Summary Endodontic infections are polymicrobial infections resulting in bone destruction and tooth loss. The host response to these infections is complex, including both innate and adaptive mechanisms. Osteopontin (OPN), a secreted, integrin‐binding protein, functions in the regulation of immune responses and enhancement of leucocyte migration. We have assessed the role of OPN in the host response to endodontic infection using a well‐characterized mouse model. Periapical bone loss associated with endodontic infection was significantly more severe in OPN‐deficient mice compared with wild‐type 3 weeks after infection, and was associated with increased areas of inflammation. Expression of cytokines associated with bone loss, interleukin‐1α (IL‐1α) and RANKL, was increased 3 days after infection. There was little effect of OPN deficiency on the adaptive immune response to these infections, as there was no effect of genotype on the ratio of bacteria‐specific immunoglobulin G1 and G2a in the serum of infected mice. Furthermore, there was no difference in the expression of cytokines associated with T helper type 1/type2 balance: IL‐12, IL‐10 and interferon‐γ. In infected tissues, neutrophil infiltration into the lesion area was slightly increased in OPN‐deficient animals 3 days after infection: this was confirmed by a significant increase in expression of neutrophil elastase in OPN‐deficient samples at this time‐point. We conclude that OPN has a protective effect on polymicrobial infection, at least partially because of alterations in phagocyte recruitment and/or persistence at the sites of infection, and that this molecule has a potential therapeutic role in polymicrobial infections.

The 1029 series of mammary epithelial cell lines (D6, GP+E, r3 and r3T) are progressively more transformed: the latter two by val 12 ras. These cell lines respond to TGFβ by undergoing early events of epithelial-mesenchymal transition (EMT), including morphological changes and redistribution of E-cadherin. Tumors formed by r3T cells in the choroid of the eye express vimentin, a late marker of EMT, possibly in response to TGFβ. In vitro, vimentin expression is induced in all the cell lines by TGFβ treatment, while cytokeratin expression is only slightly affected. Surprisingly, ras transformation results in a 10-fold suppression of vimentin expression. Neither suppression of vimentin by ras transformation nor induction by TGFβ are mediated by the vimentin promoter in r3T cells. In transient transfection assays, several human vimentin promoter constructs are more active in the low-expressing r3T cell line than in the vimentin-expressing mesenchymal cell line NIH3T3. In the r3T cells, there is no effect of TGFβ treatment for 9 days on the activity of either promoter. Azacytidine treatment does not affect vimentin expression in either NIH3T3 or r3T, suggesting that promoter methylation is not the mechanism of suppression by ras. Finally, the half life of the vimentin mRNA is similar in both the r3T cells and NIH3T3 cells. We conclude that the suppression of vimentin expression by ras, and the relief of this suppression by TGFβ, occurs in a promoter-independent fashion, possibly through sequences in the first or second intron.