Progress in molecular parasitology

Characterization of two DNA populations of Giardia lamblia

Total DNA was isolated from the parasitic protozoan Giardia lamblia and separated into two distinct populations of different densities by centrifugation through CsCl gradients containing Hoechst dye 33258. The two populations obtained were characterized by restriction enzyme analysis and nucleic acid hybridization. The less-dense population contains non-repetitive DNA and may encode mainly structural genes, such as those for alpha- and beta-tubulin. Digestion of the DNA with several restriction endonucleases showed that the denser band was composed of a 5.5 kb unit which contains the G. lamblia ribosomal RNA cistron in tandem repeated organization.

Characterization of cDNA clones coding for muscle tropomyosin of the nematode Trichostrongylus colubriformis

The host-protective antigen from detergent-solubilised extracts of the sheep intestinal helminth Trichostrongylus colubriformis has been identified as tropomyosin. Complementary DNA clones coding for T. colubriformis muscle tropomyosin have been isolated and characterised as the first step in obtaining recombinant protein to carry out more extensive vaccination trials. The clones represent an mRNA of 1544 bases, including a relatively long 5' untranslated sequence of 307 bases and a 3' non-coding region of 344 bases. The mRNA codes for a highly alpha-helical protein of 284 residues with a molecular weight of 33,000; characteristics typically observed for the muscle tropomyosins of higher organisms. The T. colubriformis protein has 58% sequence identity with rabbit and Drosophila melanogaster muscle tropomyosins, and the differences in the protein sequence are randomly distributed throughout the molecule. There is complete identity between the three sequences for the N-terminal 9 residues, the region believed to be essential for the polymerisation of tropomyosin molecules and for binding to actin and troponin.

A novel host-protective antigen from Trichostrongylus colubriformis

The detergent-soluble fraction from Trichostrongylus colubriformis third-stage larvae contained a simple set of antigens, one of which (molecular weight 41,000) induced 43-51% protection in guinea pigs following immunization. Isolation and partial amino acid sequence analysis of this protective antigen showed it was parasite tropomyosin.

Entamoeba histolytica antigens as possible vaccinogens? A short review

A few key papers which have recently been published on the characterization of amoeba antigens are reviewed. Immunofluorescence tests and immunoelectron microscopy have demonstrated the localization of certain surface antigens on axenically cultured trophozoites. Most of the surface antigens have largely been shown to elicit a humoral response. The elicitation of cellular response has not been well illustrated. The localization of a large number of antigens in cytoplasmic vacuoles and plasma membrane indicates that a greater stimulus to the host would be provided by intracellular antigens than by those located on the surface of amoeba trophozoites. In a few inoculation studies, amoeba antigens, in combination with several adjuvants, have been successfully employed for inducing protective immunity in various animal model systems. These and other results clearly demonstrate that amoeba antigens are fully capable of generating humoral and as well as CMI responses. A combination of these two effector limbs of immunity can be fully exploited through effective use of future vaccines.

Histochemical study of Sarcocystis sp. intramuscular cysts in gastrocnemius and soleus of the cat

Histochemical investigations of Sarcocystis microcysts found in two hindleg muscles of cats were carried out. Genus identification was based on the reinforced cyst membrane structure and its dimensions, the structure of the sarcocysts, and an electron microscopic survey of bradyzoite characteristics. The cyst membrane is partly contributed by the host myofiber, the characteristic histochemical features of which it retains. Materials adjacent to the limiting membrane make it appear thicker than it actually is, particularly when the PAS method as well as techniques for the demonstration of alpha-glycerophosphate dehydrogenase and ATPase activities are used. The ground substance occupying the parasitophorous vacuole is not amorphous and metabolically inert, but rather displays a fairly strong and definite ATPase activity, suggesting a trophic role in the support of metrocytes and zoites embedded therein. Cysts tend to adapt their biochemical characteristics to the particular metabolism of the muscle fibers in which they are located. All of these findings are discussed in terms of host-parasite relationships.