Cloning and Expression of theActinobacillus actinomycetemcomitansThioredoxin (trx) Gene and Assessment of Cytokine Inhibitory Activity

Abstract

Thioredoxin is a ubiquitous redox control and cell stress protein. Unexpectedly, in recent years, thioredoxins have been found to exhibit both cytokine and chemokine activities, and there is increasing evidence that this class of protein plays a role in the pathogenesis of inflammatory diseases. In spite of this evidence, it has been reported that the oral bacterium and periodontopathogenActinobacillus actinomycetemcomitanssecretes an immunosuppressive factor (termed suppressive factor 1 [SF1] [T. Kurita-Ochiai and K. Ochiai, Infect. Immun. 64:50–54, 1996]) whose N-terminal sequence, we have determined, identifies it as thioredoxin. We have cloned and expressed the gene encoding the thioredoxin ofA. actinomycetemcomitansand have purified the protein to homogeneity. TheA. actinomycetemcomitans trxgene has 52 and 76% identities, respectively, to thetrxgenes ofEscherichia coliandHaemophilus influenzae. Enzymatic analysis revealed that the recombinant protein had the expected redox activity. When the recombinant thioredoxin was tested for its capacity to inhibit the production of cytokines by human peripheral blood mononuclear cells, it showed no significant inhibitory capacity. We therefore conclude that the thioredoxin ofA. actinomycetemcomitansdoes not act as an immunosuppressive factor, at least with human leukocytes in cultures, and that the identity of SF1 remains to be elucidated.