Thomas G. Diacovo

Platelet-Mediated Lymphocyte Delivery to High Endothelial Venules

Circulating lymphocytes gain access to lymph nodes owing to their ability to initiate rolling along specialized high endothelial venules (HEVs). One mechanism of rolling involves L-selectin binding to peripheral node addressin (PNAd) on HEVs. Activated platelets are shown to bind to circulating lymphocytes and to mediate rolling in HEVs, in vivo, through another molecule, P-selectin, which also interacts with PNAd. In vitro, activated platelets enhanced tethering of lymphocytes to PNAd and sustained lymphocyte rolling, even in the absence of functional L-selectin. Thus, a platelet pathway operating through P-selectin provides a second mechanism for lymphocyte delivery to HEVs.

A functional integrin ligand on the surface of platelets: intercellular adhesion molecule-2.

Activated platelets express P-selectin and release leukocyte chemoattractants; however, they have not been known to express integrin ligands important in the stabilization of leukocyte interactions with the vasculature. We now demonstrate the presence of intercellular adhesion molecular-2 (ICAM-2) (CD102), and lack of expression of other beta 2-integrin ligands, ICAM-1 (CD54) and ICAM-3 (CD50), on the surface of resting and stimulated platelets. ICAM-2 isolated from platelets migrates as a band of 59,000 M(r) in reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Staining of bone marrow aspirates with anti-ICAM-2 mAb demonstrates strong reactivity to megakaryocytes. Using frozen thin sections and immunogold labeling, the antigen was shown to be present on the plasma membrane and surface-connected canalicular system of resting platelets. The average number of ICAM-2 molecules per platelet is 3,000 +/- 230 and does not change after activation. In adhesion assays, resting and stimulated platelets were capable of binding through ICAM-2 to purified leukocyte function-associated antigen-1. Activation of T lymphocytes with PMA stimulated binding to platelets that was Mg2+ dependent and could be specifically inhibited by mAbs to either ICAM-2 or leukocyte function-associated antigen-1. ICAM-2 is the only known beta 2-integrin ligand present on platelets, suggesting that it may play an important role in leukocyte-platelet interactions in inflammation and thrombosis.

Adhesive mechanisms governing interferon-producing cell recruitment into lymph nodes

Natural interferon-producing cells (IPCs) are found in peripheral lymph nodes (PLNs), where they support NK cell, T cell, and B cell responses to pathogens. However, their route of entry and the adhesive mechanisms used to gain access to PLNs remain poorly defined. We report that IPCs can enter PLNs via a hematogenous route, which involves a multistep adhesive process, and that transmigration is enhanced by inflammation. Results indicate that L-selectin on IPCs is required for efficient attachment and rolling on high endothelial venules in vivo in both nonstimulated and inflamed PLNs. IPCs, however, also possess functional ligands for E-selectin that contribute to this process only in the latter case. In conjunction with selectin-mediated adhesion, both β 1- and β 2-integrins participate in IPC attachment to the inflamed vessel wall, whereas chemotaxis relies in part on the chemokine receptor CCR5. Identification of the adhesive machinery required for IPC trafficking into PLNs may provide opportunities to regulate immune responses reliant on the activity of these cells.

Transendothelial chemotaxis of human αβ and γδ T lymphocytes to chemokines

Two subpopulations of human T lymphocytes expressing different antigen receptors, α / β and γ / δ, emigrate into inflamed tissues in distinctive patterns. We compared the transmigration of α / β and γ / δ T cells to C‐C and C‐X‐C chemokines using an in vitro transendothelial chemotaxis assay. The C‐C chemokines monocyte chemoattractant protein (MCP)‐1, RANTES, macrophage inflammatory protein (MIP)‐1α and MIP‐1β stimulated similar, dose‐dependent chemotaxis of purified γ / δ T cells, whereas MCP‐1, RANTES, and MIP‐1α pro duced greater chemotaxis of purified α / β T cells than MIP‐1β. In contrast, the C‐X‐C chemokines interleukin (IL)‐8 and interferon‐γ inducible protein‐10 (IP‐10) did not promote chemotaxis of either α / β or γ / δ T cells. Three γ / δ T cell clones with differing CD4 and CD8 phenotypes also migrated exclusively to C‐C chemokines. Phenotypic analysis of mononuclear cells that transmigrated from an input population of unfractionated peripheral blood mono nuclear cells confirmed the results with purified γ / δ T cells. Our data demonstrate that human peripheral blood α / β and γ / δ T cells can transmigrate to MCP‐1, RANTES, MIP‐1α, and MIP‐1β, and suggest that both T lymphocyte subpopulations share the capacity to emigrate in response to C‐C chemokines during inflammation.

Shedding light on class I phosphoinositide 3-kinase activity in endothelium.

To the editor: Class I phosphoinositide 3-kinases (PI3Ks) play a critical role in regulating chemoattractant-induced migration of neutrophils.[1][1] However, Puri et al have demonstrated that PI3K activity in vascular endothelium also contributes to the accumulation of these cells in tissues, as

A novel molecular interaction for the adhesion of follicular CD4 T cells to follicular DC: HIGHLIGHTS

Nectins and Nectin‐like molecules (Necl) play a critical role in cell polarity within epithelia and in the nervous and reproductive systems. Recently, immune receptors specific for Nectins/Necl have been described. Since the expression and distribution of Nectins/Necl is often subverted during tumorigenesis, it has been suggested that the immune system may use these receptors to recognize and eliminate tumors. Here we describe a novel immunoreceptor, Washington University Cell Adhesion Molecule, which is expressed on human follicular B helper T cells (TFH) and binds a Nectin/Necl family member, the poliovirus receptor (PVR), under both static and flow conditions. Furthermore, we demonstrate that PVR is abundantly expressed by follicular DC (FDC) within the germinal center. These results reveal a novel molecular interaction that mediates adhesion of TFH to FDC and provide the first evidence that immune receptors for Nectins/Necl may be involved the generation of T cell‐dependent antibody responses.

A novel molecular interaction for the adhesion of follicular CD4 T cells to follicular dendritic cells

Nectins and Nectin‐like molecules (Necl) play a critical role in cell polarity within epithelia and in the nervous and reproductive systems. Recently, immune receptors specific for Nectins/Necl have been described. Since the expression and distribution of Nectins/Necl is often subverted during tumorigenesis, it has been suggested that the immune system may use these receptors to recognize and eliminate tumors. Here we describe a novel immunoreceptor, Washington University Cell Adhesion Molecule, which is expressed on human follicular B helper T cells (TFH) and binds a Nectin/Necl family member, the poliovirus receptor (PVR), under both static and flow conditions. Furthermore, we demonstrate that PVR is abundantly expressed by follicular DC (FDC) within the germinal center. These results reveal a novel molecular interaction that mediates adhesion of TFH to FDC and provide the first evidence that immune receptors for Nectins/Necl may be involved the generation of T cell‐dependent antibody responses.