Insights into HLA-restricted T cell responses in a novel mouse model of dengue virus infection point toward new implications for vaccine design

The frequency of dengue virus (DENV) infection has increased dramatically in the last few decades, and the lack of a vaccine has led to significant morbidity and mortality worldwide. To date, a convenient murine system to study human T cell responses to DENV has not been available. Mice transgenic for HLA are widely used to model human immune responses, and it has been shown that mouse-passaged DENV is able to replicate to significant levels in IFN-α/βR(-/-) mice. To cover a wide range of HLA phenotypes, we backcrossed IFN-α/βR(-/-) mice with HLA A*0201, A*0101, A*1101, B*0702, and DRB1*0101-transgenic mice. A DENV proteome-wide screen identified a total of 42 epitopes across all HLA-transgenic IFN-α/βR(-/-) strains tested. In contrast, only eight of these elicited responses in the corresponding IFN-α/βR(+/+) mice. We were able to identify T cell epitopes from 9 out of the 10 DENV proteins. However, the majority of responses were derived from the highly conserved nonstructural proteins NS3 and NS5. The relevance of this model is further demonstrated by the fact that most of the epitopes identified in our murine system are also recognized by PBMC from DENV-exposed human donors, and a dominance of HLA B*0702-restricted responses has been detected in both systems. Our results provide new insights into HLA-restricted T cell responses against DENV, and we describe in this study a novel murine model that allows the investigation of T cell-mediated immune mechanisms relevant to vaccine design.     

Analysis of bivariate flow karyotypes

Bivariate flow karyotype analysis is performed using data from chromosomes stained with two fluorescent dyes, typically chromomycin A3 and Hoechst-33258, and measured in a flow cytometer or cell sorter (Carrano et al.: Proceedings of the National Academy of Sciences of the United States of America 76:1382-1384, 1979; Gray et al.: Proceedings of the National Academy of Sciences of the United States of America 72:1231-1234, 1975; Langlois et al.: Proceedings of the National Academy of Sciences of the United States of America 79:7876-7880, 1982). In the resulting bivariate histogram, most chromosome types appear as individual peaks. In sorting of chromosomes to purify a specific chromosomal type, its corresponding peak in the bivariate histogram is delineated by a rectangular region which surrounds it. All events (objects) that fall within this region trigger the sorting process. In most cases, peaks for different chromosomal types overlap to some extent, and in addition there is always an underlying background due to chromosome fragments and clumps. Thus the sorted population will not be pure; it may include more than one chromosome type and will include debris. To determine the purity of a sort, i.e., the percentage of the sorted material that is of the actual chromosomal type desired, two methods of mathematical analysis have been developed. In the more general method, the bivariate data within an analysis region that includes the sort region, are fit with a series of bivariate Gaussian functions, one for each peak. In a simplified method, the data within the analysis region are transformed into a univariate distribution of either chromomycin A3 or Hoechst-33258 fluorescence. The peaks in these univariate distributions are fit with univariate Gaussian functions. In both methods the purity is determined mathematically. The results of both methods agree well with independent methods of analysis.     

Colonic H-K-ATPase beta -subunit: identification in apical membranes and regulation by dietary K depletion

P-type ATPasesrequire both - and -subunits for functionalactivity. Although an -subunit for colonic apical membraneH-K-ATPase (HKc) has been identified and studied, its -subunithas not been identified. We cloned putative -subunit rat colonicH-K-ATPase (HKc) cDNA that encodes a 279-amino-acid protein with asingle transmembrane domain and sequence homology to other rat-subunits. Northern blot analysis demonstrates that this HKc isexpressed in several rat tissues, including distal and proximal colon,and is highly expressed in testis and lung. HKc mRNA abundance is upregulated threefold compared with normal in distal colon but notproximal colon, testis, or lung of K-depleted rats. In contrast, Na-K-ATPase ₁ mRNA abundance isunaltered in distal colon of K-depleted rats. Na depletion, which alsostimulates active K absorption in distal colon, does not increaseHKc mRNA abundance. Western blot analyses using a polyclonalantibody raised to a glutathioneS-transferase-HKc fusion proteinestablished expression of a 45-kDa HKc protein in both apical andbasolateral membranes of rat distal colon, but K depletion increasedHKc protein expression only in apical membranes. Physicalassociation between HKc and HKc proteins was demonstrated byWestern blot analysis performed with HKc antibody onimmunoprecipitate of apical membranes of rat distal colon and HKcantibody. Tissue-specific upregulation of this -subunit mRNA inresponse to K depletion, localization of its protein, its upregulationby K depletion in apical membranes of distal colon, and its physicalassociation with HKc protein provide compelling evidence that HKcis the putative -subunit of colonic H-K-ATPase.     

Nitric oxide is a signaling intermediate during bicarbonate-induced stomatal closure in Pisum sativum

The role of nitric oxide (NO) during bicarbonate-induced stomatal closure was studied in the abaxial epidermis of Pisum sativum . A few experiments were done with 10 μ M ABA, for comparison. The presence of 2 m M sodium bicarbonate or 10 μ M ABA induced an increase of NO in guard cells. Elevation of NO by sodium nitroprusside induced stomatal closure and enhanced further the closure by bicarbonate. The bicarbonate induced increase in NO of guard cells, or stomatal closure was prevented partially by 2-phenyl-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide, an NO scavenger and N -nitro- l -Arg-methyl ester, an inhibitor of NO synthase (NOS). These results suggested that guard cells generated NO on exposure to bicarbonate and that NOS was involved at least partially in such NO production. Time course experiments revealed that on exposure to bicarbonate or ABA, the rise in guard cell NO production peaked within 10 min. Experiments using pharmacological compounds like wortmannin/LY294002 (phosphatidylinositol 3 kinase inhibitors), 1 H -(1,2,4)-oxadiazole-[4,3 a ]quinoxalin-1-one (guanylyl cyclase inhibitor), nicotinamide (cyclic adenosine diphosphate ribose antagonist), guanosine 5'-O-(2-thiodiphosphate) (G-protein antagonist) suggested a role of phosphatidylinositol 3-phosphate or G-proteins during bicarbonate-induced stomatal closure.     

Cutting edge: innate immunity conferred by B cells is regulated by caspase-8

Caspase-8 is an essential component of death receptor-mediated apoptosis. Along with Fas-associated death domain protein, it is also essential for T cell proliferation in response to antigenic or mitogenic stimuli. To determine whether caspase-8 is also required for B cell proliferation, we generated mice with a B cell-specific Casp8 deficiency. Unlike T cells, caspase-8 was not required for Ag receptor-driven proliferation or Ab formation. Rather, Casp8-deficient B cells failed to proliferate in response to dsRNA and LPS, ligands for TLR3 and TLR4, respectively, but responded normally to the TLR9 agonist CpG DNA. Similarly, Ab production to trinitrophenol-LPS was selectively reduced in B cell-specific Casp8-deficient mice. The activation of NF-kappaB or IFN regulatory factor 3 was found to be unaffected by the loss of caspase-8, implicating it in a novel pathway important for some forms of innate immunity mediated by B cells.