Trypanosomes lacking trypanothione reductase are avirulent and show increased sensitivity to oxidative stress

In Kinetoplastida, trypanothione and trypanothione reductase (TRYR) provide an intracellular reducing environment, substituting for the glutathione-gl utathione reductase system found in most other organisms. To investigate th e physiological role of TRYR in Trypanosoma brucei, we generated cells cont aining just one trypanothione reductase gene, TRYR, which was under the con trol of a tetracycline-inducible promoter. This enabled us to regulate TRYR activity in the cells from less than 1% to 400% of wild-type levels by adj usting the concentration of added tetracycline. In normal growth medium (wh ich contains reducing agents), trypanosomes containing less than 10% of wil d-type enzyme activity were unable to grow, although the levels of reduced trypanothione and total thiols remained constant. In media lacking reducing agents, hypersensitivity towards hydrogen peroxide (EC50 = 3.5 mu M) was o bserved compared with the wild type (EC50 = 223 mu M). The depletion of TRY R had no effect on susceptibility to melarsen oxide. The infectivity and vi rulence of the parasites in mice was dependent upon tetracycline-regulated TRYR activity: if the trypanosomes were injected into mice in the absence o f tetracycline, no infection was detectable; and when tetracycline was with drawn from previously infected animals, the parasitaemia was suppressed.