LPS-induced sTNF-receptor release in vivo in a murine model. Investigation of the role of tumor necrosis factor, IL-1, leukemia inhibiting factor, and IFN-gamma.

TNF, a primary mediator of the response to infection, can be injurious to the organism when present in excessive quantities. Circulating soluble TNF receptors (sTNFR) appear to represent a natural mechanism that protects against circulating TNF. Two soluble TNF receptors (sTNFR-P55 and sTNFR-P75) circulate in vivo and are up-regulated in response to endotoxin. In this study, we investigated the kinetics of LPS-induced sTNFR release and the role of the cytokines TNF, leukemia inhibiting factor, IFN-gamma, and IL-1 in this process. The results show that LPS injection results in a rapid increase in levels of both sTNFR. Although sTNFR-P55 decreases after a peak at 30 min, sTNFR-P75 levels show a peak after 4 to 8 h, after which they slowly diminish. Both human TNF and murine TNF are capable of increasing levels of both sTNFR. Blocking circulating TNF by administration of 3 different anti-TNF agents before LPS injection (mAb to murine TNF, sTNFR55-Fc or sTNFR75-Fc) results in a significant increase of sTNFR-P55 levels, whereas only both sTNFR-Fc constructs also significantly increase sTNFR-P75 levels. Although IL-1 receptor antagonist pretreatment before LPS has no effect on TNF or sTNFR levels, leukemia inhibiting factor pretreatment significantly increases sTNFR-P55 levels. Pretreatment with anti IFN-gamma mAb before LPS results in a significant reduction in TNF and sTNFR-P55 levels, but sTNFR-P75 levels are significantly increased. Our data show that both sTNFR can be up-regulated by LPS and TNF. The influence of TNF, leukemia inhibiting factor, IL-1, and IFN-gamma on the kinetics of LPS-induced circulating sTNFR is discussed in the context of the pathophysiology of LPS-induced disease.