InVivoMAb anti-mouse Podoplanin (gp38) (Clone: 8.1.1)
Astarita, J. L., et al. (2015). "The CLEC-2-podoplanin axis controls the contractility of fibroblastic reticular cells and lymph node microarchitecture." Nat Immunol 16(1): 75-84. PubMed
In lymph nodes, fibroblastic reticular cells (FRCs) form a collagen-based reticular network that supports migratory dendritic cells (DCs) and T cells and transports lymph. A hallmark of FRCs is their propensity to contract collagen, yet this function is poorly understood. Here we demonstrate that podoplanin (PDPN) regulates actomyosin contractility in FRCs. Under resting conditions, when FRCs are unlikely to encounter mature DCs expressing the PDPN receptor CLEC-2, PDPN endowed FRCs with contractile function and exerted tension within the reticulum. Upon inflammation, CLEC-2 on mature DCs potently attenuated PDPN-mediated contractility, which resulted in FRC relaxation and reduced tissue stiffness. Disrupting PDPN function altered the homeostasis and spacing of FRCs and T cells, which resulted in an expanded reticular network and enhanced immunity.
Rouhani, S. J., et al. (2015). "Roles of lymphatic endothelial cells expressing peripheral tissue antigens in CD4 T-cell tolerance induction." Nat Commun 6: 6771. PubMed
Lymphatic endothelial cells (LECs) directly express peripheral tissue antigens and induce CD8 T-cell deletional tolerance. LECs express MHC-II molecules, suggesting they might also tolerize CD4 T cells. We demonstrate that when beta-galactosidase (beta-gal) is expressed in LECs, beta-gal-specific CD8 T cells undergo deletion via the PD-1/PD-L1 and LAG-3/MHC-II pathways. In contrast, LECs do not present endogenous beta-gal in the context of MHC-II molecules to beta-gal-specific CD4 T cells. Lack of presentation is independent of antigen localization, as membrane-bound haemagglutinin and I-Ealpha are also not presented by MHC-II molecules. LECs express invariant chain and cathepsin L, but not H2-M, suggesting that they cannot load endogenous antigenic peptides onto MHC-II molecules. Importantly, LECs transfer beta-gal to dendritic cells, which subsequently present it to induce CD4 T-cell anergy. Therefore, LECs serve as an antigen reservoir for CD4 T-cell tolerance, and MHC-II molecules on LECs are used to induce CD8 T-cell tolerance via LAG-3.
Dubrot, J., et al. (2014). "Lymph node stromal cells acquire peptide-MHCII complexes from dendritic cells and induce antigen-specific CD4(+) T cell tolerance." J Exp Med 211(6): 1153-1166. PubMed
Dendritic cells (DCs), and more recently lymph node stromal cells (LNSCs), have been described to tolerize self-reactive CD8(+) T cells in LNs. Although LNSCs express MHCII, it is unknown whether they can also impact CD4(+) T cell functions. We show that the promoter IV (pIV) of class II transactivator (CIITA), the master regulator of MHCII expression, controls endogenous MHCII expression by LNSCs. Unexpectedly, LNSCs also acquire peptide-MHCII complexes from DCs and induce CD4(+) T cell dysfunction by presenting transferred complexes to naive CD4(+) T cells and preventing their proliferation and survival. Our data reveals a novel, alternative mechanism where LN-resident stromal cells tolerize CD4(+) T cells through the presentation of self-antigens via transferred peptide-MHCII complexes of DC origin.
Fleige, H., et al. (2014). "IL-17-induced CXCL12 recruits B cells and induces follicle formation in BALT in the absence of differentiated FDCs." J Exp Med 211(4): 643-651. PubMed
Ectopic lymphoid tissue, such as bronchus-associated lymphoid tissue (BALT) in the lung, develops spontaneously at sites of chronic inflammation or during infection. The molecular mechanisms underlying the neogenesis of such tertiary lymphoid tissue are still poorly understood. We show that the type of inflammation-inducing pathogen determines which key factors are required for the formation and maturation of BALT. Thus, a single intranasal administration of the poxvirus modified vaccinia virus Ankara (MVA) is sufficient to induce highly organized BALT with densely packed B cell follicles containing a network of CXCL13-expressing follicular DCs (FDCs), as well as CXCL12-producing follicular stromal cells. In contrast, mice treated with P. aeruginosa (P.a.) develop BALT but B cell follicles lack FDCs while still harboring CXCL12-positive follicular stromal cells. Furthermore, in IL-17-deficient mice, P.a.-induced BALT largely lacks B cells as well as CXCL12-expressing stromal cells, and only loose infiltrates of T cells are present. We show that Toll-like receptor pathways are required for BALT induction by P.a., but not MVA, and provide evidence that IL-17 drives the differentiation of lung stroma toward podoplanin-positive CXCL12-expressing cells that allow follicle formation even in the absence of FDCs. Taken together, our results identify distinct pathogen-dependent induction and maturation pathways for BALT formation.
Pan, Y., et al. (2014). "Podoplanin requires sialylated O-glycans for stable expression on lymphatic endothelial cells and for interaction with platelets." Blood 124(24): 3656-3665. PubMed
O-glycosylation of podoplanin (PDPN) on lymphatic endothelial cells is critical for the separation of blood and lymphatic systems by interacting with platelet C-type lectin-like receptor 2 during development. However, how O-glycosylation controls endothelial PDPN function and expression remains unclear. In this study, we report that core 1 O-glycan-deficient or desialylated PDPN was highly susceptible to proteolytic degradation by various proteases, including metalloproteinases (MMP)-2/9. We found that the lymph contained activated MMP-2/9 and incubation of the lymph reduced surface levels of PDPN on core 1 O-glycan-deficient endothelial cells, but not on wild-type ECs. The lymph from mice with sepsis induced by cecal ligation and puncture, which contained bacteria-derived sialidase, reduced PDPN levels on wild-type ECs. The MMP inhibitor, GM6001, rescued these reductions. Additionally, GM6001 treatment rescued the reduction of PDPN level on lymphatic endothelial cells in mice lacking endothelial core 1 O-glycan or cecal ligation and puncture-treated mice. Furthermore, core 1 O-glycan-deficient or desialylated PDPN impaired platelet interaction under physiological flow. These data indicate that sialylated O-glycans of PDPN are essential for platelet adhesion and prevent PDPN from proteolytic degradation primarily mediated by MMPs in the lymph.
Herzog, B. H., et al. (2013). "Podoplanin maintains high endothelial venule integrity by interacting with platelet CLEC-2." Nature 502(7469): 105-109. PubMed
Circulating lymphocytes continuously enter lymph nodes for immune surveillance through specialized blood vessels named high endothelial venules, a process that increases markedly during immune responses. How high endothelial venules (HEVs) permit lymphocyte transmigration while maintaining vascular integrity is unknown. Here we report a role for the transmembrane O-glycoprotein podoplanin (PDPN, also known as gp38 and T1alpha) in maintaining HEV barrier function. Mice with postnatal deletion of Pdpn lost HEV integrity and exhibited spontaneous bleeding in mucosal lymph nodes, and bleeding in the draining peripheral lymph nodes after immunization. Blocking lymphocyte homing rescued bleeding, indicating that PDPN is required to protect the barrier function of HEVs during lymphocyte trafficking. Further analyses demonstrated that PDPN expressed on fibroblastic reticular cells, which surround HEVs, functions as an activating ligand for platelet C-type lectin-like receptor 2 (CLEC-2, also known as CLEC1B). Mice lacking fibroblastic reticular cell PDPN or platelet CLEC-2 exhibited significantly reduced levels of VE-cadherin (also known as CDH5), which is essential for overall vascular integrity, on HEVs. Infusion of wild-type platelets restored HEV integrity in Clec-2-deficient mice. Activation of CLEC-2 induced release of sphingosine-1-phosphate from platelets, which promoted expression of VE-cadherin on HEVs ex vivo. Furthermore, draining peripheral lymph nodes of immunized mice lacking sphingosine-1-phosphate had impaired HEV integrity similar to Pdpn- and Clec-2-deficient mice. These data demonstrate that local sphingosine-1-phosphate release after PDPN-CLEC-2-mediated platelet activation is critical for HEV integrity during immune responses.