The mechanisms by which bacteria resist cell-mediated immune responses to cause chronic infections are largely unknown. We report the identification of a large gene present in enteropathogenic strains of Escherichia coli (EPEC) that encodes a toxin that specifically inhibits lymphocyte proliferation and interleukin-2 (IL-2), IL-4, and gamma interferon production in response to a variety of stimuli. Lymphostatin, the product of this gene, is predicted to be 366 kDa and shares significant homology with the catalytic domains of the large clostridial cytotoxins. A mutant EPEC strain that has a disruption in this gene lacks the ability to inhibit lymphokine production and lymphocyte proliferation. Enterohemorrhagic E. coli strains of serotype O157:H7 possess a similar gene located on a large plasmid. Loss of the plasmid is associated with loss of the ability to inhibit IL-2 expression while transfer of the plasmid to a nonpathogenic strain of E. coli is associated with gain of this activity. Among 89 strains of E. coli and related bacteria tested, lifA sequences were detected exclusively in strains capable of attaching and effacing activity. Lymphostatin represents a new class of large bacterial toxins that blocks lymphocyte activation.Bacteria have evolved a number of mechanisms, including antiphagocytic factors, leukotoxins, and systems for iron chelation, to resist the nonspecific (innate) immune response of vertebrate hosts (25). In addition, several mechanisms to circumvent humoral immunity have been described, such as immunoglobulin A proteases and immunoglobulin-binding proteins. However, few bacterial factors that specifically interfere with cellular immune responses have been described (69). In addition, the mechanisms that allow certain bacterial pathogens to colonize hosts for prolonged periods remain obscure.Enteropathogenic Escherichia coli (EPEC) is a leading cause of diarrhea among infants in developing countries. EPEC is one of the few known bacterial causes of chronic diarrhea (24,34,55). EPEC strains are characterized by their ability to induce profound cytoskeletal rearrangements in host cells that result in the formation of adhesion pedestals upon which the bacteria rest (47). This phenomenon is known as the attaching and effacing effect. Enterohemorrhagic E. coli (EHEC) strains, a subgroup of Shiga-toxin-producing E. coli, also have attaching and effacing activity (26, 64). We previously reported that EPEC produce and secrete a high-molecular-weight, proteasesensitive factor that selectively inhibits production of interleukin-2 (IL-2), IL-4, IL-5, and gamma interferon by human peripheral and lamina propria mononuclear cells and inhibits proliferation of these cells (35,36,41). This inhibitory effect was observed regardless of whether the cells were stimulated by phorbol esters, mitogens, CD3 cross-linking, or antigen. The effect was also seen in macrophage-depleted T-cell populations and in Jurkat cells, indicating that this activity did not require participation of cells other than lymphocytes. ...

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Prohibitin (PHB) is an evolutionarily conserved and ubiquitously expressed protein whose expression or function in intestinal diseases is not known. In this study, we examined the expression and role of PHB in oxidative stress associated with inflammatory bowel disease. Our results show that PHB primarily localizes to the mitochondria in intestinal epithelial cells. Its expression is down-regulated during active human Crohn's disease, experimental colitis in vivo, and oxidative stress in vitro. PHB overexpression increases the expression of glutathione-S-transferase pi and protects from oxidant-induced depletion of glutathione. Finally, PHB overexpression decreases accumulation of reactive oxygen metabolites, as well as increased permeability induced by oxidative stress in intestinal epithelial cells. Together, these results suggest that PHB constitutes a previously unrecognized cellular defense against oxidant injury. Thus, strategies to modulate PHB levels may constitute a novel therapeutic approach for intestinal inflammatory diseases, wherein oxidative stress plays a critical role in tissue injury and inflammation.

Recombinant human interleukin 6 (rhIL 6) was injected i.p. into male Wistar rats to investigate its role as a mediator of the acute-phase response. Hepatic mRNA levels of beta-fibrinogen, alpha 2-macroglobulin, cysteine proteinase inhibitor, alpha 1-acid glycoprotein and albumin were measured at different times after the administration of rhIL 6. Maximal increases of mRNA concentrations were observed already 4 h after the injection of rhIL 6 leading to 4.8-, 19.7-, 10- and 16-fold stimulations in mRNA levels of beta-fibrinogen, alpha 2-macroglobulin, cysteine proteinase inhibitor or alpha 1-acid glycoprotein, respectively. The rhIL 6-induced stimulation of acute-phase protein mRNA was much more rapid than the acute-phase induction after turpentine, where maximal mRNA levels were found between 16 and 24 h. For all acute-phase proteins studied, the stimulation of mRNA synthesis was found to be dependent on the dose of rhIL 6 injected. In the case of alpha 2-macroglobulin mRNA a sex-specific induction by rhIL 6 was found. Only male rats showed an acute-phase response, whereas in female rats an acute-phase reaction of alpha 2-macroglobulin mRNA was not inducible by IL 6. The increases in mRNA levels of the acute-phase proteins studied were followed by corresponding changes of the proteins in the serum determined by rocket immunoelectrophoresis. It is concluded that IL 6 represents a potent mediator of the acute-phase response in the rat.