The recirculation of naive and memory lymphocytes

Tissue localization and frequency of antigen-specific effector CD4 T cells determines the development of allergic airway inflammation

Previous activation of effector Th2 cells is central to the development of allergic inflammatory responses. We have observed that priming of allergen-specific Th2 cells in C57BL/6 or B10.A mice with allergen delivered via the i.p. or s.c. routes results in very different outcomes following subsequent airway exposure to the same allergen. Systemic allergen immunization (via the i.p. route) resulted in the formation of a lung-resident population of allergen-specific T cells, and mice developed severe allergic airway inflammation in response to inhaled allergen. The localization of cells to the lung did not require the presence of antigen at this site, but reflected a large pool of circulating activated allergen-specific T cells. In contrast, localized immunization (via the s.c. route) resulted in a small T-cell response restricted to the draining lymph node, and mice were not responsive to inhaled allergen. These data indicate that prior sensitization to an allergen alone was not sufficient for the induction of allergic inflammation; rather, responsiveness was largely determined by precursor frequency and tissue localization of the allergen-specific effector Th2 cells.

Technetium-99m scintigraphy to visualize T-cell homing in vivo: a preclinical study

The knowledge of lymphocyte distribution is very usefulness in monitoring therapeutic treatments. We present here a method employed in clinical practice, the scintigraphy, to study in the rat the physiologic lymphocyte traffic. Rat T cells labeled with 99mTc were injected in syngeneic animals, and their fate was studied by serial scintigraphic scanning. Sorted naïve CD4+ CD45RC(bright) T cells homed to lymphoid organs and accumulated in spleen. CD4+ CD45RC(dim) memory lymphocytes first reached the liver and the lungs and recirculated. The results obtained by using the scintigraphic method to in vivo study the lymphocyte homing in rats are comparable to those obtained with previously used experimental methods. We consider the scintigraphic method a useful tool to in vivo track lymphocytes and to address therapeutic treatment in men.

IFN-gamma reverses the stop signal allowing migration of antigen-specific T cells into inflammatory sites

In humans the majority of endothelial cells (EC) constitutively express MHC class II Ags. We know that in vitro ECs can activate CD45RO(+) B7-independent CD4(+) T cells to proliferate and produce IL-2. The in vivo correlate of this T cell response is not known, and here we have explored whether endothelial expression of MHC class II Ags affects the transendothelial migration of alloreactive CD4(+) CD45RO(+) B7-independent T cells. Alloreactive CD4(+) T cell clones and lines were generated against HLA-DR11, DR13, DR4, and DR1 MHC Ags, and their rates of migration across untreated EC line Eahy.926 (MHC class II negative) or Eahy.926 transfected with CIITA (EahyCIITA) to express DR11 and DR13 were investigated. The migrations of EahyCIITA-specific T cell clones and lines were retarded in a DR-specific manner, and retardation was reversed in the presence of mAb to DR Ag. When investigating the ability of T cells to proliferate in response to EahyCIITA before and after transmigration, migrated cells were still able to proliferate, but the frequency of EahyCIITA-specific cells was much reduced compared with that of nonmigrated cells. The use of fluorescently labeled T cells revealed that specific cells become trapped within the endothelial monolayer. Pretreatment of EahyCIITA with IFN-gamma restored the ability of DR11- or DR13-specific T cells to transmigrate and proliferate, thus abrogating DR-specific retardation. We conclude that cognate interaction between T cells and endothelial MHC class II initiates a stop signal possibly similar to an immunological synapse, but this is overcome in an inflammatory milieu.

Regulation of TIMP-1 phenotypic expression in Epstein--Barr virus-immortalized B lymphocytes

Normal B lymphocytes as well as malignant B cells extravasate from blood circulation during physiological and pathological processes and require matrix metalloproteinases (MMPs) to facilitate trafficking through the subendothelial basal lamina and the extracellular matrix. We have previously shown that Epstein-Barr virus (EBV)-immortalized B lymphocytes constitutively synthesized low levels of MMP-9 and huge amounts of its preferential inhibitor, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1). In the present study, TIMP-1 phenotypic expression was extensively investigated in response to various mediators including interleukins, chemokines, growth factors and tumor promotor, and was compared to MMP-9 synthesis. Results showed a roughly constitutive TIMP-1 expression opposed to an inducible MMP-9 synthesis. Nevertheless, further analysis of TIMP-1 synthesis showed the existence of regulation mechanisms: modulation of intracellular Ca(2+) concentration as well as cation ionophore monensin were demonstrated to influence TIMP-1 production and secretion. The precise pathways implicated in these regulation mechanisms are currently under survey.

Differential expression of beta1 and beta2 integrins and L-selectin on CD4+ and CD8+ T lymphocytes in human blood: comparative analysis between isolated cells, whole blood samples and cryopreserved preparations

Flow cytometric analysis was used to compare the expression of adhesion molecules on human CD4+ and CD8+ T lymphocytes in isolated blood mononuclear cells (MNCs) in whole blood samples and in cryopreserved MNC preparations. Examination of MNCs revealed that the CD11b and CD11c components of the beta2 integrins were preferentially expressed on CD8+ T cells, whereas CD62L was present on more CD4+ T cells. All CD4+ and CD8+ T lymphocytes were positive for CD11a but the CD8+ population had a higher intensity of expression of CD11a and also CD11b. Virtually identical results were obtained with T cells in whole blood samples. In relation to the beta1 integrins, the only difference between isolated CD4+ and CD8+ T cells was that the latter subset had a greater proportion of cells bearing CD49d. The naive cell marker CD45RA was present on the majority of CD8+ T cells whereas CD45RA and the memory marker CD45RO were evenly distributed within the CD4+ T cell subset. Although cryopreservation of lymphocytes did not modify the expression of beta1 and beta2 integrins it produced a marked reduction in the percentage of CD4+ and CD8+ T cells bearing CD62L. With regard to endothelial interactions, it appears that cryopreserved lymphocytes are suitable for inclusion in studies of integrin-mediated adhesion but not for those relating to tethering or recognition of addressins on high endothelial venules. Differences in adhesion molecule expression between CD4+ and CD8+ T lymphocytes could underlie the selective extravasation of these subsets into sites of infection and inflammation.

Flow cytometric assessment of lymphocyte subsets, lymphoid progenitors, and hematopoietic stem cells in allogeneic stem cell grafts

Currently, bone marrow (BM), cord blood (CB), and G-CSF-mobilized peripheral blood progenitor cells (PBPCs) are the most commonly used sources for allogeneic stem cell transplantation (SCT). The aim of this study was to assess the yields and distribution of lymphocyte subsets, lymphocyte progenitors and hematopoietic stem cells (HSC) in each type of allograft by three-color flow cytometry. The yields of CD34(+)CD38(-) HSCs did not differ significantly between BM grafts (2.80 +/- 0.74 x 10(6)) and leukapheresis products (LPs) (1.82 +/- 0.64 x 10(6)), and were lowest in CB grafts (0.21 +/- 0.05 x 10(6)). For most lymphocyte subsets yields were lowest in CB grafts and significantly higher in LPs than in BM grafts. BM grafts, however, contained the highest yields of CD34(+)CD19(+)CD20(-) B cell progenitors and CD19(+)CD20(-) B cells. The relative frequencies of the naive CD45RA(+)CD45RO(-) phenotype among CD4(+) and CD8(high) T cells were highest in CB grafts (P < or = 0.001), and higher in LPs than in BM grafts (P < or = 0.02). The latter finding was in accordance with a preferential G-CSF mobilization of naive T cells relative to the total lymphocyte population (P < or = 0.014). CD3(+)CD8(low) and CD3(+)CD8(low)CD4(-) subsets, which facilitate engraftment in murine transplantation models, demonstrated a tendency towards lower frequencies among T cells in CB grafts and LPs compared to BM grafts. This observation coincided with a significantly reduced mobilization of subsets potentially enriched for facilitating cells as compared to the total lymphocyte population (P < or = 0.036). The CD34(+) compartment of CB grafts contained a significantly higher percentage (12.1%) of CD34(+)CD7(+)CD3(-) T cell progenitors than those of BM grafts (5.1%) and LPs (3.6%). In addition, CB lymphocytes contained the highest fraction of CD3(-)CD16/56(+) NK cells (P < or = 0.013) and almost no CD3(+)CD16/56(+) NKT cells (P < 0.001) compared to adult cell sources. In summary, LPs, CB allografts and BM allografts differ widely with respect to the cellular composition of their lymphocyte compartments, which is partially affected by a varying mobilization efficiency of G-CSF for distinct lymphocyte subsets.

BDCA-2, BDCA-3, and BDCA-4: three markers for distinct subsets of dendritic cells in human peripheral blood

We have generated a panel of mAbs that identify three presumably novel human dendritic cell Ags: BDCA-2, BDCA-3, and BDCA-4. In blood, BDCA-2 and BDCA-4 are expressed on CD11c(-) CD123(bright) plasmacytoid dendritic cells, whereas BDCA-3 is expressed on small population of CD11c(+) CD123(-) dendritic cells. All three Ags are not detectable on a third blood dendritic cell population, which is CD1c(+) CD11c(bright) CD123(dim), or on any other cells in blood. BDCA-4 is also expressed on monocyte-derived and CD34(+) cell-derived dendritic cells. Expression of all three Ags dramatically changes once blood dendritic cells undergo in vitro maturation. BDCA-2 is completely down-regulated on plasmacytoid CD11c(-) CD123(bright) dendritic cells, expression of BDCA-3 is up-regulated on both plasmacytoid CD11c(-) CD123(bright) dendritic cells and CD1c(+) CD11c(bright) CD123(dim) dendritic cells, and expression of BDCA-4 is up-regulated on CD1c(+) CD11c(bright) CD123(dim) dendritic cells. BDCA-2 is rapidly internalized at 37 degrees C after mAb labeling. The three presumably novel Ags serve as specific markers for the respective subpopulations of blood dendritic cells in fresh blood and will be of great value for their further analysis and to evaluate their therapeutic potential.

A role for the cell adhesion molecule CD44 and sulfation in leukocyte-endothelial cell adhesion during an inflammatory response?

CD44 is a widely expressed cell adhesion molecule that has been implicated in a variety of biological processes including lymphopoiesis, angiogenesis, wound healing, leukocyte extravasation at inflammatory sites, and tumor metastasis. The adhesive function of CD44, like other molecules involved in inducible adhesion, is tightly regulated. Post-translational modifications, isoform expression, aggregation state, and protein associations all can affect the ligand binding properties of CD44, and these can vary depending on the cell type and the activation state of the cell. The most extensively characterized ligand for CD44 is hyaluronan, a component of the extracellular matrix. Interactions between CD44 and hyaluronan can mediate both cell-cell and cell-extracellular matrix adhesion. In the immune system, both the selectin molecules and CD44 have been implicated in the initial binding of leukocytes to endothelial cells at an inflammatory site. Sulfation is required for selectin-mediated leukocyte-endothelial cell interactions, and, recently, inducible sulfation also was shown to regulate CD44-mediated leukocyte adhesion to endothelial cells. Sulfation, therefore, may be important in the regulation of cell adhesion at inflammatory sites. In this commentary we have reviewed the molecular aspects of CD44 and the mechanisms that regulate its binding to hyaluronan. In addition, we have summarized the role of CD44 and hyaluronan in mediating leukocyte-endothelial cell interactions and have discussed how this interaction may be regulated. Finally, we examined the potential role of sulfation as an inducible means to regulate CD44-mediated leukocyte adhesion and as a more general mechanism to regulate leukocyte-endothelial cell interactions.

Memory CD4 cells do not migrate into peripheral lymphnodes in the absence of antigen

Memory T cells are thought to protect against previously encountered pathogens in part by preferentially recirculating through the lymphoid tissues where they were primed and where challenge with antigen (Ag) is likely to occur. In this study, we examined the distribution of memory CD4 cells after priming, and analyzed their capacity to localize in lymph nodes after transfer to normal and Ag-primed recipients. Immunization induced a high frequency of Ag-specific CD4 cells in the primary response in draining lymph nodes and spleen. Thereafter, the numbers in lymph nodes declined dramatically whereas frequencies in the spleen were unchanged, suggesting that memory CD4 cells primarily reside in or recirculate through the spleen. Indeed, memory CD4 cells, unlike naive CD4 cells, failed to home to lymph nodes after adoptive transfer to normal recipients and were detected predominantly in the spleen for extended periods, suggesting that recirculation through lymph nodes was limited. Memory cells also did not home to lymph nodes recipients in response to specific Ag, but subsequently, recruitment that could be blocked with monoclonal antibodies to CD44 and LFA-1 and was independent of naive cells did occur. The data indicate that memory and naive CD4 cells can be distinguished on the basis of their patterns of circulation.