or display regional endemism (4-8). Interestingly, local hot spring virus dispersal can result from aerosolization by fumaroles (8), indicating at least one possible host-independent dispersal mechanism.Stratospheric winds are capable of carrying bacteria and fungi from the Sahara Desert as far as the Caribbean Sea (9, 10). However, a critically limiting factor for wind-borne virus spread is the ability of the virus to resist drying; most viruses are highly sensitive to desiccation (for examples, see references 11 to 13). However, if viruses could be reversibly coated in a protective coat in addition to their capsid, they could potentially spread very widely. Silica coating is a particularly attractive possibility, since in hot spring environments, viruses can be coated with silica (14, 15). However, the effect of silicification on virus infectivity was not known. Therefore, we tested both enveloped and unenveloped viruses for their susceptibility and response to silicification. Viruses tested included bacteriophage T4 (16), bacteriophage PRD1 (17), the archaeal virus Sulfolobus spindle-shaped virus Kamchatka (SSV-K) (18), and vaccinia virus (VACV) (19).Bacteriophage T4, PRD1, SSV-K, and VACV were propagated in host cell cultures using Escherichia coli B, Salmonella enterica serovar Typhimurium LT2, Sulfolobus solfataricus strain G⍜, and murine BSC-1 cells, respectively. After growth, cell debris was removed. The resulting viruses were mixed with freshly prepared pH 7.0 to 7.1 sodium metasilicate solution in either 10 mM sodium bicarbonate-5 mM magnesium chloride for bacteriophage T4, PRD1, and SSV-K or Dulbecco's phosphate-buffered saline for VACV to final silica concentrations of 0, 5, and 10 mM (0, 300, and 600 ppm). Solutions were placed in dialysis tubing in a reservoir of the same buffer and silica concentration. The bathing solution was replaced daily. Samples were withdrawn immediately and on days 1, 3, 8, and 10. The virus titer was determined in triplicate by plaque assay. On day 10, aliquots were diluted 1:10 with a 0-ppm silica solution. Plaque assays were performed with these diluted samples on days 12, 14, 16, and 20. On day 10, aliquo...