Conventional dendritic cells regulate the outcome of colonic inflammation independently of T cells

Abstract

We explored the physiological role of conventional dendritic cells (cDCs) in acute colitis induced by a single cycle of dextran sodium sulfate administration. Depending on their mode of activation and independently of T cells, cDCs can enhance or attenuate the severity of dextran sodium sulfate-induced colitis. The latter beneficial effect was achieved, in part, by IFN-1 induced by Toll-like receptor 9-activated cDCs. IFN-1 inhibits colonic inflammation by regulating neutrophil and monocyte trafficking to the inflamed colon and restraining the inflammatory products of tissue macrophages. These data highlight a novel role of cDCs in the regulation of other innate immune cells and position them as major players in acute colonic inflammation.

Fig. 1.

Depletion of cDCs suppresses DSS-induced colitis. tg-DTR mice were given DSS for 7 days, injected with DT or PBS i.p. on days 5 and 6, and analyzed on day 7 as described in Materials and. Methods. (A) DAI. (B) HS. (C) All mice were weighed daily, and data are presented as mean body weight ± SD. *, P < 0.05. (D) Histological evaluation of colon. Paraffin sections of colons from tg-DTR mice (n = 7 mice per group), treated as indicated, were prepared and stained with H&E. Ulcerated areas are indicated by arrows. (Scale bar: 10 μm.) (E) Photomicrographs of representative areas from DSS- and DSS/DT-treated mice as indicated. Arrows highlight PMN infiltrates. (Scale bar: 5 μm.) (F) PMNs per HPF were counted in the proximal and distal colons of DSS- and DSS/DT-treated tg-DTR mice (n = 7 mice per group). P values were calculated by Mann–Whitney test. (G) Freshly isolated colon explants were cultured for 24 h in complete RPMI medium 1640, and cytokine release was measured by ELISA. Results represent mean cytokine levels (± SD; pg/mg colonic tissue) in samples. Data are representative of two independent experiments.

Fig. 2.

Depletion of cDCs in TLR9 ligand-treated mice aggravates DSS-induced colitis. tg-DTR mice were injected with PBS or ISS-ODN (10 μg per mouse) s.c. 2 h before DSS administration. On days 5 and 6, mice were injected with DT or PBS and analyzed on day 7 as described in Materials and Methods. (A) DAI. (B) HS. (C) All mice were weighed daily, and data are presented as mean body weight ± SD. *, P < 0.05. (D) Histological evaluation of colon. Paraffin sections of the colon from tg-DTR mice (n = 7 mice per group), treated as indicated, were prepared and stained with H&E. Ulcerated areas are indicated by arrows. P values were calculated by Mann–Whitney test. (Scale bar: 10 μm.) (E) Photomicrographs of representative areas from ISS/DSS- and ISS/DSS/DT-treated mice as indicated. Arrows highlight PMN infiltrates. (Scale bar: 5 μm.) (F) PMNs per HPF were counted in the proximal colon and distal colon of ISS/DSS- and ISS/DSS/DT-treated tgDTR mice (n = 7 mice per group). P values were calculated by Mann–Whitney test. (G) Freshly isolated colon explants from mice were cultured 24 h in complete RPMI medium 1640, and cytokine release was measured by using ELISA. Results represent mean cytokine levels (± SD; pg/mg colonic tissue) in samples. Data are representative of two independent experiments.

Fig. 3.

Administration of rIFN-β or adoptive transfer of cDCs reverses the outcome of colitis. ISS/DSS-treated tg-DTR mice were injected i.p. with mouse rIFN-β (1,000 units per mouse per day), mouse IL-10 (1 μg per mouse per day), or PBS on days 5 and 6 of DT administration. (A) Change in body weight (data presented as mean body weight ± SD; *, P < 0.05) and DAI. (B) SP-cDCs were isolated on day 5 from ISS/DSS-treated B6 mice as described in Materials and Methods and were adoptively transferred i.p. into ISS/DSS-treated tg-DTR mice (2 × 10⁵ cells per mouse) on the fifth day of DSS administration. DT was injected on days 5 and 6. Colitis was evaluated on day 7 of DSS administration. (C) SP-cDCs were isolated on day 5 from DSS-treated B6 mice and were adoptively transferred i.p. into DSS-treated tg-DTR mice (2 × 10⁵ cells per mouse) on the fifth day of DSS administration. DT was injected on days 5 and 6. Colitis was evaluated on day 7 after DSS administration. P values were calculated by Mann–Whitney test and were representative of two independent experiments (n = 4–6 mice per group).

Fig. 4.

IFN-1 accelerates the resolution of colonic inflammation. (A) B6 (WT) and IFN-α/βR^−/− mice were given DSS for 7 days and analyzed on days 7 and 14 as described in Materials and Methods. All mice were weighed on days 0, 3, 7, 10, and 14. Data are presented as mean body weight ± SD, n = 4 mice per group. (B) PMN and Mac (F4/80+) count per HPF in the distal colon on days 7 and 14 after DSS treatment in WT(B6) or IFN-α/βR^−/− (B6) mice. P values were calculated by Mann–Whitney test. (C) Freshly isolated colon explants from mice were cultured 24 h in complete RPMI medium 1640, and cytokine release in the supernatants was measured by Luminex. Results represent mean chemokine levels (± SD; pg/mg or ng/mg colonic tissue) in samples. Data are representative of two independent experiments.