With exposure to ox-LDL, MΦ and mAo cell interaction restores LPS- and LPS/IFNγ-induced IL-6 secretion which is contributed by the mAo cells. Secreted IL-6 measured in culture supernatants of MΦ cells (A) and TLR4-MΦ cells (B) alone and in co-culture with mAo cells after being treated with or without ox-LDL (50 μg/mL) for 24 hours and then activated with LPS (100 ng/mL) or with LPS (100 ng/mL) + IFNγ (250 ng/mL) is shown. MΦ cells after being exposed to ox-LDL (50 μg/mL) for 24 hours were also cultured in transwells with mAo cells present in the well as depicted in (C). Both MΦ cells in the transwell and mAo cells in the well were activated with LPS or LPS + IFNγ, and supernatants from the transwell and well compartments were assayed for IL-6 content separately (C). Ox-LDL-treated mAo and MΦ cells were exposed to CM (collected after ox-LDL exposure and LPS and LPS + IFNγ (L/I) activation) from the opposing cell type. IL-6 levels in the CM were subtracted from the supernatant values, and the net production is presented in (D). Data are presented as mean ± standard error of the mean and are representative of three experiments each with n = 4. *Significantly different from MΦ or TLR4-MΦ cells alone under same conditions; #significantly different from non-ox-LDL-treated counterpart; †significantly different from well and transwell supernatant; ‡significantly different from cultures exposed to CM. CM, conditioned medium; IFNγ, interferon-gamma; IL-6, interleukin-6; LPS, lipopolysaccharide; MΦ, bone marrow-derived macrophage; mAo, mouse aorta-derived mesenchymal progenitor; MSC, mesenchymal stem cell; ox-LDL, oxidized low-density lipoprotein; TLR4-MΦ, Toll-like receptor-4-deficient macrophage.