Early osteoclast precursors, in the form of murine bone marrow macrophages (BMMs), while expressing no detectable αvβ3 integrin, contain abundant αvβ5 and attach to matrix in an αv integrin-dependent manner. Furthermore, αvβ5 expression by osteoclast precursors progressively falls as they assume the resorptive phenotype. We find the osteoclastogenic agent, tumor necrosis factor-α, (TNF) down-regulates αvβ5 expression by BMMS via attenuation of β5 messenger RNA (mRNA) t1/2. Using BMMs from TNF receptor knockout mice we establish the p55 receptor transmits the β5 suppressive effect. The functional implications of TNF-mediated αvβ5 down-regulation are underscored by the capacity of an αv inhibitory peptide mimetic to prevent spreading by BMMs expressing abundant αvβ5 while failing to impact those in which the integrin has been diminished by TNF. Finally, β5 mRNA in BMMs of wild-type mice administered lipopolysaccharide (LPS) progressively falls with time of in vivo treatment. Alternatively, β5 mRNA does not decline in BMMs of LPS-treated mice lacking both TNF receptors, documenting down-regulation of the β5 integrin subunit, in vivo, is mediated by TNF. Thus, matrix attachment of osteoclast precursors and mature osteoclasts are governed by distinct αv integrins which are differentially regulated by specific cytokines.