A cluster of tularaemia after contact with a dead hare in the Netherlands.

Tularemia is thought to be rare in the Netherlands. Here we describe a cluster of two patients who contracted tularaemia after field dressing of a hare found dead. Additionally, infection from the same source is suggested in three animals.

Silencer activity of NFATc2 in the interleukin-12 receptor beta 2 proximal promoter in human T helper cells.

Interleukin 12 (IL-12) is a potent enhancer of interferon gamma production by activated T cells. The high-affinity IL-12 receptor (IL-12R) is a heterodimer of a beta1 and a beta2 subunit. Expression of the signaling IL-12Rbeta2 chain is usually low, as compared with the more abundant beta1 chain, and may be rate-limiting for IL-12 sensitivity. Little is known about the mechanisms controlling IL-12Rbeta2 gene expression. Reporter gene assays in IL-12Rbeta2-expressing Jurkat cells showed that truncation of the region from -151 to -61 abrogated promoter activity. The proximal promoter region does not contain a typical TATA box, suggesting a role for SP-1. Indeed, mutagenesis of the -63 SP-1 consensus site decreased transcription by 50%. Electrophoretic mobility shift experiments confirmed the binding of SP-1 and SP-3 at this site. In contrast, truncation of -252 to -192 increased promoter activity. Likewise, mutagenesis of the consensus nuclear factor of activated T cells site at -206 increased promoter activity by 70%, suggesting silencer activity of this element. Electrophoretic mobility shift experiments with primary Th (T helper) cells showed the formation of a specific, T-cell receptor-inducible complex at this site that is sensitive to cyclosporin A and supershifted with anti-NFATc2 in both Th1 and Th2 cells. Accordingly, cyclosporin A dose-dependently increased IL-12Rbeta2 mRNA expression. These first data on IL-12Rbeta2 gene regulation indicate a TATA-less promoter, depending on SP-1/SP-3 transcription factors, and a negative regulatory NFAT element at -206. This element may contribute to the overall low level of IL-12Rbeta2 expression on Th cells.

Characterization of Phloem iron and its possible role in the regulation of fe-efficiency reactions.

;Fe-efficiency reactions' are induced in the roots of dicotyledonous plants as a response to Fe deficiency. The role of phloem Fe in the regulation of these reactions was investigated. Iron travels in the phloem of Ricinus communis L. as a complex with an estimated molecular weight of 2400, as determined by gel exclusion chromatography. The complex is predominantly in the ferric form, but because of the presence of reducing compounds in the phloem sap, there must be a fast turnover in situ between ferric and ferrous (k approximately 1 min(-1)). Iron concentrations in R. communis phloem were determined colorimetrically or after addition of (59)Fe to the nutrient solution. The iron content of the phloem in Fe-deficient plants was lower (7 micromolar) than in Fe-sufficient plants (20 micromolar). Administration of Fe-EDTA to leaves of Phaseolus vulgaris L. increased the iron content of the roots within 2 days, and decreased proton extrusion and ferric chelate reduction. The increase in iron content of the roots was about the same as the difference between iron contents of roots grown on two iron levels with a concomitantly different expression of Fe-efficiency reactions. We conclude that the iron content of the leaves is reflected by the iron content of the phloem sap, and that the capacity of the phloem to carry iron to the roots is sufficient to influence the development of Fe-efficiency reactions. This does not preclude other ways for the shoot to influence these reactions.

Involvement of superoxide radical in extracellular ferric reduction by iron-deficient bean roots.

The recent proposal of Tipton and Thowsen (Plant Physiol 79: 432-435) that iron-deficient plants reduce ferric chelates in cell walls by a system dependent on the leakage of malate from root cells was tested. Results are presented showing that this mechanism could not be responsible for the high rates of ferric reduction shown by roots of iron-deficient bean (Phaseolus vulgaris L. var Prélude) plants. The role of O(2) in the reduction of ferric chelates by roots of iron-deficient bean plants was also tested. The rate of Fe(III) reduction was the same in the presence and in the absence of O(2). However, in the presence of O(2) the reaction was partially inhibited by superoxide dismutase (SOD), which indicates a role for the superoxide radical, O(2) ([unk]), as a facultative intermediate electron carrier. The inhibition by SOD increased with substrate pH and with decrease in concentration of the ferrous scavenger bathophenanthroline-disulfonate. The results are consistent with a mechanism for transmembrane electron transport in which a flavin or quinone is the final electron carrier in the plasma membrane. The results are discussed in relation to the ecological importance that O(2) ([unk]) may have in the acquisition of ferric iron by dicotyledonous plants.