The appearance of fluorescein-labelled lymphocytes in lymph following in vitro or in vivo labelling: the route of lymphocyte recirculation through mesenteric lymph nodes.

Fluorescein isothiocyanate (FITC) has been used to study lymphocyte migration in sheep. After being labelled in vitro with FITC, lymphocytes migrated from blood into lymph at the same rate and with the same recovery as lymphocytes labelled with with the radioisotope 51chromium. The in vivo labelling of mesenteric lymph nodes (MLN) with FITC resulted in high numbers of labelled lymphocytes appearing in prescapular lymph. However, the appearance of the FITC-labelled lymphocytes in the prescapular lymph could be prevented by cannulating the main intestinal lymph duct prior to the in vivo labelling procedure. It was concluded that lymphocytes labelled in vivo within the MLN required an intact lymphatic system to reach the blood circulation and did not enter the venous circulation directly from the MLN.

Distribution of radiolabelled lymph cells in lymph nodes and the migratory properties of blood lymphocytes in sheep.

The results found in this study supported the concept of lymphocyte populations with preferential migratory pathways. Preferential localization of lymphocytes in lymph nodes could not explain the non-random lymphocyte migration patterns observed in sheep. The migration of lymphocytes isolated from the blood was similar to that of lymphocytes in the efferent lymph of a subcutaneous lymph node, but was different from the migration of lymphocytes isolated from efferent intestinal lymph. The subcutaneous lymph node did not need to be selective for lymphocytes which entered from blood. However, there must be a selective entry of a population of lymphocytes with preference for migrating through mesenteric lymph nodes into efferent intestinal lymph in order to observe the differential lymphocyte migration patterns exhibited by the lymphocytes in the efferent intestinal lymph of sheep.

The production of plasminogen activator by afferent but not efferent lymph cells emigrating from chronic granulomatous lesions in sheep.

Subcutaneous granulomas were induced in sheep by injecting Freund's adjuvant. At varying times thereafter afferent and efferent lymphatics draining the granulomas were cannulated. Lymph was collected for periods up to several days or weeks from either normal skin or from inflammatory lesions 15 to 120 days after the initiation of the lesions. The fibrinolytic activity of cells and cell culture medium in which cells were grown was assayed by using 125I-fibrin plates. No detectable enzyme activity was found from normal afferent, normal efferent, or stimulated efferent lymph cells. Afferent granuloma cells produced a plasminogen-dependent, DFP inhibitable protease activity that was dependent on the cell concentration and the incubation time. Results of cell separation techniques such as sedimentation velocity, adherence on fibrin plates, and Sephadex G-10 fractionation showed that the large, macrophage-like cell population in afferent lymph was secreting the plasminogen activator. The lymph cells collected from lesions 1 to 2-mo-old were more active than an equivalent number of cells collected from earlier or later lesions. When tuberculin was injected directly into lesions the lymph cells that appeared in the subsequent 1 to 2 days produced more enzyme per cell. The relationship between plasminogen activator and other possible mediators that appear in either the cells or plasma of afferent lymph is discussed.

Lymphocyte traffic through chronic inflammatory lesions: differential migration versus differential retention.

Afferent lymphatics draining granulomas and efferent lymphatics from normal lymph nodes were cannulated in sheep. Cells collected from these lymphatics were radiolabelled in vitro with 111In (afferent lymph cells) and 51Cr (efferent lymphocytes) and both labelled cells were returned to the animal simultaneously by i.v. injection. The reappearance of these labelled cells in lymph, and the amount of 111In and 51Cr in normal or antigenically stimulated lymph nodes, cutaneous inflammatory sites (FCA-granulomas, NLT- and BCG-induced lesions) and blood was determined 24 hr later. As previously reported, labelled afferent cells preferentially migrated from the blood back through the granuloma into afferent lymph, and efferent lymphocytes back into efferent lymph. Forty per cent as many 111In- as 51Cr-labelled cells ;appeared in efferent lymph. This was caused by the greater migration of 51Cr-labelled cells appeared in efferent lymph. This was caused by the greater migration of 51Cr- than 111In-labelled cells out of the blood into the node. Neither cell type was selectively retained in the node, and 28% of the labelled cells that entered the node migrated on into efferent lymph in 24 hr. Similarly, there was no selective retention of either cell type in the granuloma, and equal amounts of 111In the 51Cr appeared in afferent lymph. The ratio 111In/51Cr in the blood suggested that in the lymph node the two labelled cell populations were extracted equally, while in the granuloma selectively at the level of the vascular endothelium resulted in the preferential extraction of 111In-labelled (afferent lymph) cells.