Temperature-sensitive hamster cell line with altered membrane properties

The altered properties of a concanavalin A-resistant Chinese hamster ovary cell line with obvious temperature-sensitive growth properties is described. The variant cell line, C^R-7, was shown to have a higher efficiency of colony formation than the parental wild-type population after treatment with various concentrations of concanavalin A (ConA). The variant cells had the properties of a temperature-sensitive cell line as judged by growth studies performed on solid surfaces or in suspension culture at the permissive (34 °C) and non-permissive (39 °C) temperatures; by colony efficiency determinations performed at 34 °C and 39 °C; and by the altered ability to incorporate DNA, RNA, and protein precursors into acid-precipitable material at the non-permissive temperature. Evidence for changes in the membrane properties of C^R-7 cells included: a reduced agglutinability in the presence of ConA, an altered cellular morphology on solid surfaces, an enhanced sensitivity to the toxic effects of membrane-active agents, altered and temperature-sensitive adhesiveness properties, and a reduced ability to bind labelled ConA.     

Reduced immunoglobulin G activates complement system with decreased cooperativity

Sheep erythrocytes sensitized with intact antibody or reduced and alkylated antibody were lysed by guinea-pig serum indicating that reduced and alkylated antibody bound and activated complement. Reduction of antibody caused erythrocyte lysis to exhibit pseudo-first-order kinetics, while the lysis kinetics of erythrocytes sensitized with intact antibody was sigmoidal. Analysis of erythrocyte lysis by complement according to the von Krogh equation showed that reduction of antibody diminished the von Krogh exponent $\text{n}$ from 2.8 to 1.3, while the value of $\text{K}$ remained unchanged at 0.17 (complement dilution). These observations suggested that the sole effect of the reduction of antibody inter-heavy-chain and heavy-light chain disulfide bonds was to diminish the cooperativity of antibody-complement interaction.     

Pollen–plant–climate relationships in sub-Saharan Africa

Aim  To demonstrate that incorporating the bioclimatic range of possible contributor plants leads to improved accuracy in interpreting the palaeoclimatic record of taxonomically complex pollen types.
Location  North Tropical Africa.
Methods  The geographical ranges of selected African plants were extracted from the literature and geo-referenced. These plant ranges were compared with the pollen percentages obtained from a network of surface sediments. Climate-response surfaces were graphed for each pollen taxon and each corresponding plant species.
Results  Several patterns can be identified, including taxa for which the pollen and plant distributions coincide, and others where the range limits diverge. Some pollen types display a reduced climate range compared with that of the corresponding plant species, due to low pollen production and/or dispersal. For other taxa, corresponding to high pollen producers such as pioneer taxa, pollen types display a larger climatic envelope than that of the corresponding plants. The number of species contained in a pollen taxon is an important factor, as the botanical species included in a taxon may have different geographical and climate distributions.
Main conclusions  The comparison between pollen and plant distributions is an essential step towards more precise vegetation and climate reconstructions in Africa, as it identifies taxa that have a high correspondence between pollen and plant distribution patterns. Our method is a useful tool to reassess biome reconstructions in Africa and to characterize accurately the vegetation and climate conditions at a regional scale, from pollen data.     

The response of the intestinal epithelium in B10.A mice to infection with Trichinella spiralis

Previous studies on intestinal trichinosis have dealt mainly with areas other than the intestinal epithelium. Since the epithelium is now known to be the parasite's habitat, its response to infection is important. Infection with Trichinella spiralis in immunologically slow-responding B10.A mice was associated with crypt hyperplasia and villus atrophy. With similar infection levels in both primary and challenge infections, there was no difference in the maximal degree of atrophy or hyperplasia between the 2 groups. However, challenged mice underwent these mucosal changes in about half the time. Expulsion of worms always occurred during regeneration of the intestinal epithelium suggesting that the host's defense mechanism of altering the kinetics of the epithelium was not the prime factor causing expulsion. Pulse labelling of enterocytes with [3H] thymidine showed that there was no significant increase in the relative size of the proliferation zone. This indicates that the crypt cell output was not altered by this parasite. Atrophy of the villus was analysed with respect to its 3-dimensional shape. There was a decrease in both height and width of the villus but not thickness. Thus, there is a real decrease in the size of the enterocyte population per villus. Histochemical staining of the enterocyte brush border by an alkaline phosphatase method showed that (1) hyperplastic crypts have an enlarged maturation zone and (2) the villus epithelium is composed entirely of mature cells. The distribution of the nematode population was compared to these changes in the intestine. Trichinella spiralis showed a marked anteriad (distal to proximal) migration prior to expulsion. Thus, utilizing a novel approach to study intestinal trichinosis, the response of the mucosal epithelium has been characterized.