The microstructure of secondary lymphoid organs that support immune cell trafficking.

Immune cell trafficking in the secondary lymphoid organs is crucial for an effective immune response. Recirculating T cells constantly patrol not only secondary lymphoid organs but also the whole peripheral organs. Thoracic duct lymphocytes represent an ideal cell source for analyzing T cell trafficking: high endothelial venules (HEVs) allow recirculating lymphocytes to transmigrate from the blood directly, and recirculating T cells form a cluster with dendritic cells (DCs) to survey antigen invasions even in a steady state. This cluster becomes an actual site for the antigen presentation when DCs have captured antigens. On activation, effector and memory T cells differentiate into several subsets that have different trafficking molecules and patterns. DCs also migrate actively in a manner depending upon their maturational stages. Danger signals induce the recruitment of several DC precursor subsets with different trafficking patterns and functions. In this review, we describe general and specialized structures of the secondary lymphoid organs for the trafficking of T cells and DCs by a multicolor immunoenzyme staining technique. The lymph nodes, spleen, and Peyer's patches of rats were selected as the major representatives. In vivo trafficking of subsets of T cells and DCs within these organs under steady or emergency states are shown and discussed, and unsolved questions and future prospects are also considered.

Systemic transmigration of allosensitizing donor dendritic cells to host secondary lymphoid organs after rat liver transplantation.

UNLABELLED: Donor dendritic cell (DC) migration and allosensitization in host secondary lymphoid organs after liver transplantation are ill defined. We used rat models to investigate graft-derived cells and intrahost allosensitization. Liver transplantation induced diffuse blood-borne migration of donor major histocompatibility class II antigen-positive (MHCII(+)) cells and MHCI(+) cells from the graft to host secondary lymphoid organs, not only the spleen, but also lymph nodes and Peyer's patches. The migrated MHCII(+) cells included DCs and some T cells and B cells. The DCs formed clusters with host BrdU(+) cells where they up-regulated CD86(+), and a CD8(+) T cell proliferative response originated within 24 hours after liver transplantation, demonstrating that these DCs can quickly mature and trigger direct allosensitization in host lymphoid organs. Transfer of allogeneic bone marrow cells also induced DC transmigration and a similar host response. In contrast, allogeneic thoracic duct lymph cells contained many fewer transmigrating DCs, and their transfer induced a comparable T cell response but significantly weaker CD8(+) T cell proliferation. Thus, there is a different outcome via the indirect pathway by host DCs that have captured donor alloantigens. CONCLUSION: The rat liver as well as bone marrow contains an immature DC population that can systemically transmigrate through blood vessel walls of the host secondary lymphoid organs, quickly mature, and induce diffuse intrahost CD8(+) T cell responses, which may promote graft rejection.

Predominant donor CD103+CD8+ T cell infiltration into the gut epithelium during acute GvHD: a role of gut lymph nodes.

The existence of donor effector cell subsets responsible for either gut or skin graft-versus-host disease (GvHD) is still undetermined. We examined the trafficking and role of donor CD8(+) intra-epithelial lymphocytes (IELs) in the gut and skin epithelia concerning alpha E beta 7 integrin (CD103) expression, using a rat acute lethal GvHD model. Most CD103(+) donor cells were CD8(+) and showed a proliferative activity in the target epithelia. On the other hand, activated donor T cells in the host lymphoid tissues did not express CD103, indicating the presence of CD8(+) IEL precursors in the lymphoid tissues that may up-regulate CD103 only after migrating to the target organs. At the late stage of GvHD, while >80% of the donor CD8(+) IELs were CD103(+) in the gut epithelium, both CD4(+) and CD103(+)CD8(+) T cells evenly accumulated in the skin epidermis. The CD103 expression by donor CD8(+) IELs especially in the gut was also correlated with the clinical GvHD manifestations. Furthermore, the selective removal of gut lymph nodes (LNs) but not skin LNs suppressed the infiltration of CD103(+) donor IELs in the gut and alleviated intestinal GvHD. In conclusion, CD103(+)CD8(+) donor T cells predominantly infiltrate into the gut epithelium and are responsible for the manifestations of intestinal GvHD. This pathology is at least partly dependent on the gut LNs.

Trafficking of recirculating lymphocytes in the rat liver: rapid transmigration into the portal area and then to the hepatic lymph.

BACKGROUND: We have investigated how recirculating lymphocytes patrol the liver in a normal steady state. METHODS: Thoracic duct lymphocytes of congeneic rats were intravenously transferred to host rats and donor cell trafficking in the liver and hepatic lymph was examined. Host hepatic lymph nodes (HLNs) were selectively removed, which allowed liver-derived donor cells to collect in the thoracic duct without transit in the intervening HLNs. RESULTS: The number of donor cells in the thoracic duct lymph significantly increased over the baseline 3, 5 and 11 h after transfer in the HLN-removed, non-pretreated, and HLN-ligated (in which a lymph efflux was blocked) groups, respectively. Histologically, donor cells appeared in the portal area from 0.5 h after transfer and frequently attached to the basal lamina of portal vein both externally and internally. Three hours after transfer, a few donor cells appeared in the subcapsular sinus of HLNs. CONCLUSION: The minimal transit time of rat recirculating lymphocytes is 3-4 h in the liver and 5-8 h in the hepatic LNs, in a normal steady state. Recirculating lymphocytes might transmigrate through the portal vein as well as the sinusoid in the periportal zone. This rapid transit might enable an efficient surveillance of the liver portal area by the recirculating lymphocytes.