7.1
Summary Paper I
Chu, H. et al. (2006). γ-Parvin is dispensable for hematopoiesis, leukocyte trafficking, and T- cell-dependent antibody response. Mol. Cell Biol. 26, 1817-25.
Parvins consist of three members (α-, β-, γ-parvin) which are components of a multiprotein complex that assembles at the cytoplasmic domain of integrin receptors at sites of cell adhesion. Together with integrin-linked kinase (ILK) and PINCH, parvins form a functional complex that links integrins to the cytoskeleton. While α- and β-parvins are widely expressed, γ-parvin has been reported to be restricted to hematopoietic cells. In this study, the expression pattern of the parvins in hematopoietic cells and the phenotype of γ-parvin-deficient mice were analyzed. Mice lacking γ-parvin were viable and fertile. Surprisingly, loss of γ-parvin expression had no effect on blood cell differentiation, proliferation, and survival and no consequence for the T-cell-dependent antibody response and for the migration of lymphocytes and dendritic cells. These data indicate that despite high expression of γ-parvin in hematopoietic cells it must play a more subtle role for blood cell homeostasis.
I contributed to this study by assisting in leukocyte homing assays and flow cytometry analysis of apoptosis.
7.2
Summary Paper II (Review)
Sixt, M. et al. (2006). β1 integrins: zip codes and signaling relay for blood cells. Curr. Opin. Cell Biol. 18, 882-90.
β1 integrins comprise the largest integrin receptor family. At least eight of the twelve known heterodimers of the β1 integrin family are expressed on hematopoietic cells. Among these, the VCAM-1 receptor α4β1 has been studied most thoroughly during the process of blood cell extravasation. In this review, we summarize and discuss the confirmed and speculative roles of β1 integrins in leukocyte extravasation, transmigration, movement and retention in interstitial tissues and cell-cell interactions between immune cells. We further give a short overview how targeting integrin interactions might be beneficial in anti-inflammatory therapies.
Brief summaries of the publications
7.3
Summary Paper III (Review)
Lokmic, Z.*, Lämmermann, T.* et al. (2006). The extracellular matrix of the spleen as a
potential organizer of immune cell compartments. Sem. in Immunol. 20, 4-13.
* equally contributing first authors.
Blood cells and blood-derived pathogens constantly pass through the open vascular system of the spleen. To exert its dual role as secondary lymphoid organ and site of erythrocyte removal, the spleen is highly organized into different compartments (white pulp, red pulp and marginal zone). While their immune cell composition has been studied in detail over the years, the fibroblastic reticular cell network has only gained little attention. This stromal backbone consists of reticular fibroblasts and extracellular matrix (ECM). In this review, we summarize how distinctly expressed ECM molecules define splenic compartments and speculate about their impact on immune cell localization and structural support. In particular, we highlight the unique molecular structure of the reticular fiber network in the white pulp that, as in the T cell cortex of the lymph node, serves as a conduit for fluid and small particle transport.
7.4
Summary Paper IV (Review)
Lämmermann, T. and Sixt, M. (2008). The microanatomy of T-cell responses. Immunol. Rev. 221, 26-43.
Soluble and cell-bound antigens are delivered from the periphery through lymphatic vessels into the lymph node where they initiate adaptive immune responses. In this review, we describe the non-hematopoietic infrastructure of the lymphatic system with a focus on antigen transport from the skin to the draining lymph node. Dendritic cells (DCs) are the major antigen-presenting cells in the periphery. After antigen uptake, they migrate in the dermis, enter the lymphatic vessels and pass the subcapsular sinus of the lymph node. In the cortex, they meet T cells that move along the fibroblastic reticular cell (FRC) network, the stromal backbone of secondary lymphoid organs. Here, we describe the functional anatomy of these compartments and the molecular requirements for DC migration. In contrast to cell-bound antigen, soluble antigen is rapidly transported by dermal fluid to the lymph node where it is directly drained into the inner core of the FRC network serving as conduit system. We discuss the molecular similarities between the conduit system and the dermis and suggest that the
Brief summaries of the publications
7.5
Summary Paper V
Lämmermann, T. et al. (2008). Rapid leukocyte migration by integrin-independent flowing and squeezing. Nature. 453, 51-55.
According to the general cell migration paradigm, locomoting cells generate traction by coupling contractile forces and actin polymerization to an adhesive surface. In agreement with this principle, rapidly migrating leukocytes use integrin-mediated adhesion when moving over two-dimensional surfaces or along blood vessels. By contrast, the contribution of integrins during three-dimensional (3D) movement of leukocytes within tissues has remained controversial. While blocking integrin function with antibodies might have produced unspecific side effects, single genetic depletion of integrin subunits could not rule out a compensating role for other integrin heterodimers. In this study, we genetically ablated all integrin heterodimers from murine leukocytes and show that functional integrins do not contribute to migration in 3D in vitro networks. By studying dendritic cell migration in the dermis, entry into the lymphatics and movement within the lymph node, we show that leukocyte migration in vivo is dispensable of integrins. Instead, leukocytes can migrate by the sole force of actin-network expansion, which promotes protrusive flowing of the leading edge. Myosin II-dependent contraction is only required upon passage through narrow gaps, where a squeezing contraction of the trailing edge propels the rigid nucleus. We conclude that non-adhesive migration renders leukocytes autonomous from the tissue context and allows them to quickly and flexibly navigate through any organ without adaptations to alternating extracellular ligands.
Acknowledgements
7.6 Summary Paper VI
Kessenbrock, K. et al. (2008). Proteinase 3 and neutrophil elastase enhance inflammation by inactivating anti-inflammatory progranulin. J. Clin. Invest.. 118, 2438-47.
Neutrophils represent the first line of defense during infectious inflammation, but also contribute to non-infectious chronic inflammation. In this study, mice that were depleted of two very similar neutrophil serine proteases, proteinase 3 (PR3) and neutrophil elastase (NE), showed reduced neutrophil infiltration in a model of subcutaneous formation of antigen- antibody immune complexes (Arthus reaction). This was not a generalized defect in neutrophil extravasation or migration, as neutrophil infiltration in response to application of phorbol esters to the skin and migration in a fibrillar interstitium was not impaired. Instead, NE and PR3 cleaved the anti-inflammatory molecule progranulin (PGRN) and administrating PGRN to wild-type mice inhibited neutrophil influx in the course of the Arthus reaction. In conclusion, NE and PR3 mediate local pro-inflammatory effects by degrading PGRN.
My contribution to this study was design and analysis of the phorbol ester-mediated inflammation model and analysis of neutrophil chemotaxis in 3D collagen gels.
7.7 Summary Paper VII
Lämmermann, T. et al. (2009). Cdc42-dependent leading edge coordination is essential for interstitial dendritic cell migration. Blood. Prepublished online February 3, 2009.
Interstitial leukocyte migration is independent of adhesive forces and pericellular proteolysis. Instead, the protrusive flow of the actin cytoskeleton directly drives a basal mode of locomotion that is occasionally supported by actomyosin contractions at the trailing edge to propel the cell’s rigid nucleus. In this study, we address the question how coordination of actin flow influences leukocyte migration in a three-dimensional (3D) environment. We employed DCs lacking the small GTPase Cdc42 that still initiated actin flow and actomyosin contraction in response to chemotactic cues, but failed to temporally and spatially regulate their protrusions. While this defect still allowed the cells to move on two-dimensional surfaces, their in vivo motility was completely abrogated. This difference was entirely caused by the geometrical complexity of the environment as multiple competing protrusions led to instantaneous entanglement within 3D matrix scaffolds. We conclude that the decisive factor for migrating DCs is internal stabilization of polarity and adequate coordination of
Acknowledgements