Comparative genomics and host resistance against infectious diseases.
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The large size and complexity of the human genome have limited the identification and functional characterization of components of the innate immune system that play a critical role in front-line defense against invading microorganisms. However, advances in genome analysis (including the development of comprehensive sets of informative genetic markers, improved physical mapping methods, and novel techniques for transcript identification) have reduced the obstacles to discovery of novel host resistance genes. Study of the genomic organization and content of widely divergent vertebrate species has shown a remarkable degree of evolutionary conservation and enables meaningful cross-species comparison and analysis of newly discovered genes. Application of comparative genomics to host resistance will rapidly expand our understanding of human immune defense by facilitating the translation of knowledge acquired through the study of model organisms. We review the rationale and resources for comparative genomic analysis and describe three examples of host resistance genes successfully identified by this approach. (+info)
Defective CTLA-4 cycling pathway in Chediak-Higashi syndrome: a possible mechanism for deregulation of T lymphocyte activation.
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Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4, also known as CD152) has been shown to play a major role in the regulation of T cell activation. Its membrane expression is highly regulated by endocytosis and trafficking through the secretory lysosome pathway. Chediak-Higashi syndrome (CHS) is an inherited disorder caused by mutations in the lysosomal trafficking regulator gene, LYST. It results in defective membrane targeting of the proteins present in secretory lysosomes, and it is associated with a variety of features, including a lymphoproliferative syndrome with hemophagocytosis. The murine equivalent of CHS, beige mice, present similar characteristics but do not develop the lymphoproliferative syndrome. We show herein that CTLA-4 is present in enlarged, abnormal vesicles in CHS T cells and is not properly expressed at the cell surface after T cell activation, whereas its surface expression is not impaired. It is therefore proposed that the defective surface expression of CTLA-4 by CHS T cells is involved in the generation of lymphoproliferative disease. This observation may provide insight into the role of CTLA-4 in humans. (+info)
Chediak-Higashi syndrome associated with maternal uniparental isodisomy of chromosome 1.
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Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder (incidence around 1 in 106 births), characterised by a complex immunologic defects, reduced pigmentation, and presence of giant granules in many different cell types. It most likely results from defective organellar trafficking or protein sorting. The causative gene (LYST) has recently been identified and shown to be homologous to the beige locus in the mouse. CHS has always been reported associated with premature-termination-codon mutations in both alleles of LYST. We report a unique patient with CHS, who was homozygous for a stop codon in the LYST gene on chromosome 1 and who had a normal 46,XY karyotype. The mother was found to be a carrier of the mutation, whereas the father had two normal LYST alleles. Non-paternity was excluded by the analysis of microsatellite markers from different chromosomes. The results of 13 informative microsatellite markers spanning the entire chromosome 1 revealed that the proband had a maternal isodisomy of chromosome 1 encompassing the LYST mutation. The proband's clinical presentation also confirms the absence of imprinted genes on chromosome 1. (+info)
Cytolytic mechanisms involved in non-MHC-restricted cytotoxicity in Chediak-Higashi syndrome.
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To determine the mechanisms responsible for the impaired lymphocyte-mediated cytotoxicity in Chediak-Higashi syndrome (CHS), we investigated the killing ability of peripheral blood lymphocytes (PBL) from three patients with CHS using several kinds of target cells that were sensitive to perforin, Fas ligand (FasL), and/or tumour necrosis factor-alpha (TNF-alpha). Freshly isolated CHS PBL did not kill K562 target cells, killing of which by normal PBL was perforin-dependent, as demonstrated by complete inhibition by concanamycin A (CMA), an inhibitor of perforin-based cytotoxicity. In contrast, the CHS PBL exhibited substantial cytotoxicity against Jurkat cells, which was only partially inhibited by CMA treatment but not by the addition of neutralizing anti-FasL or anti-TNF-alpha antibodies. IL-2-activated CHS PBL exhibited substantial levels of cytotoxicity against K562 and Jurkat cells, the levels being 74% and 83% of the respective normal control values, respectively. CMA treatment showed that while the cytotoxicity of IL-2-activated CHS PBL against K562 was largely dependent on perforin, that against Jurkat was largely not. IL-2-activated CHS PBL expressed FasL mRNA, and killed Fas transfectants. These findings indicate that CHS PBL have an ability to kill some target cells via a perforin-mediated pathway, especially when they are activated by IL-2. It was also demonstrated that CHS PBL can exert cytotoxicity against certain target cells by utilizing FasL and an undefined effector molecule other than perforin, FasL, or TNF-alpha. (+info)
Protein truncation test of LYST reveals heterogenous mutations in patients with Chediak-Higashi syndrome.
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Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder in which an immune deficiency occurs in association with pigmentation abnormalities. Most patients who do not undergo bone marrow transplantation die of a lymphoproliferative syndrome, though some patients with CHS have a relatively milder clinical course of the disease. The large size of the LYST gene, defective in CHS, has made it difficult to screen for mutations in a large number of patients. Only 8 mutations have been identified so far, and all lead to a truncated LYST protein. We conducted protein truncation tests on this gene in 8 patients with CHS. Different LYST mutations were identified in all subjects through this approach, strengthening the observation of a high frequency of truncated LYST proteins as the genetic cause of CHS. (+info)
The Chediak-Higashi syndrome: quantitation of a deficiency in maximal bactericidal capacity.
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The maximum bactericidal capacity of neutrophils from a patient with the Chediak-Higashi syndrome (CHS) was measured by a quantitative assay in which the neutrophils were challenged with increasing multiples of Staphylococcus aureus, 502A. At various bacterial challenges from 0.5 to 65 bacteria per neutrophil, the CHS cells killed normal numbers of bacteria in 60 minutes. However, at higher ratios with a mean of 118 bacteria per neutrophil, the percentage of bacteria killed in 60 minutes by CHS neutrophils (8.1 +/- 2.3%) was significantly less (P < 0.001) than that killed by normal neutrophils (44 +/- 2.3%). The CHS neutrophils lagged in their ability to kill low challenges of bacteria (0.5 or 1.2 bacteria per neutrophil) only at 20 minutes. A hydrogen-peroxide-producing strain of Streptococcus faecalis was killed normally by the CHS neutrophils at 60 minutes, with all ratios of challenge up to 114 to 1. Electron microscopic examination of 60-minute specimens from high ratios of challenge that were stained for myeloperoxidase activity revealed a failure of many bacteria-laden phagosomes to display this marker of degranulation. The results of this study indicate that the maximal bactericidal capacity of CHS neutrophils is saturated by a significantly lower challenge of bacteria than is required to saturate normal cells. This appears to be the result of sequestration of a significant portion of these cells' bactericidal resources in the giant granules that do not participate appreciably in degranulation. (+info)
Mapping of the beige (bg) gene on rat chromosome 17.
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The rat beige (bg) autosomal recessive gene, causing Chediak-Higashi Syndrome (CHS) in rat, was mapped on Chr 17 by using synteny of rat to mouse and humans. The linkage between the beige gene and PCR-amplified microsatellite markers in (DA-bg x BN)F1 x DA-bg backcross progeny was analysed. The recombination frequency was 9.5% between Prl and Acrm and 19.1% between Acrm and bg. The proposed order of three genes is Prl-Acrm-bg. This rat bg gene was confirmed to be homologus to the beige (bg) gene of mouse located on Chr 13 and the CHS (Lyst) gene of man located on Chr 1 (1q43). (+info)
Abnormal down-regulation of PKC is responsible for giant granule formation in fibroblasts from CHS (beige) mice--a thiol proteinase inhibitor, E-64-d, prevents giant granule formation in beige fibroblasts.
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We have previously reported that the abnormally rapid down-regulation of protein kinase C (PKC) activity is responsible for the cellular dysfunction in natural killer (NK) cells and polymorphonuclear leukocytes (PMNs) from Chediak-Higashi syndrome (beige) mice. In this report, we examined whether the down-regulation of PKC is associated with giant granule formation in fibroblasts from beige mice. In cultured beige fibroblasts, the membrane-bound PKC activity declined significantly after phorbol ester stimulation. We found that E-64-d, which is a thiol proteinase inhibitor and protects PKC from calpain-mediated proteolysis, reversed the declined PKC activity and prevented giant granule formation in beige fibroblasts. Moreover, E-64-d corrected the reduced lysosomal elastase and cathepsin G activity in beige fibroblasts. In contrast, specific PKC inhibitors, chelerythrin and calphostin C, promoted giant granule formation in normal fibroblasts. We also demonstrate that ceramide production is enhanced in beige fibroblasts and is involved in the rapid down-regulation of PKC. These results suggest that the accelerated breakdown of PKC observed in beige fibroblasts is caused by enhanced ceramide production and is also responsible for giant granule formation. (+info)