Passive immunization protects guinea pigs from lethal toxoplasma infection

Abstract The cellular and humoral interactions that contribute to protective immunity in toxoplasmosis were studied by adoptive transfer of selective cell populations or immune serum and its fractions into normal syngeneic strain 2 guinea pigs. The results of this study with the RH strain of Toxoplasma gondii confirm and extend the findings of previous studies by showing that the passive transfer of parasite-sensitized T cells or of immune serum from previously infected donors protected recipient guinea pigs against lethal toxoplasmosis. An additional key finding was that similar levels of complete protection against lethal infection occurred in guinea pigs receiving partially purified anti- Toxoplasma immunoglobulins or immune cells that had been enriched for B cells prior to transfer. Cells residing in the spleen, lymph nodes and peritoneal cavity, but not the thymus, were equally effective in conferring immunity to challenged recipients. In addition, cell titration experiments revealed that guinea pigs could survive T. gondii infection by infusing them with as little as 2 × 10⁷ sensitized T cells or B cells. Unlike protection mediated by T cells, protection against lethal disease occurring in the B cell recipients was associated with the formation of Toxoplasma antibodies. These findings illustrate the major role of both humoral and cell-mediated immunity in affording protection against toxoplasmosis based on a guinea pig model of the human disease.     

A survey of toxicity of cyanobacterial blooms in Lake Ladoga and adjacent water bodies

Twentyfive cyanobacterial blooms in Lake Ladoga and adjacent water bodies were studied in the summer of 1990–1992. Toxicity of the water bloom material for mice was detected in 9 cases. The maximal tolerable doses (MTD) of the material extracted from biomass varied within 3–30 mg kg^–1 mouse body weight; 50% lethal doses (LD₅₀) were within 45–125 mg kg^–1. Toxic water blooms were registered in Karelian lakes and in the Neva Bay, Gulf of Finland. Cyanobacterial samples collected on the eastern coast of Lake Ladoga proved to be non-toxic. The species identified in toxic bloom material included Anabaena circinalis, A. flos-aquae, A. lemmermannii, Anabaena sp., Aphanizomenonflos-aquae, Gloeotrichia echinulata, G. pisum, Microcystis aeruginosa and Oscillatoria sp. These data suggest that toxic forms of cyanobacteria are widespread in Karelian lakes belonging to the drainage basin of Lake Ladoga.     

Use of synthetic lethal mutants to clone and characterize a novel CTP synthetase gene in Saccharomyces cerevisiae

In the pyrimidine biosynthetic pathway, CTP synthetase catalyses the conversion of uridine 5-triphosphate (UTP) to cytidine 5-triphosphate (CTP). In the yeast Saccharomyces cerevisiae, the URA7 gene encoding this enzyme was previously shown to be nonessential for cell viability. The present paper describes the selection of synthetic lethal mutants in the CTP biosynthetic pathway that led us to clone a second gene, named URA8, which also encodes a CTP synthetase. Comparison of the predicted amino acid sequences of the products of URA7 and URA8 shows 78% identity. Deletion of the URA8 gene is viable in a haploid strain but simultaneous presence of null alleles both URA7 and URA8 is lethal. Based on the codon bias values for the two genes and the intracellular concentrations of CTP in strains deleted for one of the two genes, relative to the wild-type level, URA7 appears to be the major gene for CTP biosynthesis. Nevertheless, URA8 alone also allows yeast growth, at least under standard laboratory conditions.     

Some Biochemical Abnormalities Caused by Cypermethrin in Adults of Tribolium castaneum (Herbst.)

Biochemical effects of sub lethal doses LC₁₀ and LC₂₀ of cypermethrin were studied on some enzymes and macromolecule activities of adult beetles of Tribolium castaneum (Herbst.). Cypermethrin caused disturbances in levels of all biochemical components under study. The dose of 0.78 ppm caused abnormalities in α‐amylase and FAA by increasing their activities i.e., 45.45% and 21.97% significantly. The higher sub lethal dose of 2.62 ppm disturbed all the parameters (AcP, α‐amylase, soluble protein and FAA) except AkP, which was decreased by 93.06%. Moreover, sub lethal doses either increased or decreased the levels of all parameters non‐significantly except AkP and FAA which were effected significantly by 87.92% and 14.29% at lower and higher doses, respectively. In the present studies, cypermethrin significantly enhanced the activity of AkP in both susceptible and resistant strains of T. castaneum adult beetles while FAA contents were increased significantly in resistant strain only. The activity of α‐amylase was significantly lowered in susceptible strain only.     

An in situ assay for induced diphtheria-toxin-resistant mutants of diploid human fibroblasts

The sensitivity of diploid human fibroblasts to the cytotoxic effects of diphtheria toxin (DT) depended on the cell growth status. Exponentially growing cells treated with 10^?3-1 lethal flocculating units (LF) of DT/ml for 4 days survived with a frequency of 4 × 10^?4. However, the DT-resistant phenotype of colonies isolated under these conditions was not stable. When the growth of the cells had been arrested by confluence or deprivation of serum growth factors prior to treatment with DT (4 days, 10^?3-0.6 LF/ml), the survival decreased to 2 × 10^?6 and the resistance of isolated colonies was stable. An in situ assay for induced DT-resistant mutants was developed in order to avoid problems associated with the possible reduced viability of the mutants relative to that of wild-type cells. A reproducible and linear dose response was obtained for the induction of DT-resistant mutants by ethylnitrosourea. The mutants were induced with high frequency by this compound (e.g., 10^?3 mutants/viable cell at a 37% survival dose); complete expression of the mutant phenotype occurred after 6 generations of growth under nonselective conditions. Isolated mutant colonies showed stable resistance to DT and were cross-resistant to Pseudomonas aeruginosa exotoxin A.     

Acclimation to temperature and death at changing lethal temperatures in the freshwater fish Chalcalburnues chalcoides

1. 1.|In the freshwater fish Chalcalburnus chalcoides, an increase in the body (standard) size caused decreases in the upper LT-50 from 36.6° to 36.0°C and lower LT-50 from 6.3° to 5.3°C

2. 2.|The fish acclimated to constant temperatures between 10°C and 30°C showed reasonable heat acclimation and also reasonable cold acclimation. Thus, an increase in the acclimation temperature from 10°C to 30°C caused increases in the upper LT-50 from 34° to 36.2°C and the lower LT-50 from 1.25 to 6.5°C.

3. 3|The mean survival time — temperature curves of 10°, 20° and 30°C acclimated fish at various constant temperatures showed decreased in the survival tim ewith increasing lethal temperatures. Furthermore, an increase in the acclimation temperature causes a shift in the survival duration-temperature curve to the right, i.e., the fish become more heat resistant. Thus, the mean survival duration of 10°, 20° and 30°C acclimated fish at 35°C were 7.5, 79.6 and 530 minutes, respectively.

4. 4.|The effect of the thermal experience to changing lethal temperatures depends on the first lethal temperature to which the fish were exposed as well as the sequence of temperature changes. In the experiments in which the first lethal temperatures were between 32° and 34°C and the temperature was varied in an ascending order, their thermal resistance was increased and the fish required 114 to 174% of the expected lethal doses to die while in the experiments in which the starting temperature were between 38° and 40°C and the temperature varied in descending order, the fish become more sensitive to the upper lethal temperature and they died after receiving only 62 to 81% of the expected lethal doses. Thus, with a gradual increase in the lethal temperature, the fish show additional acclimation in the zone of resistance which in turn causes an increase in the thermal resistance. This may have ecological significance in nature.

Comparative effects of adenine analogs upon metabolic cooperation between Chinese hamster cells with different levels of adenine phosphoribosyltransferase activity

Colony formation by variant Chinese hamster cells highly resistant to adenine analogs and deficient in adenine phosphoribosyltransferase (APRT) activity was measured after co-cultivation with APRT⁺, CHO-K1 cells in medium containing one of three different adenine analogs. Depending upon the density of APRT⁺ cells and the specific adenine analog, large differences in the recovery of APRT^? colonies were observed. The particular adenine analog and APRT⁺ cell density were more significant factors in the recovery of APRT^? colonies than the concentration of the analog or the level of APRT activity. The number of wild-type cells (CHO-K1) required to inhibit formation of APRT^? colonies by 50% (mean lethal density; MLD₅₀) with 65 μg/ml 8-aza-adenine (AzA) as the selective drug was 8.0 × 10⁵ cells/100 mm dish (1.5 × 10⁴/cm²). With 100 μg/ml 2,6-diaminopurine (DAP) the MLD₅₀ for CHO-K1 was 4.0 × 10⁵ cells/100 mm dish (7.3 × 10³/cm²). The MLD₅₀ for CHO-K1 when the DAP concentration was decreased to 50 μg/ml was only slightly higher, 5 × 10⁵ cells/100 mm dish (9.1 × 10³/cm²). The most toxic effect was observed with 2-fluoroadenine (FA). The MLD₅₀ for CHO-K1 in 2 μg/ml FA was 4.5 × 10⁴ cells/100 mm dish (8.2 × 10²/cm²), a cell density which permits minimal direct contact between APRT⁺ and APRT^? cells. The toxic effects of FA on individually resistant, APRT^? cells were found to be mediated by metabolites released into the medium by dying APRT⁺ cells. This metabolite toxicity to APRT^? cells was also demonstrated in mixtures with cells having only 8% of wild-type APRT activity. The MLD₅₀ for these APRT⁺ (8%) cells in 2 μg/ml FA was 7.5 × 10⁴ cells/100 dish (1.4 × 10³/cm²), a small difference from the MLD₅₀ for cells with wild-type levels of APRT activity. The differences in the recovery of APRT^? colonies from mixtures with APRT⁺ cells in these three adenine analogs are critical to the design of procedures for the selection of APRT^? cells from populations of APRT⁺ cells and emphasize the importance of establishing the parameters of metabolic cooperation, not only in terms of cell density but also with regard to the particular selective agent, in any experiment designed to determine precise mutation rates or to test putative mutagens upon mammalian cells in culture.     

A common sequence in the inverted terminal repetitions of human and avian adenoviruses

The termini of the avian chick embryo lethal orphan (CELO) virus DNA have been sequenced. The results revealed a 63-bp-long inverted terminal repetition (ITR) which shared the sequence ATAATA with all adenovirus termini, thus far analyzed. The CELO virus ITR differed from those of the mammalian adenoviruses in two major aspects: (i) it is not a perfect duplication; (ii) it begins with a 5'-guanylic acid residue instead of the cytidylic acid normally observed in adenoviruses.