The biology of Giardia spp.

Gardia spp. are flagellated protozoans that parasitize the small intestines of mammals, birds, reptiles, and amphibians. The infectious cysts begin excysting in the acidic environment of the stomach and become trophozoites (the vegetative form). The trophozoites attach to the intestinal mucosa through the suction generated by a ventral disk and cause diarrhea and malabsorption by mechanisms that are not well understood. Giardia spp. have a number of unique features, including a predominantly anaerobic metabolism, complete dependence on salvage of exogenous nucleotides, a limited ability to synthesize and degrade carbohydrates and lipids, and two nuclei that are equal by all criteria that have been tested. The small size and unique sequence of G. lamblia rRNA molecules have led to the proposal that Giardia is the most primitive eukaryotic organism. Three Giardia spp. have been identified by light lamblia, G. muris, and G. agilis, but electron microscopy has allowed further species to be described within the G. lamblia group, some of which have been substantiated by differences in the rDNA. Animal models and human infections have led to the conclusion that intestinal infection is controlled primarily through the humoral immune system (T-cell dependent in the mouse model). A major immunogenic cysteine-rich surface antigen is able to vary in vitro and in vivo in the course of an infection and may provide a means of evading the host immune response or perhaps a means of adapting to different intestinal environments.     

Surface heterogeneity of rat sperm during maturation

Rat sperm isolated from the caput and caudal epididymis and the vas deferens were subjected to multiple partition in aqueous two-phase systems. The technique was used to reveal heterogeneity of a sperm population with respect to particular surface properties. Sperm from all three regions gave broad distributions indicative of heterogeneous cell populations. Greatest heterogeneity was observed for cauda sperm with caput and was sperm producing similar distributions.Following multiple partition sperm from different regions of the distribution profiles were immunostained with three antibodies known to recognise maturation antigens. The results show that some antigens are acquired during epididymal transit whilst others are present throughout.The partition (surface heterogeneity) seen cannot therefore be explained solely by the distribution of the antigens recognised by 2D6, 6B2 and 3D5.     

Retroviral-mediated gene transfer of the leukocyte integrin CD18 subunit

Children with leukocyte adherence deficiency (LAD) exhibit heterogeneous defects in the leukocyte integrin CD18 subunit that prevent surface expression of functional CD11/CD18 leukocyte integrin adherence complexes. We used a retroviral vector, designated LCD18SN, to transfer the CD18 cDNA into K562 human myeloid leukemia cells and into EBV B-cells from a child with LAD. Transfer of the LCD18SN retroviral construct, which expresses the CD18 cDNA from the Moloney Murine leukemia virus (MoMLV) long terminal repeat (LTR), into K562 cells resulted in relatively high levels of CD18 mRNA and intracellular protein. Retroviral-mediated gene transfer of CD18 into LAD EBV B-cells resulted in low, but readily measurable, levels of surface expression of the CD11a/CD18 complex in these previously deficient lymphocytes. The reconstitution of surface expression of the CD11a/CD18 complex by gene transfer of the CD18 cDNA into LAD EBV B-cells indicates that this syndrome represents a candidate disorder for gene therapy.     

Genes Responsible for Size Reduction of Marine Vibrios during Starvation Are Located on the Chromosome

In a survey of 21 marine Vibrio spp., all responded to nutrient deprivation by undergoing a reduction in size (dwarfing). However, only 43% of these strains possessed one or more plasmids, suggesting that the genes responsible for dwarfing were located on the chromosome rather than on the plasmids. This conclusion was confirmed by the observation that fragmentation and subsequent size reduction occurred in three strains from which the plasmids had been removed by curing. The cured strains lost certain characteristics, such as resistance to some heavy metals and antibiotics, that were restored when the plasmids were reintroduced by either transformation or electroporation.     

Muramyl dipeptide (MDP) synergizes with interleukin 2 and interleukin 4 to stimulate, respectively, the differentiation and proliferation of B cells

The synthetic immunomodulator muramyldipeptide (MDP) can stimulate B cells. MDP, when used alone, was apparently unable to induce the differentiation or proliferation of resting B cells. In contrast, MDP appeared to synergize with a single recombinant interleukin (IL) to stimulate either their differentiation or proliferation. We used single interleukins to avoid synergistic and antagonistic effects inherent in the use of several factors. IL-2 was found to be sufficient to restore the specific immune response of resting B cells to sheep erythrocytes; MDP greatly increased the number of plaque-forming cells of such IL-2-stimulated B cells. In contrast, IL-4 and interferon-gamma (IFN-gamma), either alone or in the presence of MDP, had no effect in this differentiation assay. MDP was also able to stimulate polyclonally activated B cells. IL-4 increased the proliferation of anti-IgM-stimulated B cells, leading to enlargement and driving more cells into the cell cycle; these effects were further enhanced by MDP, more cells being induced to proliferate, to enlarge, and to progress into the cycle with a higher frequency of cells in the G1B, S, and G2/M compartments. Intracellular free calcium levels were not increased by IL-4 and/or MDP, and the two compounds did not modify the anti-IgM-induced calcium mobilization. Therefore, MDP appears to amplify cytokine effects in B cell activation, by a mechanism which does not appear to involve free calcium mobilization.     

Analysis of cellular interactions in density-dependent inhibition of 3T3 Cell proliferation

Subpopulations of different proliferative status are determined during cell-density dependent proliferation of 3T3 cells. From these data the probability of conversion of proliferative to quiescent cells is derived and found to correlate well with published data on binding of growth-inhibiting factors secreted from growth-inhibited cells.Based on material presented at the Symposium Intercellular Communication Stuttgart, September 16–17, 1982     

A simple,rapid assay for cysteamine and other thiols

Cysteamine is under investigation as an aid in radiation therapy and as a treatment for the inherited disorder cystinosis. An assay is presented for its measurement in biological fluids. The specific reaction of thiosulfonates with sulfhydryl compounds is employed to form a radiolabeled derivative of cysteamine which is then isolated by high-voltage electrophoresis on paper. Cysteamine can be measured in aqueous solutions, plasma, and urine with this method.     

Formation of human immunoreactive LMW and HMW-kininogens during coagulation. Comparison with bradykinin activity

Variations of the levels of human HMW and LMW kininogens have been studied in serum and in plasma incubated in vitro during 30 hours, at three different temperatures: 4 degrees, 22 degrees and 37 degrees C. There is a small difference between the level of LMW kininogen in plasma and in serum, but the serum and plasma level of LMW kininogen are almost stable during the time of incubation at the three temperatures. However, HMW kininogen is reduced in serum to about fifty percent of its plasma level. It decreases in plasma and in serum during incubation, overall at 4 degrees C. A strict parallelism stays between the radioimmunoassay and the bioassay.