Hookworm antigens: the potential for vaccination

Hookworms rank with Ascaris as the most prevalent soil-transmitted helminths of man. Up to 1000 million people may be infected. Not all suffer the life-threatening anaemia that reflects heavy burdens of hookworms, but even mild iron-deficiency anaemia due to hookworms can lead to intellectual and growth retardation - especially among infected children. Health education, mass chemotherapy and the sanitary disposal of faeces have been the traditional mainstays of hookworm control, but more recently chemotherapy targeted only to heavily infected individuals who appear predisposed to hookworm anaemia has emerged as a realistic alternative. Ultimately, however, knowledge of the molecular immunology of hookworm infection may provide the basis for rational vaccine development. Although the evidence for acquired immunity to hookworms in man is not strong, work is now underway to identify and to characterize antigens from third and fourth larval stages and adults of Necator americanus and species of Ancylostoma (Table 1). As this article shows, the work provides real promise for improved immunodiagnosis and possible vaccination.     

Tabtoxinine-beta-Lactam Transport into Cultured Corn Cells : Uptake via an Amino Acid Transport System

Tabtoxinine-β-lactam (T-β-L), a unique amino acid, is a toxin produced by several closely related pathovars of Pseudomonas syringae. These chlorosis-inducing pathogens establish themselves in the apoplastic space of their hosts where they release the toxin. We have examined the transport of T-β-L into cultured corn (Zea mays cv Black Mexican) cells using [¹⁴C]T-β-L. The pH optimum of the uptake of the toxin was between 4.0 and 5.5 pH units. Toxin uptake was inhibited by the protonophore, carbonyl cyanide m-chlorophenyl hydrazone, and by the sulfhydryl re-agent, N-ethylmaleimide. Tabtoxinine-β-lactam transport exhibited saturation kinetics that were described by the Michaelis-Menton equation for toxin concentrations of 1 millimolar and less. However, the transport of toxin in concentrations greater than 1 millimolar was not described by Michaelis-Menten kinetics. Glutamate and alanine exhibited similar transport kinetics with a transition to non-Michaelis-Menten kinetics when the amino acid concentration exceeded 1 millimolar. Hill numbers for glutamate, alanine, and T-β-L ranged from 0.6 to 0.8. Methionine, alanine, tyrosine, glutamine, glutamate, and arginine were inhibitors of toxin transport. Alanine was a competitive inhibitor of the transport of T-β-L and of glutamate. The data are consistent with T-β-L being transported into the plant cell through an amino acid transport system.     

Biocatalysis in multi-phase reaction mixtures containing organic liquids

A wide range of enzymes and whole microbial cells will act as catalysts in reaction mixtures that contain 2 or more phases, one of which is an organic liquid (either a reactant or including water-immiscible organic solvents). These "biphasic" systems have a variety of structures, knowledge of which aids predictions about biocatalyst activity and stability. There is often a dilute aqueous solution phase (containing the biocatalyst), which may be emulsified with the organic phase, or "trapped" within catalyst particles; sometimes however there may only be traces of water adsorbed to the enzyme or cells. These reaction systems offer several advantages for industrial applications, notably the higher solubilities of many reactants of interest, and the ability of readily available hydrolytic enzymes to catalyse syntheses. The most non-polar organic liquids are least likely to inactivate biocatalysts, though many do remain active with relatively polar solvents. Modification of the biocatalyst may stabilise against inactivation, especially where this is due to direct contact with the phase interface. The mass transfer processes required in these systems remain poorly understood, particularly because the interfacial area is often unknown. Attractive continuous reactors may be operated using a packed bed of catalyst with a trapped aqueous phase.     

Poly(gamma-glutamylcysteinyl)glycine Synthesis in Datura innoxia and Binding with Cadmium : Role in Cadmium Tolerance

The effects of Cd on poly(γ-glutamylcysteinyl)glycine [(γEC)_nG] biosynthesis and formation of (γEC)_nG:Cd complexes were measured in two cell lines of Datura innoxia with differing Cd tolerance. In addition, RNA synthesis, protein synthesis, and GSH concentrations were measured during a 48 hour exposure to Cd. Exposure to 250 micromolar CdCl₂ was toxic to the sensitive line, whereas the tolerant line survived and grew in its presence. Cd-sensitive cells synthesized the same amount of (γEC)_nG as tolerant cells during an initial 24 hour exposure to 250 micromolar CdCl₂. However, rates of (γEC)_nG:Cd complex formation differed between the two cell lines with the sensitive cells forming complexes later than tolerant cells. In addition, the complexes formed by sensitive cells were of lower molecular weight than those of tolerant cells and did not bind all of the cellular Cd. Pulse-labeling of cells with l-[³⁵S]cysteine resulted in equivalent rates of incorporation into the (γEC)_nG of both cell lines during the initial 24 hours after Cd. Rates of protein and RNA synthesis were similar for both cell lines during the initial 8 hours after Cd but thereafter declined rapidly in sensitive cells. This was reflected by a decline in viability of sensitive cells. The GSH content of both cell lines declined rapidly upon exposure to Cd but was higher in sensitive cells throughout the experiment. These results show that the biosynthetic pathway for (γEC)_nG synthesis in sensitive cells is operational and that relative overproduction of (γEC)_nG is not the mechanism of Cd-tolerance in a Cd-tolerant cell line of D. innoxia. Rapid formation of (γEC)_nG:Cd complexes that bind all of the cellular Cd within 24 hours appears to correlate with tolerance in these cells.     

Effect on in Vitro Pollen Growth of an Isolated Style Glycoprotein Associated with Self-Incompatibility in Nicotiana alata

The effect on in vitro pollen tube growth of an isolated style glycoprotein (S₂-glycoprotein) associated with self-incompatibility in Nicotiana alata was investigated. Tube growth of pollen bearing the S₂-allele was inhibited, but tube growth of pollen bearing other alleles was not affected. Inhibition showed a dose response effect. The percentage of pollen grains that germinated was not significantly affected by the S₂-glycoprotein. Growth of S₂-pollen in the presence of the S₂-glycoprotein resulted in increased binding to the pollen of monoclonal antibody (PCBC3) which has a primary specificity for α-l-arabinofuranosyl residues. Growth of pollen bearing other alleles in the presence of the glycoprotein resulted in no increased binding of the antibody.     

The effect of pregnancy and foaling on intravaginal pressure in pony mares

Pressures were recorded monthly at two sites in the vagina of each of five pregnant and five nonpregnant pony mares; pressures in five mares were also recorded weekly after foaling. The developing pregnancy did not influence pressure, and after foaling the integrity of the seal formed by the caudal reproductive tract was rapidly restored.