Immune modulation by fish kinetoplastid parasites : a role for nitric oxide

Trypanoplasma borreli and Trypanosoma carassii are kinetoplastid parasites infecting cyprinid fish. We investigated the role of nitric oxide (NO) in immune modulation during T. borreli and T. carassii infection of carp. Phagocytic cells from different organs produced NO and serum nitrate levels increased, demonstrating that T. borreli activates NO production in vivo. In contrast, T. carassii did not induce NO production in vivo and inhibited LPS-induced NO production in vitro. Production of NO was detrimental to the host as T. borreli-infected carp treated with the inducible NO synthase inhibitor aminoguanidine had a higher survival than infected control carp. This detrimental effect can be explained (in part) by the toxicity of NO to cells in vitro as NO inhibited the proliferative response of blood and spleen leukocytes. Head-kidney phagocytes were resistant to the immunosuppressive effects of NO in vitro. The NO-inducing activity of T. borreli may be an adaptation developed to ensure survival and immune evasion in the fish host. Apparently, T. carassii has adopted another strategy by deactivating specific functions of phagocytes. Both strategies may ensure long-term survival of the parasite

Binding of small molecules to lipoamide dehydrogenase

The existence of a monomer-dimer equilibrium with lipoamide dehydrogenase is demonstrated. The equilibrium can be shifted to the monomer side at low ionic strength and low pH by removing the phosphate ions by extensive dialysis. At low ionic strength, I : 0.01 and 0.02, the enzyme precipitates while aggregation takes place. This aggregation seems to be due to changes in the activity coefficient of the enzyme. High phosphate concentrations, NADI and high temperatures favor association. Also bringing the enzyme in a more polar environment causes dissociation. Dioxan and 2-chloroethanol are used to decrease the dielectric constant of the buffer solution. Inactivation and dissociation of the enzyme is time- dependent in these solutions. High concentrations of dioxan and 2-chloroethanol cause denaturation and precipitation of the enzyme. High phosphate concentrations stimulate the denaturation and precipitation of the enzyme in dioxan and 2-chloroethanol.Dissociation of the enzyme is accompanied by loss in activity and decrease in apparent α-helix content. ORD and CD data show this decrease, however the possibility that this decrease is due to changes in shape and size of the protein molecule cannot be excluded. Fluorescence and CD experiments show that upon dissociation an amino acid, a tryptophan residue, moves to a more polar environment. Also by treating the enzyme with dioxan a tryptophan residue is pertubed.Dissociation of the enzyme can also be achieved by treating the enzyme with sodium dodecylsulfate. Hydrophobic and ionic interactions are observed. Binding to the hydrophobic sites, by sodium dodecylsulfate or Tween 80, has no influence on the lipoate activity and on absorption spectrum of the enzyme in the visible- region. Binding to the ionic sites causes loss in lipoate activity and affects the absorption spectrum. From the dependency on the pH and the ionic strength it is concluded that a group of the kind BH += B + H +with a pK value around 6.6 is involved. At high SDS concentrations the binding of FAD to the enzyme is weakened and upon standing for long times the flavin dissociated off.Dimerization of the enzyme is favored by NAD +. Binding of NAD +to the enzyme yields a difference spectrum. From these spectral titration curves two pairs of NAD +-binding sites are calculated, the binding site with the highest affinity, K diss = 35 μM is assigned to the regulatory site while the binding site with K diss = 90-110 μM is assigned to the catalytic site. Upon NAD +binding to the regulatory site one proton per FAD is liberated. Comparision of the pH activity curves with computer models shows that the activating effect of NAD +in the lipoate activity can be explained by a shift in pK value of a group from pH 6.4-6.3 to 5.0-4.9 upon NAD +binding. Together with observations in the literature these results suggest that the pK value of a SH-group is shifted to lower pH upon NAD +binding. This SH-group is suggested to be functional in the S -state in the active center

Are Minerals Costing More?

This is a working paper in a continuing project "Mineral Scarcity and Economic Change", partially supported at IIASA by the U.S. National Academy of Sciences. In the present paper evidence is given on trends in relative cost to obtain minerals, for selected regions and countries. On this basis the question of increasing economic scarcity of minerals is addressed, and attention is given to the underlying forces that affect mineral cost trends. The data that are used are from an IIASA data base that covers about 50 mineral price series and economic variables on 45 countries. However, in this paper we focus primarily on Western European countries for the period 1950-1979. Since the data effort finished in summer 1980, the second oil price boom is not fully reflected

T cells and the humoral immune system

Lymphoid cells and macrophages play an important role in the development and rnaintance of humoral and cellular immunity in mammals. The lymphoid cells in the peripheral lymphoid organs are divided into two major classes: (1) thymus-derived lymphocytes or T cells and (2) bursa-equivalent-derived lymphocytes or B cells. Humoral immune responses to most antigens require interaction between macrophages, T cells and B cells. Antigen-stimulated T cells do not produce antibodies but secrete regulatory substances which have a stimulating or a suppressive effect on the differentiation of antigenstimulated B cells into antibody-producing plasma cells. The macrophage plays an important role in this T-B interaction by concentrating the antigen by endocytosis and presenting a part of it in a persisting immunogenic form on its cell membrane. Several aspects of the regulatory influence of the T cell on the humoral (B) immune system were investigated in our laboratory and the results of our experiments are presented in the papers added to this thesis

Antibiotica, een vloek of een zegen?

In Aquacultuur 2010, nr. 5 stond op pagina 33 van het artikel "Aan tafel bij Sietze Leenstra" de opmerking, dat antibiotica het immuunsysteem verstoren. Hier is wel iets voor te zeggen, maar toch moeten we oppassen, dat we niet alle antibiotica op één hoop smijten. Volgens de auteur is het vooral het gebruik van oxytetracycline in de aquacultuur, waar we een vraagteken bij moeten plaatsen