Platelets support a protective immune response to LCMV by preventing splenic necrosis.

Severe arenaviral infections in humans are characterized by clinical findings common to other viral hemorrhagic fevers (VHFs), including thrombocytopenia, leukopenia, skin and internal organ hemorrhages, high viral replication, splenic necrosis, and death. Host responses, rather than direct damage by the arenaviral replication, account for most of the observed pathology, but it is not known what protective roles platelets may have in each of the manifestations. To address this issue in an animal model, we compared nondepleted (100%), partially depleted (15%), and profoundly (< 2.5%) platelet depleted mice infected with the mouse arenavirus lymphocytic choriomeningitis virus (LCMV). Here, we describe that systemic bleedings and death were seen only in those animals receiving the stronger depletion treatment. Furthermore, we showed that the nonhemorrhagic but partially platelet-depleted mice were unable to control the viral replication because of generalized splenic necrosis, affecting innate and adaptive immune cells.These data suggest that, by their supportive roles in hemostasis, platelets may be preventing the severe pathology observed in human arenaviral infections.

Transient FTY720 treatment promotes immune-mediated clearance of a chronic viral infection.

For a wide variety of microbial pathogens, the outcome of the infection is indeterminate. In some individuals the microbe is cleared, but in others it establishes a chronic infection, and the factors that tip this balance are often unknown. In a widely used model of chronic viral infection, C57BL/6 mice clear the Armstrong strain of lymphocytic choriomeningitis virus (LCMV), but the clone 13 strain persists. Here we show that the Armstrong strain induces a profound lymphopenia at days 1-3 after infection, but the clone 13 strain does not. If we transiently augment lymphopenia by treating the clone-13-infected mice with the drug FTY720 at days 0-2 after infection, the mice successfully clear the infection by day 30. Clearance does not occur when CD4 T cells are absent at the time of treatment, indicating that the drug is not exerting direct antiviral effects. Notably, FTY720 treatment of an already established persistent infection also leads to viral clearance. In both models, FTY720 treatment preserves or augments LCMV-specific CD4 and CD8 T-cell responses, a result that is counter-intuitive because FTY720 is generally regarded as a new immunosuppressive agent. Because FTY720 targets host pathways that are completely evolutionarily conserved, our results may be translatable into new immunotherapies for the treatment of chronic microbial infections in humans.

Use of replication restricted recombinant vesicular stomatitis virus vectors for detection of antigen-specific T cells.

Detection of antigen-specific T cells at the single-cell level by ELISpot or flow cytometry techniques employing intracellular cytokine staining (ICS) is now an indispensable tool in many areas of immunology. When precisely mapped, optimal MHC-binding peptide epitopes are unknown, these assays use antigen in a variety of forms, including recombinant proteins, overlapping peptide sets representing one or more target protein sequences, microbial lysates, lysates of microbially-infected cells, or gene delivery vectors such as DNA expression plasmids or recombinant vaccinia or adenoviruses expressing a target protein of interest. Here we introduce replication-restricted, recombinant vesicular stomatitis virus (VSV) vectors as a safe, easy to produce, simple to use, and highly effective vector for genetic antigen delivery for the detection of human antigen-specific helper and cytotoxic T cells. To demonstrate the broad applicability of this approach, we have used these vectors to detect human T cell responses to the immunodominant pp65 antigen of human cytomegalovirus, individual segments of the yellow fever virus polyprotein, and to various influenza proteins.