INTERLEUKIN-6 EXPRESSION AND HISTOMORPHOMETRY OF BONES FROM MICE DEFICIENT IN RECEPTORS FOR INTERLEUKIN-1 OR TUMOR-NECROSIS-FACTOR

We examined the roles of interleukin-1 Type I I receptor (IL-1R1) and tumor necrosis factor receptor 1 (TNFR1) in bone metabolism using mice rendered deficient in these receptors by gene targeting, Sections of decalcified paraffin-embedded calvariae and humeri from 11- to 12-week -old mice deficient in IL-1 Type I receptor (IL-1R1-/-) or TNF recepto r 1 (TNFR1-/-) were examined by histomorphometry. Wild-type mice (C57B L/6J x 129/J, WILD) served as controls, Interleukin-6 (IL-6) productio n in primary osteoblastic and bone marrow stromal cell cultures in res ponse to parathyroid hormone (PTH, 100 ng/ml), IL-alpha (10 ng/ml), an d TNF-alpha (10 ng/ml) was also examined, IL-1R1-/- and TNFR1-/- mice were viable and appeared phenotypically normal, However, the body weig hts of the IL-1R1-/- mice were 30% less than WILD, while the TNFR1-/- mice weighed 30% more than WILD mice of equivalent age. Calvariae and humeri of IL-1R1-/- and TNFR1-/- mice were normal with respect to trab ecular bone volume, osteoclast number, osteoclast surface, growth plat e widths, and cortical thickness. Receptor deficiency was confirmed by determining the ability of PTH, IL-1 alpha; and TNF-alpha to stimulat e IL-6 in the media of primary calvaria-derived osteoblastic cell cult ures from CD-I and cytokine receptor-deficient mice. After 23 h of tre atment, IL-1 alpha and TNF-alpha did not stimulate IL-6 production in osteoblasts from IL-1R1-/- and TNFR1-/- mice, respectively. In contras t, PTH increased IL-6 levels in the cells from all mice, IL-6 protein levels in bone marrow supernatants and conditioned media from untreate d bone marrow stromal cells were undetectable in WILD. IG-1R1-/-, and TNFR1-/- mice. PTH, IL-1 alpha: and TNF-alpha increased IL-6 mRNA and protein production in the WILD bone marrow stromal cells, In contrast, PTH and TNF-alpha increased IL-6 mRNA and protein levels in IL-1R1-/- bone marrow stromal cells while IL-1 alpha had no effect, These findi ngs demonstrate that normal bone development in mice can occur in the absence of IL-1R1 or TNFR1 expression.