During the process of cross presentation, viral or tumor-derived antigens are presented to CD8+ T cells by the Batf3-dependent CD8α+/XCR1+ classical dendritic cell (cDC1). We designed a functional CRISPR screen for novel regulators of cross presentation, and identified the BEACH-domain containing protein WDFY4 as essential for cross-presentation of cell-associated antigens by cDC1. WDFY4 was not, however, required for MHC class II presentation or for cross-presentation by monocyte-derived DCs. In contrast to Batf3−/− mice, Wdfy4−/− mice have normal lymphoid and non-lymphoid cDC1 populations that produce IL-12 and protect against Toxoplasma gondii infection. However similar to Batf3−/− mice, Wdfy4−/− mice fail to prime virus- specific CD8+ T cells in vivo or induce tumor rejection, revealing a critical role for cross-presentation in anti-viral and anti-tumor immunity.

SUMMARYMxra8 is a recently described receptor for multiple alphaviruses, including Chikungunya (CHIKV), Mayaro (MAYV), Ross River (RRV), and O’nyong nyong (ONNV) viruses. To determine its role in pathogenesis, we generated mice with mutant Mxra8 alleles: an 8-nucleotide deletion that produces a truncated, soluble form (Mxra8Δ8/Δ8) and a 97-nucleotide deletion that abolishes Mxra8 expression (Mxra8Δ97/Δ97). Mxra8Δ8/Δ8 and Mxra8Δ97/Δ97 fibroblasts show reduced CHIKV infection in culture, and Mxra8Δ8/Δ8 and Mxra8Δ97/Δ97 mice have decreased infection of musculoskeletal tissues with CHIKV, MAYV, RRV, or ONNV. Less foot swelling is observed in CHIKV-infected Mxra8 mutant mice, which correlated with fewer infiltrating neutrophils and cytokines. A recombinant E2-D71A CHIKV with diminished binding to Mxra8 is attenuated in vivo in wild-type mice. Ectopic Mxra8 expression is sufficient to enhance CHIKV infection and lethality in transgenic flies. These studies establish a role for Mxra8 in the pathogenesis of multiple alphaviruses and suggest that targeting this protein may mitigate diseasein humans.

CD8 T cells are a key component of immunity to many viral infections. They achieve this through utilizing an array of effector mechanisms, but precisely which component/s are required for protection against a respiratory Orthopoxvirus infection remains unclear. Using a model of respiratory vaccinia virus (VACV) infection in mice, we could specifically determine the relative contribution of perforin, TRAIL, and IFN-γ mediated pathways in protection against virus induced morbidity and mortality. Unexpectedly, we observed that protection against death was mediated by IFN-γ without any involvement of the perforin or TRAIL-dependent pathways. IFN-γ mRNA and protein levels in the lung peaked between days 3 and 6 post infection. This enhanced response coincided with the emergence of virus-specific CD8 T cells in the lung and the cessation of weight loss. Transfer experiments indicated that CD8 T cell autonomous expression of IFN-γ restricts virus induced lung pathology, dissemination to visceral tissues, and is necessary for clearance of virus. Most significantly, we show that CD8 T cell derived IFN-γ is sufficient to protect mice in the absence of CD4 and B-lymphocytes. Thus our findings reveal a previously unappreciated mechanism by which effector CD8 T cells afford protection against a highly virulent respiratory Orthopoxvirus infection.

Abboud et al. reveal the striking and unexpected spatial organization of central- versus effector-like memory cells within the infected lung tissue and how cooperation between these two subsets contributes to host defense.

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