Mechanisms of cellular invasion by intracellular parasites

Numerous disease-causing parasites must invade host cells in order to prosper. Collectively, such pathogens are responsible for a staggering amount of human sickness and death throughout the world. Leishmaniasis, Chagas disease, toxoplasmosis, and malaria are neglected diseases and therefore are linked to socio-economical and geographical factors, affecting well-over half the world’s population. Such obligate intracellular parasites have co-evolved with humans to establish a complexity of specific molecular parasite–host cell interactions, forming the basis of the parasite’s cellular tropism. They make use of such interactions to invade host cells as a means to migrate through various tissues, to evade the host immune system, and to undergo intracellular replication. These cellular migration and invasion events are absolutely essential for the completion of the lifecycles of these parasites and lead to their for disease pathogenesis. This review is an overview of the molecular mechanisms of protozoan parasite invasion of host cells and discussion of therapeutic strategies, which could be developed by targeting these invasion pathways. Specifically, we focus on four species of protozoan parasites Leishmania, Trypanosoma cruzi, Plasmodium, and Toxoplasma, which are responsible for significant morbidity and mortality.     

Polymerization of phenolic intermediates of pesticides by a fungal enzyme

Summary The fungusRhizoctonia praticola produces an extracellular phenol oxidase (laccase) which polymerizes phenolic intermediates of various pesticides. The enzyme catalyzes the formation of oligomeric products from halogenated phenolic intermediates of phenoxyalkanoate herbicides and from naphtholic products derived from carbamate insecticides. These findings permit further investigations into the mechanism and role of oxidative coupling leading to the incorporation of xenobiotic compounds into soil organic matter.     

Activity of contractile vacuole in the parasitic ciliate,Balantidium coli

Résumé Chez leBalantidium coli, la vacuole contractile se remplit graduellement et s'agrandit. Après une phase stationnaire, pendant laquelle elle reste irrégulière en apparence, elle se gonfle entièrement, devient sphérique, et puis s'affaisse subitement et expulse son contenu. L'affaissement est très rapide et ne prend qu'une fraction de seconde. Le cycle entier dure générallement 20 à 25 secondes.     

Phagocytosis of zymosan particles by mast cells

Résumé Des rats ont été injectés par voie péritonéale avec une suspension de zymosan, une préparation de parois de levure,Saccharomyces cerevisiae. Les cellules de la lymphe péritonéale furent étudiées après au microscope optique et électronique. Ces expériences ont démontré que les mastocytes changent d'aspect et que les particules de zymosan se retrouvent dans des vacuoles cytoplasmiques peu après l'injection. Les mastocytes sont donc des cellules capables de phagocytose.     

Polymerization of phenolic intermediates of pesticides by a fungal enzyme.

The fungus Rhizoctonia praticola produces an extracellular phenol oxidase (laccase) which polymerizes phenolic intermediates of various pesticides. The enzyme catalyzes the formation of oligomeric products from halogenated phenolic intermediates of phenoxyalkanoate herbicides and from naphtholic products derived from carbamate insecticides. These findings permit further investigations into the mechanism and role of oxidative coupling leading to the incorporation of xenobiotic compounds into soil organic matter.     

Methylmercury toxicity in insect: detection of mercury in lysosomes using electron microprobe]

Intoxication of Blattella by methylmercury leads to a storage of the ingested metal within the lysosomes of ileum. Mercury is always found associated with zinc, sulphur and copper. Lysosome, therefore, intervenes in a detoxication process in Insects which have been exposed to organic mercury. It is suggested that mercury might be trapped by metallothionein.     

Study of neurosecretory cells ofHelix pomatia by intracellular dye injection

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Relationship between the molecular weights of pesticides and their bioconcentration factors by fish

Summary A significant positve correlation was found between the molecular weights (187–412) of 19 pesticides and their bioconcentration factors (4–37,800) in 2 fresh-water fishes; topmouth gudgeon and fathead minnows.     

On the turnover of exogenous ferritin in the cephalopod optic gland. A microprobe study

Summary X-ray energy emission spectra of iron show that horse spleen ferritin, after injection into the blood of the octopus, is taken up, accumulated and disposed of again by lysosomes of the optic gland.Part of this work is supported by the Swiss National Foundation.     

Evidence for existence of pores in intramembranous particles revealed by freeze fracturing]

In freeze-fracture replicas of membranes (plasma and intracellular) in a variety of animal cells, it is possible to detect the presence of intramembrane particles containing an electron-dense spot. The spot is interpreted as an accumulation of platinum into a cavity; the cavity could in turn correspond to a hydrophilic pore in the particle.     

Evidence of autapses in vitro by electron microscopy combined with iontophoretic intracellular injection of peroxidase

The existence of autapses, i. e. of synapses between a neuron and its own axon, is demonstrated in vitro by means of Horseradish peroxidase (HRP) iontophoretic filling, combined with electron-microscopic (EM) analysis. After the injection of one single Purkinje cell per explant (Kitten cerebellum), the ultrastructural observation (serial thin sections) reveals the presence of both pre- and post-synaptic labelled structures. Axodendritic autapses are thus illustrated and their significance is discussed in view of earlier morphological and electrophysiological data.     

Heme structure in cooperative and noncooperative hemoglobins: study by resonant Raman diffusion]

The modifications of heme sites of hemoglobin, which should occur upon apoprotein alterations (responsible for variations of oxygen affinity), have been examined by Resonnant Raman scattering. The oxygenated (R) and deoxygenated (T) shape of apoprotein do not modify the heme states. The spectral differences between these forms are essentially due to the presence or the absence of the sixth ligand.