Wendy L. Marston

Subset-Specific Regulation of the Lymphatic Exit of Recirculating Lymphocytes In Vivo

The blood-to-lymph recirculation of lymphocytes is required for the maintenance of immune surveillance and the dissemination of memory. Although the ability of lymph-borne cells to recirculate has been well documented, relatively less is known about the migration capacity of PBLs. We have found a clear preference for PBLs to recirculate through s.c. rather than intestinal lymph nodes. This preference could be directly attributed to the migratory characteristics of γδ-T cells. γδ-T cells were found to express significantly higher levels of L-selectin than other subsets, suggesting that at least some of this preferential migration could be attributed to their interaction with ligands on vascular endothelium. More detailed experiments showed that γδ-T cells migrated through lymph nodes with greater efficiency than αβ T cells or B cells, which clearly indicated an enhanced ability of γδ-T cells to exit lymph nodes in the efferent lymph independent of entry from the blood. This hypothesis was supported by histological examination, where γδ-T cells were found almost exclusively in the interfollicular traffic areas within lymph nodes. These data indicate that γδ-T cells are the most active recirculating lymphocyte subset in ruminants and suggest new mechanisms to regulate the traffic of lymphocyte subsets through normal lymph nodes.

A role for lymphatic endothelium in the sequestration of recirculating γ δ T cells in TNF‐α‐stimulated lymph nodes

TNF‐α is one of the most potent immunoregulatory molecules in vivo. In addition to important regulatory effects, it is also a potent inducer of extravascular lymphocyte infiltration. To examine the dynamic changes that are induced in local lymphocyte migration through regional lymph nodes following TNF‐α injection, we used a protocol of direct lymphatic cannulation to quantitatively and qualitatively examine the traffic of lymphocytes through regional lymph nodes. We observed that local TNF‐α injection reduced the output of lymphocytes from lymph nodes up to 90 % within 6 – 10 h following stimulation. TNF‐α also altered the specificity of migration of lymphocyte traffic through subcutaneous lymph nodes. In addition to the decreased output, phenotypic analysis demonstrated decreases in the concentration of γ δ T cells by up to 30 % following TNF‐α injection. Histological examination showed that the γ δ T cells were found in close association with VCAM‐1‐expressing cells in TNF‐stimulated lymph nodes, at least some of which appeared to be lymphatic endothelium. These data indicate that TNF‐α is capable of altering the number and specificity of lymphocytes recirculating through stimulated lymph nodes by selectively altering the entry of lymphocytes into the efferent lymphatics of inflamed lymph nodes in vivo.

Structure and expression of ovine complement receptor type 2

The structure of sheep complement receptor type 2 (CR2) was characterised by cDNA cloning, protein sequencing and immunoprecipitation. The primary structure of sheep CR2 is similar to known mammalian homologues but the higher-order structure is unusual. Two distinct CR2 isoforms occur, one of which is ubiquitinated in the cytoplasmic domain, and the two molecular forms are expressed at the cell surface as non-covalently associated dimers. The percentage of sheep B-cells that express CR2 changes during development and varies between different body compartments. CR2+ and CR2 B-cell subsets also differ in the expression of other surface markers and in functional properties. Differential expression of CR2 may, therefore, delineate B-cells that arose by alternative developmental pathways, or it could be a marker for B-cells at different phases of antigen exposure.

Expression of the “T19” and “null cell” markers on γδT cells of the sheep

Abstract A 215 kDa molecule termed T19 marks CD4−CD8− T cells in sheep and cattle. In this report, we analysed the T19 or “null cell” panel of mAbs against γδT cells of sheep, using a mAb specific for the γδTCR. By two-colour immunoflourescence, all of the mAbs in the T19 panel reacted with γδT cells or subsets thereof, although staining intensities and percentages of cells stained by the different mAbs indicated considerable heterogeneity for the T19 molecule. This probably results from differential expression of certain epitopes on T19. The reactivity of most of the mAbs ffor the 215 kDa T19 molecule was also confirmed by immunoprecipitation and SDS-PAGE.