Escherichia coli Shiga toxin 1 (Stx1) blocks the activation of bovine peripheral (PBMC) and ileal intraepithelial lymphocytes (iIEL). The objectives of the study were to assess the impact of Stx1 on the expression of selected chemokine and cytokine genes in bovine lymphocytes (iIEL and PBMC) in vitro by real-time RT-PCR and by quantitation of intracellular cytokine proteins by flow cytometry.Freshly isolated iIEL were shown to harbour transcripts of chemokines and of TH1, TH2, and TH3 cytokines. While Stx1 did not alter the amount of mRNA specific for IL-2, IL-10, IFN-gamma, TGF-beta, IL-8, IP-10, and MCP-1 in cultured iIEL, minute concentrations of Stx1 led to an up to 40-fold increase of il-4 transcripts within 6-8 hrs of incubation. In addition, the effect of Stx1 on il-4 transcripts was specified to require the enzymatic activity of the holotoxin, as the StxB1 subunit alone did not affect iIEL. Nevertheless, in the presence of Stx1, iIEL retained their ability to synthesize proteins: 40 % of iIEL could be mitogen-stimulated to synthesize IFN-gamma while less than 10 % of the cells expressed IL-4 or TGF-beta proteins. The enhancement of il-4 transcripts in iIEL was not accompanied by apoptosis. Although Stx1 significantly impaired the iIEL blast transformation induced by mitogens in vitro and induced a marked redistribution of the Stx- receptor from the cell surface to intracellular compartments, Stx1-treated iIEL neither showed an increased exposure of phosphatidylserine on the cell surface nor an altered mitochondrial membrane potential. Comparative experiments with PBMC revealed that the effect on il-4 transcripts was specific for iIEL. Moreover, Stx1 hindered the translation of IFN-gamma in PBMC within 21 hrs.
Mucosal immune cells in cattle were found to be considerably sensitive to a cytokine-stimulating effect of Stx1. The results led to assume that the distinct induction of il-4 transcripts contributes to the establishment of a commensal-like colonization of the bovine intestinal mucosa by STEC.
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