TC6 counteracts transferrin’s immunosuppressive functions to block transferrin’s inhibition on LPS-induced inflammatory responses both in vitro and in vivo (Figs. S10G and H, S13, and S19) and to inhibit the protective effects of transferrin on intestinal immune imbalance induced by gut microbial dysbiosis, and consequently diminishes transferrin’s improvement on pathological insults in the colitis models (Fig. S7I and J and Fig. S24), demonstrating that transferrin’s immunosuppressive phenotypes seen in the cell and animal models are mediated by transferrin–CD14 interaction. Here, CD14 is linked to colitis.