While in vitro observations suggest that cross-presentation of antigens is mediated primarily by CD8α + dendritic cells, in vivo analysis has been hampered by the lack of systems that selectively eliminate this cell lineage. Here we show that deletion of the transcription factor Batf3 ablated development of CD8α + dendritic cells, allowing us to examine their role in immunity in vivo. Dendritic cells from Batf3 -/-mice were defective in cross-presentation and Batf3 -/-mice lacked virusspecific CD8 + T cell responses to West Nile virus. Importantly, rejection of highly immunogenic syngeneic tumors was impaired in Batf3 -/-mice. These results suggest an important role for CD8α + dendritic cells and cross-presentation in responses to viruses and in tumor rejection.During antigen 'cross-presentation' (1), antigens generated in one cell are presented by MHC class I molecules of a second cell. It remains unclear whether all antigen presenting cells (APCs) use cross-presentation and whether this pathway plays a role in immune responses in vivo (2). Dendritic cells (DCs) are a heterogeneous group of APCs with two major subsets, plasmacytoid dendritic cells (pDCs) and conventional CD11c + dendritic cells (cDCs) (3). Subsets of cDCs include CD8α + , CD4 + , and CD8α -CD4 -populations that may exert distinct functions in immune responses. Evidence has suggested that CD8α + cDCs are important for cross-presentation during infections, but is based on ex vivo analysis (4-6) or in vitro antigen loading (7). Evidence both for and against a role for cross-presentation in responses against tumors has been reported (8-10).Attempts have been made to study the in vivo role of dendritic cells by selective depletion. Diphtheria toxin treatment can deplete all CD11c hi cells in one transgenic mouse model (11), but affects splenic macrophages and activated CD8 + T cells (12). Gene targeting of transcription factors (e.g., Irf2, Irf4, Irf8, Stat3 and Id2) has caused broad defects in several DC subsets, T cells and macrophages (13). To identify genes regulating DC development, we performed global gene expression analysis across many tissues and immune cells ( fig S1A). Batf3 (p21SNFT) (14) was highly expressed in cDCs, with low to absent expression in other *To whom correspondence should be addressed. E-mail murphy@pathology.wustl.edu. fig. S1B-D).In spleens of Batf3 -/-mice we found a selective loss of CD8α + cDCs, without abnormalities in other hematopoietic cell types or architecture (Fig. 1, fig. S2-S11). CD8α + cDC coexpress DEC205, CD24, and low levels of CD11b (3,15). Batf3 -/-mice lacked splenic CD11c hi CD8α + DEC205 + cells (Fig. 1A), showed a loss of CD11c hi CD11b dull cells and CD11c hi CD8α + CD24 + cells (Fig. 1B), but had normal populations of CD4 + and CD8α -CD4 -cDC subsets (Fig. 1B). Lymph nodes and thymi of Batf3 -/-mice lacked CD8α + DCs but had normal distributions of CD8α -CD11c + cells (Fig. 1C). DEC205 int and DEC205 hi DCs were present in lymph nodes draining the skin of Batf3 -/-mice (Fig. 1C), and show...
Neutralization of flaviviruses in vivo correlates with the development of an antibody response against the viral envelope (E) protein. Previous studies demonstrated that monoclonal antibodies (MAbs) against an epitope on the lateral ridge of domain III (DIII) of the West Nile virus (WNV) E protein strongly protect against infection in animals.Based on X-ray crystallography and sequence analysis, an analogous type-specific neutralizing epitope for individual serotypes of the related flavivirus dengue virus (DENV) was hypothesized. Using yeast surface display of DIII variants, we defined contact residues of a panel of type-specific, subcomplex-specific, and cross-reactive MAbs that recognize DIII of DENV type 2 (DENV-2) and have different neutralizing potentials. Type-specific MAbs with neutralizing activity against DENV-2 localized to a sequence-unique epitope on the lateral ridge of DIII, centered at the FG loop near residues E383 and P384, analogous in position to that observed with WNV-specific strongly neutralizing MAbs. Subcomplex-specific MAbs that bound some but not all DENV serotypes and neutralized DENV-2 infection recognized an adjacent epitope centered on the connecting A strand of DIII at residues K305, K307, and K310. In contrast, several MAbs that had poor neutralizing activity against DENV-2 and cross-reacted with all DENV serotypes and other flaviviruses recognized an epitope with residues in the AB loop of DIII, a conserved region that is predicted to have limited accessibility on the mature virion. Overall, our experiments define adjacent and structurally distinct epitopes on DIII of DENV-2 which elicit type-specific, subcomplex-specific, and cross-reactive antibodies with different neutralizing potentials.Dengue fever (DF), the most prevalent arthropod-borne viral illness in humans, is caused by dengue virus (DENV). The four serotypes of DENV are transmitted to humans primarily by the mosquitoes Aedes aegypti and Aedes albopictus. DENV is a member of the Flaviviridae family and is related to the viruses that cause yellow fever and the Japanese, St. Louis, and West Nile encephalitides (8). Infection by DENV causes a spectrum of clinical disease, ranging from an acute, debilitating, selflimited febrile illness (DF) to a life-threatening hemorrhagic and capillary leak syndrome (dengue hemorrhagic fever/dengue shock syndrome). At present, no approved antiviral treatment or vaccine is available, and therapy is supportive in nature. DENV causes an estimated 25 to 100 million cases of DF and 250,000 cases of dengue hemorrhagic fever per year worldwide, with 2.5 billion people at risk for infection (27,48).DENV is an enveloped virus with a single-stranded, positivesense RNA genome (11). The 10.7-kilobase genome is translated as a single polyprotein, which is then cleaved into three structural proteins (C, prM/M, and E) and seven nonstructural (NS) proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5) by virus-and host-encoded proteases. The 500-Å DENV mature virion has a well-organized outer protein she...
West Nile virus (WNV) causes asymptomatic infection in most humans, but for undefined reasons, approximately 20% of immunocompetent individuals develop West Nile fever, a potentially debilitating febrile illness, and approximately 1% develop neuroinvasive disease syndromes. Notably, since its emergence in 1999, WNV has become the leading cause of epidemic viral encephalitis in North America. We hypothesized that CD4 + Tregs might be differentially regulated in subjects with symptomatic compared with those with asymptomatic WNV infection. Here, we show that in 32 blood donors with acute WNV infection, Tregs expanded significantly in the 3 months after index (RNA + ) donations in all subjects. Symptomatic donors exhibited lower Treg frequencies from 2 weeks through 1 year after index donation yet did not show differences in systemic T cell or generalized inflammatory responses. In parallel prospective experimental studies, symptomatic WNV-infected mice also developed lower Treg frequencies compared with asymptomatic mice at 2 weeks after infection. Moreover, Treg-deficient mice developed lethal WNV infection at a higher rate than controls. Together, these results suggest that higher levels of peripheral Tregs after infection protect against severe WNV disease in immunocompetent animals and humans.
Memory B cells have the unique capacity to recognize variants of West Nile virus, likely providing protection against mutant viruses that escape antibody neutralization.
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