The stromal scaffold of the lymph node (LN) paracortex is built by fibroblastic reticular cells (FRCs). Conditional ablation of lymphotoxin-β receptor (LTβR) expression in LN FRCs and their ...mesenchymal progenitors in developing LNs revealed that LTβR-signaling in these cells was not essential for the formation of LNs. Although T cell zone reticular cells had lost podoplanin expression, they still formed a functional conduit system and showed enhanced expression of myofibroblastic markers. However, essential immune functions of FRCs, including homeostatic chemokine and interleukin-7 expression, were impaired. These changes in T cell zone reticular cell function were associated with increased susceptibility to viral infection. Thus, myofibroblasic FRC precursors are able to generate the basic T cell zone infrastructure, whereas LTβR-dependent maturation of FRCs guarantees full immunocompetence and hence optimal LN function during infection.
Display omitted
•Novel transgenic mouse model that targets FRCs in adult lymph nodes•FRC-specific ablation of the LTβR did not abrogate LN development•Myofibroblastic FRC precursors generate the basic infrastructure of the adult LN•LTβR-mediated FRC maturation is critical for the maintenance of immunocompentence
Fibroblastic reticular cells (FRCs) form the cellular scaffold of lymph nodes (LNs) and establish distinct microenvironmental niches to provide key molecules that drive innate and adaptive immune ...responses and control immune regulatory processes. Here, we have used a graph theory-based systems biology approach to determine topological properties and robustness of the LN FRC network in mice. We found that the FRC network exhibits an imprinted small-world topology that is fully regenerated within 4 wk after complete FRC ablation. Moreover, in silico perturbation analysis and in vivo validation revealed that LNs can tolerate a loss of approximately 50% of their FRCs without substantial impairment of immune cell recruitment, intranodal T cell migration, and dendritic cell-mediated activation of antiviral CD8+ T cells. Overall, our study reveals the high topological robustness of the FRC network and the critical role of the network integrity for the activation of adaptive immune responses.
A prominent activity of the chemokine system is the regulation of leukocyte trafficking. Here we summarize recent findings on the initial steps in chemokine receptor-induced signal transduction in ...leukocytes. In particular, we discuss the potential influences of the formation of oligomers of ligand and receptor and of coupling between chemokine signals and regulators of the cytoskeleton, such as small GTPases.
The overall composition of the mammalian intestinal microbiota varies between individuals: within each individual there are differences along the length of the intestinal tract related to host ...nutrition, intestinal motility and secretions. Mucus is a highly regenerative protective lubricant glycoprotein sheet secreted by host intestinal goblet cells; the inner mucus layer is nearly sterile. Here we show that the outer mucus of the large intestine forms a unique microbial niche with distinct communities, including bacteria without specialized mucolytic capability. Bacterial species present in the mucus show differential proliferation and resource utilization compared with the same species in the intestinal lumen, with high recovery of bioavailable iron and consumption of epithelial-derived carbon sources according to their genome-encoded metabolic repertoire. Functional competition for existence in this intimate layer is likely to be a major determinant of microbiota composition and microbial molecular exchange with the host.
Tissue-resident CD8
T cells (CD8
T
) populate lymphoid and non-lymphoid tissues after infections as first line of defense against re-emerging pathogens. To achieve host protection, CD8
T
have ...developed surveillance strategies that combine dynamic interrogation of pMHC complexes on local stromal and hematopoietic cells with long-term residency. Factors mediating CD8
T
residency include CD69, a surface receptor opposing the egress-promoting S1P1, CD49a, a collagen-binding integrin, and CD103, which binds E-cadherin on epithelial cells. Moreover, the topography of the tissues of residency may influence T
retention and surveillance strategies. Here, we provide a brief summary of these factors to examine how CD8
T
reconcile constant migratory behavior with their long-term commitment to local microenvironments, with a focus on epithelial barrier organs and exocrine glands with mixed connective-epithelial tissue composition.
Naive B cells use the chemokine receptor CXCR5 to enter B cell follicles, where they scan CXCL13-expressing ICAM-1
VCAM-1
follicular dendritic cells (FDCs) for the presence of antigen. ...CXCL13-CXCR5-mediated motility is mainly driven by the Rac guanine exchange factor DOCK2, which contains a binding domain for phosphoinositide-3,4,5-triphosphate (PIP3) and other phospholipids. While p110δ, the catalytic subunit of the class IA phosphoinositide-3-kinase (PI3K) δ, contributes to CXCR5-mediated B cell migration, the precise interdependency of DOCK2, p110δ, or other PI3K family members during this process remains incompletely understood. Here, we combined
chemotaxis assays and
imaging to examine the contribution of these two factors during murine naïve B cell migration to CXCL13. Our data confirm that p110δ is the main catalytic subunit mediating PI3K-dependent migration downstream CXCR5, whereas it does not contribute to chemotaxis triggered by CXCR4 or CCR7, two other chemokine receptors expressed on naïve B cells. The contribution of p110δ activity to CXCR5-driven migration was complementary to that of DOCK2, and pharmacological or genetic interference with both pathways completely abrogated B cell chemotaxis to CXCL13. Intravital microscopy of control and gene-deficient B cells migrating on FDCs confirmed that lack of DOCK2 caused a profound migration defect, whereas p110δ contributed to cell speed and directionality. B cells lacking active p110δ also displayed defective adhesion to ICAM-1; yet, their migration impairment was maintained on ICAM-1-deficient FDCs. In sum, our data uncover two complementary signaling pathways mediated by DOCK2 and p110δ, which enable CXCR5-driven naïve B cell examination of FDCs.
Although much is known about the physiological framework of T cell motility, and numerous rate-limiting molecules have been identified through loss-of-function approaches, an integrated functional ...concept of T cell motility is lacking. Here, we used in vivo precision morphometry together with analysis of cytoskeletal dynamics in vitro to deconstruct the basic mechanisms of T cell migration within lymphatic organs. We show that the contributions of the integrin LFA-1 and the chemokine receptor CCR7 are complementary rather than positioned in a linear pathway, as they are during leukocyte extravasation from the blood vasculature. Our data demonstrate that CCR7 controls cortical actin flows, whereas integrins mediate substrate friction that is sufficient to drive locomotion in the absence of considerable surface adhesions and plasma membrane flux.
The development of lymph nodes (LNs) and formation of LN stromal cell microenvironments is dependent on lymphotoxin-β receptor (LTβR) signaling. In particular, the LTβR-dependent crosstalk between ...mesenchymal lymphoid tissue organizer and hematopoietic lymphoid tissue inducer cells has been regarded as critical for these processes. Here, we assessed whether endothelial cell (EC)-restricted LTβR signaling impacts on LN development and the vascular LN microenvironment. Using EC-specific ablation of LTβR in mice, we found that conditionally LTβR-deficient animals failed to develop a significant proportion of their peripheral LNs. However, remnant LNs showed impaired formation of high endothelial venules (HEVs). Venules had lost their cuboidal shape, showed reduced segment length and branching points, and reduced adhesion molecule and constitutive chemokine expression. Due to the altered EC-lymphocyte interaction, homing of lymphocytes to peripheral LNs was significantly impaired. Thus, this study identifies ECs as an important LTβR-dependent lymphoid tissue organizer cell population and indicates that continuous triggering of the LTβR on LN ECs is critical for lymphocyte homeostasis.
Naïve T cells (T
) constitutively recirculate through secondary lymphatic organs (SLOs), where they scan dendritic cells (DCs) for cognate peptide-loaded major histocompatibility complexes (pMHC). ...Continuous trafficking between SLOs not only enables rapid clonal selection but also ensures T
homeostasis by providing access to prosurvival signals from TCR, IL-7R, and the chemokine receptor CCR7. Inside the lymphoid tissue, CCR7-mediated T
motility is mainly driven by the Rac activator DOCK2, with a separate contribution by a phosphoinositide-3-kinase γ (PI3Kγ)-dependent pathway. Tec tyrosine kinases and the Rac activator Tiam1 constitute prominent downstream effectors of PI3K signaling. Yet, the precise role of Tec kinase versus Tiam1 signaling during CCR7-mediated T
migration and homeostasis remains incompletely understood. Here, we examined the function of the Tec family member interleukin-2-inducible T-cell kinase (Itk) and Tiam1 during T
migration
and
using intravital microscopy. Itk deficiency caused a mild decrease in CCR7-triggered T
migration, mirroring observations made with PI3Kγ;
T cells, while lack of Tiam1 did not affect T
motility.
modeling suggested that reduced migration in the absence of Itk does not result in a substantial decrease in the frequency of T
encounters with DCs within the lymphoid tissue. In contrast, Itk was important to maintain
homeostasis of CD4
T
, also in MHCII-deficient hosts. Taken together, our data suggest that Itk contributes to T
migration and survival by integrating chemokine receptor and TCR signaling pathways.
Cell migration involves dynamic changes in cell shape. Intricate patterns of cell shape can be analyzed and classified using advanced shape descriptors, including spherical harmonics (SPHARM). Though ...SPHARM have been used to analyze and classify migrating cells, such classification did not exploit SPHARM spectra in their dynamics. Here, we examine whether additional information from dynamic SPHARM improves classification of cell migration patterns. We combine the static and dynamic SPHARM approach with a support-vector-machine classifier and compare their classification accuracies. We demonstrate that the dynamic SPHARM analysis classifies cell migration patterns more accurately than the static one for both synthetic and experimental data. Furthermore, by comparing the computed accuracies with that of a naive classifier, we can identify the experimental conditions and model parameters that significantly affect cell shape. This capability should - in the future - help to pinpoint factors that play an essential role in cell migration.
PDF
