The migration of lymphocytes across specialized vascular endothelium: VIII. Physical and chemical conditions influencing the surface morphology of lymphocytes and their ability to enter lymph nodes

Analyzing the migration of labeled T cells in vivo: an essential approach with challenging features

T cells are involved in the pathogenesis of many diseases. To exert a pathological effect, T cells enter the tissues. We show that the determination of their entry site requires isolation of the respective T cell population, injection into genetically un-manipulated animals, and identification of the cells in vivo at various time points after injection. We indicate variables influencing in vivo migration experiments artificially, and outline how resulting problems can be either avoided or taken into account. Reviewing experiments performed according to the outlined criteria reveals two types of migration patterns for T cell subsets in vivo: 1). Naïve and memory T cells enter lymphoid and non-lymphoid organs in comparable numbers, but selectively accumulate in lymphoid tissues over time, 2). Effector T cells, too, enter lymphoid and non-lymphoid organs in comparable numbers. However, most of them die within 24 hours. Depending on the presence of cytokines, chemokines and extracellular matrix compounds they are able to survive, thereby preferentially accumulating in their target tissues. This information might help to understand the role of migration in the pathogenesis of T cell mediated diseases.

Lymphocyte trafficking: CD4 T cells with a 'memory' phenotype (CD45RC-) freely cross lymph node high endothelial venules in vivo

Antigen encounter not only induces a change in surface expression of CD45RC isoforms in the rat from a high (CD45RC+) to a low molecular weight molecule (CD45RC-), but also stimulates changes in expression of adhesion molecules that regulate CD4 T-cell migration. T cells with an activated or 'memory' phenotype (CD45RC-) are thought to enter lymph nodes almost exclusively via afferent lymphatics whereas T cells in a resting state (CD45RC+) migrate across high endothelial venules (HEV). The present study monitored the rapid recirculation from blood to lymph of allotype-marked CD45RC T-cell subsets. Surprisingly, we found that CD45RC- CD4 T cells entered the thoracic duct slightly faster and reached peak numbers 3 hr earlier (18 hr) than did the CD45RC+ subset. To determine whether the entrance of CD45RC+ and RC- subsets was restricted to HEV and afferent lymphatics, respectively, recirculation of CD4 T cells was monitored in mesenteric lymphadenectomized (MLNx) rats (on healing the intestinal afferent lymphatics are joined directly to the thoracic duct), or in recipients that had had the mesenteric lymph node (MLN) acutely (2-3 hr) deafferentized (entry would be restricted to HEV). In these studies CD45RC- CD4 T cells entered the MLN across HEV on an equal basis with T cells expressing a CD45RC+ phenotype. Contrary to currently held dogma the results showed that, in vivo, CD4 T cells with a memory phenotype freely enter lymph nodes (LN) across HEV as well as via afferent lymphatics.

Interaction of B and T lymphocyte subsets with high endothelial venules in the rat: binding in vitro does not reflect homing in vivo

Lymphocytes continuously migrate through the body, and their efficient extravasation from the blood via high endothelial venules (HEV) is essential for initiating an appropriate immune response. Most investigations have focused on the lymphocyte/HEV interaction in vitro. However, to what extent such systems reflect the situation in vivo is not known. It is also unclear whether lymphocyte subsets immigrate into the HEV in proportion to their presence in the blood, and whether import capacity is limited by the HEV. When rat mesenteric lymph node lymphocytes were incubated in vitro on cryostat sections, the well-known preferential binding of B lymphocytes to HEV of Peyer's patches (PP) and T cells to HEV of axillary lymph nodes (axLN) was observed (axLN vs. PP: B lymphocytes 21.2 +/- 5.0% vs. 40.6 +/- 11.0%, T lymphocytes 84.6 +/- 6.3% vs. 56.5 +/- 12.9%). However, when labeled mesenteric lymph node lymphocytes were injected and their location within the HEV was analyzed 15 min later, no preferential interaction was seen. After injection of labeled thoracic duct lymphocytes, the percentage of labeled cells among B and T lymphocytes in the blood was significantly different (4.4 +/- 0.9% vs. 8.9 +/- 3.6%), whereas that in HEV of axLN (19.0 +/- 6.4% vs. 16.6 +/- 6.0%) and PP (30.6 +/- 6.1% vs. 33.9 +/- 4.4%) was comparable. Although the number of injected lymphocytes was similar in magnitude to the total blood lymphocyte pool, after injection there was no increase in lymphocyte numbers in the HEV. Thus, the adhesion assay in vitro does not completely reflect immigration into HEV in vivo. In addition, our data suggest that both the availability of lymphocyte subsets in small venules and the immigration rate into HEV are actively regulated in vivo.

Membrane CD45R isoform exchange on CD4 T cells is rapid, frequent and dynamic in vivo

CD4 T cells bearing high (240-190 kDa) and low (180 kDa) molecular mass isoforms of the leukocyte common antigen CD45 define functionally distinct subsets which have been equated with naive and memory T cells. In the rat, CD4 T cells expressing a high molecular mass isoform [identified by monoclonal antibody MRC-OX22 (anti-CD45RC)] exchange this for the 180 kDa molecule (CD45RC-) when stimulated by antigen. Here we show, by transferring mature allotype-marked CD45RC- CD4 T cells (depleted of immature Thy-1+ CD45RC- recent thymic emigrants) into normal euthymic recipients, that many T cells re-express the high molecular mass isoform in less than 6 h. By 24 h, 30-60% of CD45RC- CD4 T cells became CD45RC+; within a week the entire cohort appeared to exchange the low for the high molecular mass isoform. Isoform exchange was dynamic and many CD4 T cells returned once again to the CD45RC- state. CD45RC- CD4 T cells declined in number more rapidly than the CD45RC+ subset after transfer. The results suggest that CD45R isoforms distinguish between resting T cells (CD45RC+) and those which have encountered antigen in the recent past. CD45R isoforms would appear to be unsuitable markers of naive and memory T cells.

Random entry of circulating lymphocyte subsets into peripheral lymph nodes and Peyer's patches: no evidence in vivo of a tissue-specific migration of B and T lymphocytes at the level of high endothelial venules

Lymphocytes continuously migrate through the body and thus immune competent cells are constantly delivered to most tissues. They interact with high endothelial venules (HEV) via specific homing receptors and vascular addressins, and these molecules seem to be the reason for a preferential homing of B lymphocytes into Peyer's patches and of T lymphocytes into peripheral lymph nodes. When lymphocytes derived from lymph node cell suspensions were applied in the in vitro lymphocyte/endothelium binding assay, the well-known preference of mouse lymph node B lymphocytes for Peyer's patch HEV compared to peripheral lymph node HEV was confirmed in the rat (2.8 times). When in the same in vitro assay thoracic duct lymphocytes (TDL) were used this preference was far less obvious (1.4 times). However, by injecting rat TDL intravenously and by tracing them directly in HEV, B, T, CD4+ and CD8+ lymphocytes are seen to enter Peyer's patches and peripheral lymph nodes in vivo without preference. Thus, in contrast to lymphocytes from lymph node cell suspensions, no evidence was found of a tissue-specific migration of thoracic duct B, T, CD4+ and CD8+ lymphocytes at the HEV level. This finding demonstrates the importance of considering both experimental conditions and the cell source used when investigating lymphocyte traffic.

The "in situ" immune response in lymph nodes: a review

For many years data on the development of specific antibody-forming cells in lymph nodes were incomplete, fragmentary, and even contradictory. A number of recent studies have been performed, concerning 1) their overall architecture; 2) migration of B-lymphocytes; 3) localization of accessory cells and T-lymphocytes which are believed to be involved in humoral immune responses; and 4) localization patterns of specific antibody-forming cells developing during thymus dependent and thymus independent immune responses. Comparison of these new results with those of earlier studies suggests a single route of migration followed by all cells which will differentiate into antibody-forming cells. During their differentiation into antibody-forming plasma cells, antigen reactive B-cells migrate along the required accessory cells and/or T-lymphocytes.

A new method for rapid technetium-99m labelling of leucocytes: functional cell studies in vitro

The aim of this study was to assess the cytotoxicity of a new leucocyte-labelling method, which may be used clinically to localize inflammatory and immune reactions. Human blood leucocytes, their mononuclear sub-population, and mouse mononuclear bone marrow cells were labelled with 99mTc for 30-45 min, washed once, and then evaluated in various functional assays. The new procedure includes [99mTc]-labelling with a bisalt method, in the presence of dihydroxybenzoic acid as an intermediate antioxidant-complexing stabilizer, and a carboxylic acid salt of stannous ions as a reducing agent. To challenge the method, cells were labelled about two orders of magnitude more heavily in these initial methodological studies than in on-going clinical trials. Labelled leucocytes ingested latex beads as readily as the controls, but migrated chemotactically and randomly somewhat slower than the control cells. The lymphocytes were triggered by PHA and Con A in a normal way. However, lymphocytes and haemopoietic progenitor cells exposed to radiation for several days, were killed by the isotope doses used, of which about 2% (i.e. 20 MBq) were bound per million cells. All deleterious effects were apparently due to irradiation, and the labelling procedure itself did not damage the cells.

Functional and morphological changes in post-capillary venules in relation to lymphocytic infiltration into BCG-induced granulomata in rat skin

Vessels identical to lymph node high endothelial venules (HEV) have been described in sites of non-lymphoid tissue lymphocyte accumulation. In this study the function of these (HEV-like) vessels has been investigated in BCG-induced skin lesions in the rat. By following the traffic of radiolabelled lymphocytes from the blood into the lesions the HEV-like vessels have been shown to be the preferred site of migration. The complicated development of the vessels has been studied and an hypothesis advanced to explain their inter-relationship with tissue and circulating lymphocytes.

The organization of cell populations within lymph nodes: their origin, life history and functional relationships

The normal lymph node comprises a superficial cortex, a deep cortex or paracortex and a medulla. In each of these regions there are three kinds of spaces: an intralymphatic space, an intravascular space and an extravascular space or interstitium. Both the vascular endothelium and the lymphatic endothelium are specialized in these different regions. The cell types in lymph nodes comprise lymphoid cells, accessory or non-lymphoid cells and stromal cells, and within these cell types a number of different sub-types can now be identified by means of enzyme- and immunocytochemistry. Based predominantly on experimental studies, the origin, migratory patterns, localization, inter-relationships and interactions between these various cells are reviewed.

Afferent lymph and lymph borne cells: their influence on lymph node function

In AO rats the afferent lymphatics to the right cervical lymph nodes (LN) were interrupted and the LN were encased in silicone rubber tubes to prevent reunion of the lymphatics. At regular intervals over the next 12 weeks the following were measured in comparison with the intact contralateral LN - LN weight, influx of lymphocytes from the blood, blood flow, the incorporation of 125IUdR and the incorporation of 35S-sulphate into high endothelial venules (HEV). Systematic histological observations are also reported. One day after deafferentization lymphocyte influx was significantly reduced although blood flow was unchanged and a temporary increase in LN weight was associated with crowding of the lymphatic sinuses with small lymphocytes. The subsequent decline in lymphocyte influx was biphasic and quicker than the decline of other parameters--being undetectable by 6 weeks. Flattening of HEV and diminished secretion of 35S-sulphate was noted at 1 week and progressive degeneration and eventual disappearance of the HEV network was seen by 6-12 weeks. Doubtlessly because of lack of antigenic stimulation 125IUdR incorporation, and numbers of lymphoblasts, plasma cells and finally germinal centres were progressively reduced. The numbers of macrophages and interdigitating cells (IDC) were greatly reduced by 3 weeks and very few were present at 6 weeks probably because most or all arrive in afferent lymph and have a limited life span in the LN. At 12 weeks the LN was difficult to recognize as such since only stromal cells and occasional small lymphocytes remained. In supplementary experiments u.v. irradiation of the LN at the time of deafferentization reduced lymphocyte influx without affecting blood flow suggesting that a u.v. sensitive cell like the IDC may influence lymphocyte influx. In conclusion the involution of the deafferentized LN is partly due to the lack of antigen but progression to the complete loss of specialized structure and function is probably due to lack of other factors including non-lymphoid cells that normally arrive in afferent lymph.