Reduction of serum Interleukin-1-like activity after treatment with dexamethasone

The ability of steroids to modulate the appearance of Interleukin-1(IL-1) in vivo was evaluated in a model of endotoxin shock. High levels of IL-1 were found in serum from A/J mice which were sensitized with P. acnes and challenged with bacterial lipopolysaccharide (LPS). The factor appeared in the serum 2-4 hours after LPS challenge and was dependent on the period of P. acnes sensitization and the dose of LPS. Treating the mice with dexamethasone prior to LPS challenge resulted in significantly lower thymocyte proliferative activity in the serum. Three experiments demonstrated that this reduced activity reflects a decrease in IL-1. 1) The reduced activity was not due to the presence of proliferation inhibitors since mixing the serum from dexamethasone-treated mice with purified IL-1 or adding the equivalent amount of steroid directly to thymocyte cultures did not reduce the degree of proliferation. 2) When the serum was fractionated by gel filtration, the proliferative activity for both control and steroid treated sera eluted at 10-16 kilodaltons; however, the activity was nearly 50% less in the sample from steroid-treated mice. 3) In addition to thymocyte proliferative activity, IL-1 induces an increase in the serum titer of the acute phase protein known as serum amyloid A. Both serum- and gel-purified samples were able to induce the SAA, but again the samples from steroid-treated mice were much less active. We conclude that the factor produced in vivo has the properties of IL-1 and that the serum titre of the factor is reduced by dexamethasone treatment.