Osteoclasts and effects of interleukin 4 in development of chronic osteomyelitis.

The cellular response to trauma and infection was studied in a murine model of posttraumatic osteomyelitis. Osteoclast response differed markedly depending on whether infection with Staphylococcus aureus accompanied the bone trauma. In animals recovering from sterile trauma, osteoclastic activity that was limited to the damaged or dead bone fragments caused rapid elimination of all recognizable dead bone within 1 week. New bone was laid down in an orderly fashion. Animals with superimposed infection had an intense polymorphonuclear leukocyte response develop. Additionally, osteoclasts behaved as acute inflammatory responders with substantial activity at the margins of the infected site and at previously uninjured tibial cortex adjacent to the infection. Despite the exuberant osteoclast response, bony fragments were not resorbed (for at least 4 weeks after the trauma), that is, sequestra developed, and new bone was laid down over morphologically dead bone and on the cortex (involucrum). When the inhibitory cytokine, interleukin 4 was given in a single dose with the bacterial inoculum, the osteoclast response was moderated with almost complete elimination of osteoclast activity at normal tibial cortex adjacent to the infected site. The limitation of osteoclastic activity did not impair the host's containment of bacterial growth.

Effects of transforming growth factor-beta and IL-1 alpha on prostaglandin synthesis in serum-deprived osteoblastic cells.

We investigated the effects that the combination of IL-1 alpha and transforming growth factor-beta (TGF-beta) had on PGE2 production in a murine clonal osteoblastic cell line MC3T3-E1 and primary rat calvarial osteoblast-like cells. In serum-supplemented medium, IL-1 alpha was a potent stimulator of PGE2 production in MC3T3-E1 cells (50-fold increase with 0.1 ng/ml). TGF-beta (10 ng/ml) had only a small effect alone and no additional effect on IL-1 alpha-induced responses. In serum-deprived MC3T3-E1 cells, PGE2 responses to IL-1 alpha were either absent or markedly reduced. TGF-beta alone had small effects. However, simultaneous addition of TGF-beta with IL-1 alpha to MC3T3-E1 cells partially restored the ability of IL-1 alpha to generate a PGE2 response (10-fold increase in PGE2 with 0.1 ng/ml of both IL-1 alpha and TGF-beta). As with MC3T3-E1 cells, serum-deprived primary fetal rat calvarial osteoblastic cells also did not respond to IL-1 alpha, unless TGF-beta was present in the medium (sixfold increase in PGE2 with 0.1 ng/ml IL-1 alpha and 10 ng/ml TGF-beta). The synergistic effect of TGF-beta and IL-1 alpha was specific for PGE2 responses, because these factors did not synergistically affect cell proliferation, collagen and noncollagen protein synthesis, or alkaline phosphatase activity. The observed synergy was not associated with changes in the steady state cyclooxygenase (PGH synthase) mRNA levels. However, it did correlate with increased release of [3H]arachidonic acid from prelabeled serum-depleted MC3T3-E1 cells. Hence, the synergistic interactions of IL-1 alpha and TGF-beta on PGE2 appear to occur through an increase in the release of arachidonic acid substrate from phospholipid pools. These effects may be important for both normal bone turnover and the responses of bone to inflammatory and immune stimuli.