PURIFIED SHIGA-LIKE TOXINS INDUCE EXPRESSION OF PROINFLAMMATORY CYTOKINES FROM MURINE PERITONEAL-MACROPHAGES

Infections with Shiga toxin-producing Shigella dysenteriae type 1 and Shiga-like toxin (SLT)-producing Escherichia coli cause outbreaks of b loody diarrhea in which patients are at risk for developing life-threa tening complications involving the renal and central nervous systems. Histopathology studies and in vitro experiments suggested that the tox ins damage toxin receptor-expressing endothelial cells (EC) lining glo merular and central nervous system capillaries. In the presence of ind ucible host factors (cytokines), EC sensitivity to SLT toxicity was in creased similar to 1 million-fold. We hypothesized that to manifest th e vascular lesions characteristic of infection with toxin-producing ba cteria, two signals were needed: systemic toxins and elevated proinfla mmatory cytokines (tumor necrosis factor alpha [TNF-alpha], interleuki n 1 [IL-1], and IL-6). Human EC do not secrete these cytokines when st imulated with SLTs in vitro, Suggesting that additional cells may be i nvolved in pathogenesis. Therefore, we carried out comparative analyse s of the capacity of purified (endotoxin-free) SLTs and lipopolysaccha rides (LPS) to induce cytokine mRNA and proteins from murine macrophag es, The cells were essentially refractory to SLT cytotoxicity, express ing low to undetectable levels of toxin receptor. SLTs and LPS induced TNF activity and IL-6 expression from macrophages, although dose resp onse and kinetics of cytokine induction differed. LPS was a more effec tive inducing agent than SLTs. SLT-I-induced TNF activity and IL-6 exp ression were delayed compared with induction mediated by LPS. IL-1 alp ha production required similar to 24 h of exposure to SLTs or LPS. Mac rophages from LPS-hyporesponsive C3H/HeJ mice produced low levels of T NF activity when treated with SLT-I, suggesting that LPS and SLTs may utilize separate signaling pathways for cytokine induction.