Collagen dose-response at 56 days after exposure to MWCNTs. As shown in Figure 7, there was a progressive increase in the average thickness of the alveolar connective tissue thickness versus aspiration dose of MWCNTs. At a dose of 80 ug the average thickness was increase by 73% over control. Data are means ± SE for an N of 8 animals per group. * indicates statistical significance P < 0.05 vs. DM -treated control mice.