Interleukin-1 (IL-1) inhibits growth of cytomegalovirus in human marrow stromal cells: inhibition is reversed upon removal of IL-1.

A Toledo strain cytomegalovirus (CMV) containing the gene for green fluorescent protein (GFP) under the control of elongation factor-1 promoter was used to study infection of human marrow stromal cells. Two stromal cell lines were used: HS-5, which secretes copious amounts of known cytokines and interleukins; and HS-27a, which does not secrete these activities. CMV growth and spread was monitored by counting green plaques and quantitating GFP intensity. Initial studies indicated that, whereas HS-5 and 27a have similar susceptibilities to infection, as evidenced by the same number of GFP+ cells at day 2, HS-5 appears more resistant to growth and spread of CMV. Furthermore, conditioned media from HS-5 (HS-5 CM) inhibited CMV plaque formation in HS-27a, suggesting that factors secreted by HS-5 are responsible for limiting CMV growth. Neutralizing antibodies against interleukin-1alpha (IL-1alpha) and IL-1beta completely blocked the ability of HS-5 CM to limit viral growth, suggesting that IL-1, which is known to be present in HS-5 CM, is responsible for this effect. When exogenous IL-1beta was added to CMV-infected HS-27a, both the number of plaques and the intensity of GFP was significantly reduced in IL-1-treated HS-27a compared with untreated HS-27a (the number of plaques by day 18 was 20 +/- 3 v 151 +/- 12/well, respectively; GFP intensity was 535 +/- 165 v 6,516 +/- 652/well, respectively, in 4 separate experiments). At day 21, when IL-1beta-treated, CMV-infected cultures were passaged and then cultured in the absence of IL-1beta, CMV growth progressed with the kinetics of the original untreated culture, indicating that the IL-1beta effect is reversible. Because HS-27a expresses the type I IL-1 receptor, we speculate that the antiviral effects are mediated through IL-1-induced changes in cellular gene expression. DNA chip analysis of mRNA from IL-1beta-treated and nontreated HS-27a cells has identified some candidate molecules.