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(1/2910) Natural variation of the expression of HLA and endogenous antigen modulates CTL recognition in an in vitro melanoma model.

Increasing attention has been devoted to elucidating the mechanism of lost or decreased expression of MHC or melanoma-associated antigens (MAAs), which may lead to tumor escape from immune recognition. Loss of expression of HLA class I or MAA has, as an undisputed consequence, loss of recognition by HLA class I-restricted cytotoxic T cells (CTLs). However, the relevance of down-regulation remains in question in terms of frequency of occurrence. Moreover the functional significance of epitope down-regulation, defining the relationship between MHC/epitope density and CTL interactions, is a matter of controversy, particularly with regard to whether the noted variability of expression of MHC/epitope occurs within a range likely to affect target recognition by CTLs. In this study, bulk metastatic melanoma cell lines originated from 25 HLA-A*0201 patients were analyzed for expression of HLA-A2 and MAAs. HLA-A2 expression was heterogeneous and correlated with lysis by CTLs. Sensitivity to lysis was also independently affected by the amount of ligand available for binding at concentrations of 0.001 to 1 mM. Natural expression of MAA was variable, independent from the expression of HLA-A*0201, and a significant co-factor determining recognition of melanoma targets. Thus, the naturally occurring variation in the expression of MAA and/or HLA documented by our in vitro results modulates recognition of melanoma targets and may (i) partially explain CTL-target interactions in vitro and (ii) elucidate potential mechanisms for progressive escape of tumor cells from immune recognition in vivo.  (+info)

(2/2910) Major histocompatibility complex differentiation in Sacramento River chinook salmon.

The chinook salmon of the Sacramento River, California, have been reduced to a fraction of their former abundance because of human impact and use of the river system. Here we examine the genetic variation at a major histocompatibility complex class II exon in the four Sacramento chinook salmon runs. Examination of the alleles found in these and other chinook salmon revealed nucleotide patterns consistent with selection for amino acid replacement at the putative antigen-binding sites. We found a significant amount of variation in each of the runs, including the federally endangered winter run. All of the samples were in Hardy-Weinberg proportions. A significant amount of genetic differentiation between runs was revealed by several measures of differentiation. Winter run was the most genetically divergent, while the spring, late-fall, and fall runs were less differentiated.  (+info)

(3/2910) Maturation, activation, and protection of dendritic cells induced by double-stranded RNA.

The initiation of an immune response is critically dependent on the activation of dendritic cells (DCs). This process is triggered by surface receptors specific for inflammatory cytokines or for conserved patterns characteristic of infectious agents. Here we show that human DCs are activated by influenza virus infection and by double-stranded (ds)RNA. This activation results not only in increased antigen presentation and T cell stimulatory capacity, but also in resistance to the cytopathic effect of the virus, mediated by the production of type I interferon, and upregulation of MxA. Because dsRNA stimulates both maturation and resistance, DCs can serve as altruistic antigen-presenting cells capable of sustaining viral antigen production while acquiring the capacity to trigger naive T cells and drive polarized T helper cell type 1 responses.  (+info)

(4/2910) CD45 can act as a negative regulator for the transition from early to late CD4+ CD8+ thymocytes.

The differentiation process from CD4-CD8- double-negative (DN) thymocytes to CD4+CD8+ double-positive (DP) stage is accompanied by vigorous proliferation. The resulting DP cells contain a sizable proportion of large cycling cells, but most DP cells are small resting cells. To explore the molecular mechanisms which regulate cell proliferation of DP thymocytes prior to further development, we used TCR-transgenic (Tg) mice with non-selecting MHC (Tg-Neut), which contain almost exclusively DP thymocytes that are not subject to either positive or negative selection. In Tg-Neut, the thymus contained DP cells of relatively large size, which showed higher extracellular signal-regulated kinase activity and enhanced responsiveness to mitogen compared to small DP cells. This indicates that all the large DP cells in the thymus are not positively selected and that they possess proliferative potential. When Tg-Neut mice were backcrossed with CD45 knockout mice (CD454-/- Tg-Neut), the thymus showed an increase of large DP cells and cycling cells, but a decrease of apoptotic cells. Furthermore, Bcl-2 expression and Jun N-terminal kinase activity, which are associated with resistance to apoptosis, were enhanced. These observations suggest that thymocyte proliferation in the DP stage is suppressed by a CD45-related process with regulation of mitogen-activated protein kinase and Bcl-2 unless DP cells receive TCR-mediated signals.  (+info)

(5/2910) Cellular distribution of a mixed MHC class II heterodimer between DRalpha and a chimeric DObeta chain.

Human MHC class II antigens include HLA-DR, -DQ, and -DP molecules that present antigens to CD4+ T cells, as well as the non-classical molecules HLA-DM and -DO. HLA-DM promotes peptide binding to class II molecules in endocytic compartments and HLA-DO, which is physically associated with HLA-DM in B lymphocytes, regulates HLA-DM function. Antibodies specific for the DObeta chain were obtained by immunization of mice with a heterodimer consisting of a chimeric DObeta chain (DR/DObeta), containing 18 N-terminal residues of DRbeta, paired with the DRalpha chain and isolated from transfected murine fibroblasts. The specificity of this serum for the DObeta chain and the lysosomal expression of the HLA-DO protein was confirmed using mutant human B cell lines lacking DR or DO molecules. The lysosomal localization of HLA-DO in human B cells contrasts with the cell surface expression of the mixed pair in transfected murine fibroblasts and raises questions concerning the role of the putative targeting motifs in HLA-DO. Transfection of the chimeric DR/DObeta chain along with DRalpha into human epithelial HeLa cells resulted in high levels of expression of the mixed isotypic pair at the surface of transfectants as well as in lysosomes. The same pattern was observed in HeLa cells transfected with the DObeta chimera and a DRa chain lacking the cytoplasmic tail. Taken together, these results suggest that functional sorting motifs exist in the DObeta chain but that the tight compartmentalization of HLA-DO observed inside B lymphocytes is controlled by the HLA-DOalpha chain and HLA-DM.  (+info)

(6/2910) Localization of non-Mhc collagen-induced arthritis susceptibility loci in DBA/1j mice.

One approach to understanding common human diseases is to determine the genetic defects responsible for similar diseases in animal models and place those defective genes in their corresponding biochemical pathways. Our laboratory is working with an animal model for human rheumatoid arthritis called collagen-induced arthritis (CIA). We are particularly interested in determining the location of disease-predisposing loci. To that end, we performed experiments to localize susceptibility loci for CIA in an F2 cross between the highly susceptible mouse strain DBA/1j and the highly resistant mouse strain SWR/j. Specifically, a quantitative trait locus analysis was performed to localize regions of the mouse genome responsible for susceptibility/severity to CIA. One susceptibility locus, Cia1 in the major histocompatibility locus, had been identified previously. Two additional loci were detected in our analysis that contribute to CIA severity (Cia2, Cia3) on chromosomes 2 and 6. A third locus was detected that contributes to the age of onset of the disease. This locus (Cia4) was located on chromosome 2 and was linked to the same region as Cia2. Determining the identity of these loci may provide insights into the etiology of human rheumatoid arthritis.  (+info)

(7/2910) Activation of target-tissue immune-recognition molecules by double-stranded polynucleotides.

Abnormal expression of major histocompatibility complex (MHC) class I and class II in various tissues is associated with autoimmune disease. Autoimmune responses can be triggered by viral infections or tissue injuries. We show that the ability of a virus or a tissue injury to increase MHC gene expression is duplicated by any fragment of double-stranded (ds) DNA or dsRNA introduced into the cytoplasm of nonimmune cells. Activation is sequence-independent, is induced by ds polynucleotides as small as 25 bp in length, and is not duplicated by single-stranded polynucleotides. In addition to causing abnormal MHC expression, the ds nucleic acids increase the expression of genes necessary for antigen processing and presentation: proteasome proteins (e.g., LMP2), transporters of antigen peptides; invariant chain, HLA-DM, and the costimulatory molecule B7.1. The mechanism is different from and additive to that of gamma-interferon (gammaIFN), i.e., ds polynucleotides increase class I much more than class II, whereas gammaIFN increases class II more than class I. The ds nucleic acids also induce or activate Stat1, Stat3, mitogen-activated protein kinase, NF-kappaB, the class II transactivator, RFX5, and the IFN regulatory factor 1 differently from gammaIFN. CpG residues are not responsible for this effect, and the action of the ds polynucleotides could be shown in a variety of cell types in addition to thyrocytes. We suggest that this phenomenon is a plausible mechanism that might explain how viral infection of tissues or tissue injury triggers autoimmune disease; it is potentially relevant to host immune responses induced during gene therapy.  (+info)

(8/2910) Genetic control of cytolytic T-lymphocyte responses. I. Ir gene control of the specificity of cytolytic T-lymphocyte responses to trinitrophenyl-modified syngeneic cells.

The ability of cytotoxic T lymphocytes (CTL) induced in vitro to trinitrophenyl (TNP)-modified syngeneic cells to cross-reactively lyse a TNP allogeneic spleen target varies among inbred mouse strains. The cross-reactive CTL phenotype was found to be histocompatibility 2 (H-2) linked and to be dominant in F1 hybrid mice. All strains investigated demonstrated cross-reactivity except for some strains bearing portions of the H-2k haplotype. The gene(s) controlling this response maps to the K and/or I-A region of the H-2 complex. We have termed the immune response (Ir) gene responsible for controlling the specificity of CTL induced to TNP-modified syngeneic cells Ir-X-TNP.  (+info)