A novel migration pathway for rat dendritic cells from the blood: hepatic sinusoids-lymph translocation

Abstract

The migration pathways for dendritic cells (DC) from the blood are not yet completely resolved. In our previous study, a selective recruitment of DC progenitors from the blood to the liver was suggested. To clarify the role of the hepatic sinusoids in the migration of blood DC, relatively immature DC and mature DC were isolated from hepatic and intestinal lymph, and intravenously transferred to allogeneic hosts. It was then possible to detect small numbers of DC within secondary lymphoid tissues either by immunostaining for donor type major histocompatibility complex class I antigen or, at much higher sensitivity, for bromodeoxyuridine incorporated by proliferating cells (mainly T lymphocytes), which responded to the alloantigen presented by the administered DC. The intravenously injected DC accumulated in the paracortex of regional lymph nodes of the liver via a lymph-borne pathway. Intravenously injected fluorochrome-labeled syngeneic DC behaved similarly. In contrast, very few DC were found in spleen sections and were hardly detectable in other lymph nodes or in other tissues. An in situ cell binding assay revealed a significant and selective binding of DC to Kupffer cells in liver cryosections. It is concluded that rat DC can undergo a blood-lymph translocation via the hepatic sinusoids, but not via the high endothelial venules of lymph nodes. Hence the hepatic sinusoids may act as a biological concentrator of blood DC into the regional hepatic nodes. Kupffer cells may play an important role in this mechanism.

Figure 3

Proliferative response in host tissues 3 d after 10⁶ cell transfer. After transferring allogeneic latex-laden DC, the celiac and parathymic LNs showed a significant increase in the number of BrdU⁺ cells (*P = 0.03) compared with that after transfer of unseparated cells and syngeneic latex-laden DC. In posterior mediastinal LNs, there was no significant difference in proliferation between allogeneic and syngeneic latex-laden DC. No significant proliferative response was observed in cervical or mesenteric LNs, or (data not shown) Peyer's patches, liver, and thymus. Data are expressed as mean ± SD. Bars represent SD. Three rats per group were examined.

Figure 4

Proliferative response in host spleen 3 d after 10⁶ cell transfer. Allogeneic latex-laden DC and unseparated cells induced host cell proliferation, but there was no significant difference between them (P >0.05). Data are expressed as mean ± SD. Bars represent SD. Three rats per group were examined.

Figure 6

The dose responsiveness of the proliferative response in celiac LNs 3 d after cell transfer. Allogeneic latex-laden DC induced a significant increase at a dose of 10⁵ (P = 0.03 when compared with unseparated cells) and the maximum response at a dose of 3 × 10⁵ and 10⁶ cells. In contrast, 100 times more allogeneic unseparated cells were required to induce a comparable proliferative response. Data are expressed as mean ± SD. Bars represent SD. Three to six rats per group were examined.

Figure 7

The time kinetics of the proliferative response in celiac LNs after transfer of 3 × 10⁵ allogeneic DC. A slight increase of BrdU⁺ cells at 1 d, but significant proliferation 2–3 d, after cell transfer were observed. Data are expressed as mean ± SD. Bars represent SD. Three to six rats per group were examined.

Figure 9

In situ cell binding assay examined under differential interference light microscopy. DC showed preferential binding to either allogeneic (a) or syngeneic (not shown) liver cryosections compared to other tissues. In spleen (c), DC attached mainly to the marginal zone (Z) but not to the white pulp (W). In LN (d), bound DC were not obviously localized to specific areas. The same concentration of unseparated cells showed less binding to the liver cryosections than DC (b). P, portal area; M, medulla; C, cortex. ×160.