Mechanism of action of a cytotonic enterotoxin produced by Aeromonas hydrophila

In this study, we describe the mechanism of action of a cytotonic enterotoxin produced by two isolates of Aeromonas hydrophila. Isolates SSU and Ah65 are of different origin and both are capable of producing either a cytotoxic enterotoxin or aerolysin. A cytotonic enterotoxin produced by diarrheal isolate SSU, which was purified and characterized in our laboratory, elevated intracellular cAMP and PgE2 levels in cultured Chinese hamster ovary (CHO) cells. Likewise, enterotoxic activity expressed by a cytotonic enterotoxin was detected in the culture filtrate of a fish isolate (Ah65) after cytotoxic activity was neutralized with homologous aerolysin monoclonal antibodies. This cytotonic enterotoxin also elevated intracellular cAMP and PgE2 levels in CHO cells, suggesting a cholera toxin-like mechanism of action for Aeromonas cytotonic enterotoxins.     

Drosophila melanogaster chemosensory and muscle development: Identification and properties of a novel allele ofscalloped and of a new locus, SG18.1, in a Gal4 enhancer trap screen

Our primary interest is to probe into the genetic and molecular mechanisms underlying the development of the chemosensory and neuromuscular systems inDrosophila melanogaster. We have generated and characterized 40 Gal4 enhancer trap lines with P-Gal4 insertion as an attempt to identify genes with a likely role in the development and differentiation of chemosensory and neuromuscular tissues, and at the same time to obtain Gal4 drivers that would facilitate targeted ectopic expression of genes in these tissues. Insertion strain SG18.1 has reporter gene activity in major olfactory components of the adult fly and in their presumptive areas in the imaginal discs. SG29.1 has an insertion in thescalloped gene and has been useful in understanding genetic interactions that pattern the wing and in defining the role ofscalloped in muscle development in flies.     

Effects of vitamin A deficiency on cell proliferation and morphology of trachea of the hamster

Abstract. Regulation by vitamin A of cell proliferation and differentiation of epithelial tissues is well-established. Deficiency of vitamin A in experimental animals leads to the development of hyperplasia and squamous metaplasia. The objective of the present study was to examine, for young hamsters, the effects of variable levels of the vitamin in the liver and trachea, on cell proliferation and morphology of tracheal epithelium and on body weights. Newly born litters were maintained on vitamin A-supplemented and vitamin A-deficient diets, and various parameters were examined at different ages. Retinol and retinyl palmitate levels were determined by high performance liquid chromatography. For animals on the supplemented diet, concentrations of liver retinyl palmitate and retinol increased progressively with age, reaching highest levels of approximately 84 and 1 -9 μg/g liver, respectively, at 28 d. In contrast, in animals on the vitamin A-deficient diet, the retinyl palmitate and retinol levels decreased progressively, reaching the lowest levels of approximately 0–32 and 0–09 μg/g, respectively. No significant reduction in retinol was observed in the trachea of animals maintained on the deficient diet for at least 20 d; their tracheas were depleted of retinol at 28 d. No vitamin A-associated differences were, however, observed in the labelling indices, growth fraction or in the morphology of the tracheal epithelium. Both the control and vitamin A-deficient animals gained weight progressively until 36 d of age, although the weight of animals in the latter group remained below those in the former group. These results show that mild-to-severe deficiency of vitamin A had no effects on cell proliferation or tracheal morphology of the hamster. The hyperplasia and squamous metaplasia in the trachea occurs only at an extreme vitamin A-deficiency when the tissue levels of the vitamin are depleted.     

Fiberoptic Bronchoscopy in Diagnosis of Opportunistic Lung Infections: Assessment of Sputa,Washings, Brushings and Biopsy Specimens

Fiberoptic bronchoscopy (washings, brushings and biopsies) was done in 25 cases of proven opportunistic pulmonary infections in compromised hosts. Diagnostic yields of bronchoscopic procedures and expectorated sputum were compared. Sputum examination gave the lowest yield (14 percent). Bronchial washings and brushings were diagnostic in 30 percent and 38 percent of patients, respectively. On transbronchial biopsy of the lung (TBB) pathogens were identified in 75 percent of patients with Pneumocystis carinii infection and 67 percent of patients with other opportunistic infections. The overall TBB yield of 73 percent was superior (P<0.05) to that of either washings or brushings. The yield from combining washings and brushings was greater than from either procedure alone, but combination with TBB did not result in any significant improvement. TBB is recommended as a useful diagnostic procedure in patients with suspected opportunistic pulmonary infections. Morbidity was minimal with this procedure, and the need for thoracotomy was reduced when it was used.     

Glutathione contributes to plant defence against parasitic cyst nematodes

Cyst nematodes (CNs) are an important group of root-infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l -γ-glutamyl-l -cysteinyl-glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate–cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione-deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione-mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine-tuning the balance between the cellular redox environment and the production of compounds related to defence against infection.     

Viral adaptation to host immune responses occurs in chronic hepatitis B virus (HBV) infection, and adaptation is greatest in HBV e antigen-negative disease

Hepatitis B virus (HBV)-specific T-cell responses are important in the natural history of HBV infection. The number of known HBV-specific T-cell epitopes is limited, and it is not clear whether viral evolution occurs in chronic HBV infection. We aimed to identify novel HBV T-cell epitopes by examining the relationship between HBV sequence variation and the human leukocyte antigen (HLA) type in a large prospective clinic-based cohort of Asian patients with chronic HBV infection recruited in Australia and China (n = 119). High-resolution 4-digit HLA class I and II typing and full-length HBV sequencing were undertaken for treatment-naïve individuals (52% with genotype B, 48% with genotype C, 63% HBV e antigen [HBeAg] positive). Statistically significant associations between HLA types and HBV sequence variation were identified (n = 49) at 41 sites in the HBV genome. Using prediction programs, we determined scores for binding between peptides containing these polymorphisms and associated HLA types. Among the regions that could be tested, HLA binding was predicted for 14/18 (78%). We identified several HLA-associated polymorphisms involving likely known anchor residues that resulted in altered predicted binding scores. Some HLA-associated polymorphisms fell within known T-cell epitopes with matching HLA restriction. Enhanced viral adaptation (defined as the presence of the relevant HLA and the escaped amino acid) was independently associated with HBeAg-negative disease (P = 0.003). Thus, HBV appears to be under immune pressure in chronic HBV infection, particularly in HBeAg-negative disease.