Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

Leishmania mexicana mexicana: attachment and uptake of promastigotes to and by macrophages in vitro

Promastigotes of Leishmania mexicana mexicana attach to mouse macrophages in vitro in the absence of serum by a wheat germ agglutinin-like ligand on the surface of the promastigote that binds to the N-acetyl glucosamine moiety of a receptor on the surface of the macrophage. The binding is temperature dependent, and the macrophage receptor is trypsin, cytochalasin B, and is assisted or inhibited as for attachment. Treatment of promastigotes with proteolytic enzymes uncovers a receptor for a serum component that binds strongly to a mouse macrophage receptor in vitro. The strain of mice donating the macrophages had little effect upon attachment and uptake except that A strain mouse macrophages attached fewer promastigotes in 10 min than those of outbred mice, but took up as many promastigotes over 90 min as those of outbred mice. Low responder Biozzi mouse macrophages took up more promastigotes than high responder Biozzi mouse macrophages. Normal unheated human, rabbit, and guinea pig sera lysed promastigotes and so inhibited their attachment to macrophages in vitro. Unheated immune serum showed an enhanced inhibition of attachment. Heated normal serum allowed attachment and uptake, while promastigotes treated with heated immune serum showed enhanced attachment to and uptake by macrophages. Treatment of macrophages in vitro with immune serum enhanced their ability to attach promastigotes and to engulf them. Repeated 90-min exposures of a population of promastigotes to uptake by mouse macrophages in vitro did not deplete the population of any sub-population more likely to be taken by macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of action of phorbol myristate acetate on human natural killer cell activity

We have investigated the kinetics of inhibition and regeneration of human natural killer (NK) cell-mediated lysis of K562, a human erythroleukemia cell line, by the potent tumor-promoting agent phorbol-12-myristate-13-acetate (PMA). It is shown that PMA inhibits NK cell-mediated cytotoxicity (CMC) in a dose-dependent manner whether the compound is present throughout the 4-hr cytotoxic assay or the effector cells (EC) are pretreated with PMA. Pretreatment of the target cells (TC) with PMA produced a different profile of NK activity suggesting that PMA inhibition of NK-CMC is primarily due to the inactivation of EC. PMA-induced inhibition of NK-CMC does not affect TC binding and is not circumvented by compounds that enhance intracellular levels of cyclic guanosine monophosphate (cGMP) or calcium. Furthermore, and contrary to a recent report, PMA-induced inhibition of NK-CMC is independent of monocytes. Finally, kinetic studies revealed that PMA-induced inhibition of NK-CMC occurs rapidly and is fully reversible provided that “regenerated EC” are thoroughly washed, prior to the cytotoxic assay, to rid the cell suspension of residual PMA. The potential implications of these results to the currently accepted theory of TC destruction by NK cells, the stimulus-secretion model, are discussed.     

Antiplasmodial activity of Artemisia annua plant cell cultures

Extracts of Artemisia annua cultures have been assessed for in vitro activity against the malarial parasite Plasmodium falciparum. Callus and suspension cells and medium were analysed and examined for their activity at different stages of growth and development. Time-course experiments were carried out to investigate the influence of various basal media, plant growth regulators and light on both growth and possible artemisinin production. Two active fractions were obtained but artemisinin was not detected.     

Dengue virus-specific cross-reactive CD8+ human cytotoxic T lymphocytes

Stimulation with live dengue virus of peripheral blood mononuclear cells from a dengue virus type 4-immune donor generated virus-specific, serotype-cross-reactive, CD8+, class I-restricted cytotoxic T lymphocytes (CTL) capable of lysing dengue virus-infected cells and cells pulsed with dengue virus antigens of all four serotypes. These CTL lysed autologous fibroblasts infected with vaccinia virus-dengue virus recombinant viruses containing the E gene or several nonstructural dengue virus type 4 genes. These results demonstrate that both dengue virus structural and nonstructural proteins are targets for the cytotoxic T-cell-mediated immune response to dengue virus and suggest that serotype-cross-reactive CD8+ CTL may be important mediators of viral clearance and of virus-induced immunopathology during secondary dengue virus infections.     

A review of the genus Parahemiurus Vaz & Pereira, 1930 (Digenea: Hemiuridae)

The genus Parahemiurus Vaz & Pereira, 1930 (syn.: Daniella Sahai & Srivastava, 1977) is defined, its major morphological characters discussed and a key to species given. The species P. merus (Linton, 1910) (syns: P. parahemiurus Vaz & Pereira, 1930, P. sardiniae Yamaguti, 1934, P. seriolae Yamaguti, 1934, P. platichthyi Lloyd, 1938, P. atherinae Yamaguti, 1938, P. harengulae Yamaguti, 1938, P. noblei King, 1962) and P. anchoviae Pereira & Vaz, 1930 are described. Other species recognized are P. clupeae Yamaguti, 1953, P. [originally Daniella] madrasensis (Sahai & Srivastava, 1977) n. comb. (syns: P. dussumieriai Hafeezullah, 1981, P. indicus Ahmad, 1981), P. ecuadori Manter, 1940, P. engraulisi Gupta & Jahan, 1977 (syns: P. cameroni Gupta & Ahmad, 1977, P. puriensis Ahmad, 1981, P. simhai Gupta & Gupta, 1978, P. tricanthusi Gupta & Puri, 1984) and P. yanamense Hafeezullah, 1980. Forms considered species inquirendae are P. arripidis Lebedev, 1971, P. clupeae of King (1964), P. dogieli Skrjabin & Guschanskaya, 1953, P. pseudosciaenae Shen, 1985 and P. trachichthodi Lebedev, 1968. Host and locality information is given in detail for all species. The complete life-cycle is not known, but metacercariae are reported in chaetognaths and teleosts. The definitive hosts of Parahemiurus spp. most frequently reported belong in the families Clupeidae and Carangidae and the genus is most commonly reported in temperate and subtropical waters.