CCR7 ligands stimulate the intranodal motility of T lymphocytes in vivo

In contrast to lymphocyte homing, little is known about molecular cues controlling the motility of lymphocytes within lymphoid organs. Applying intravital two-photon microscopy, we demonstrate that chemokine receptor CCR7 signaling enhances the intranodal motility of CD4+ T cells. Compared to wild-type (WT) cells, the average velocity and mean motility coefficient of adoptively transferred CCR7-deficient CD4+ T lymphocytes in T cell areas of WT recipients were reduced by 33 and 55%, respectively. Both parameters were comparably reduced for WT T lymphocytes migrating in T cell areas of plt/plt mice lacking CCR7 ligands. Importantly, systemic application of the CCR7 ligand CCL21 was sufficient to rescue the motility of WT T lymphocytes inside T cell areas of plt/plt recipients. Comparing the movement behavior of T cells in subcapsular areas that are devoid of detectable amounts of CCR7 ligands even in WT mice, we failed to reveal any differences between WT and plt/plt recipients. Furthermore, in both WT and plt/plt recipients, highly motile T cells rapidly accumulated in the subcapsular region after subcutaneous injection of the CCR7 ligand CCL19. Collectively, these data identify CCR7 and its ligands as important chemokinetic factors stimulating the basal motility of CD4+ T cells inside lymph nodes in vivo

Oral tolerance originates in the intestinal immune system and relies on antigen carriage by dendritic cells

Oral tolerance induction is a key feature of intestinal immunity, generating systemic nonresponsiveness to ingested antigens. In this study, we report that orally applied soluble antigens are exclusively recognized in the intestinal immune system, particularly in the mesenteric lymph nodes. Consequently, the initiation of oral tolerance is impeded by mesenteric lymphadenectomy. Small bowel transplantation reveals that mesenteric lymph nodes require afferent lymph to accomplish the recognition of orally applied antigens. Finally, oral tolerance cannot be induced in CCR7-deficient mice that display impaired migration of dendritic cells from the intestine to the mesenteric lymph nodes, suggesting that immunologically relevant antigen is transported in a cell-bound fashion. These results demonstrate that antigen transport via afferent lymphatics into the draining mesenteric lymph nodes is obligatory for oral tolerance induction, inspiring new therapeutic strategies to exploit oral tolerance induction for the prevention and treatment of autoimmune diseases

Induced bronchus-associated lymphoid tissue serves as a general priming site for T cells and is maintained by dendritic cells

Mucosal vaccination via the respiratory tract can elicit protective immunity in animal infection models, but the underlying mechanisms are still poorly understood. We show that a single intranasal application of the replication-deficient modified vaccinia virus Ankara, which is widely used as a recombinant vaccination vector, results in prominent induction of bronchus-associated lymphoid tissue (BALT). Although initial peribronchiolar infiltrations, characterized by the presence of dendritic cells (DCs) and few lymphocytes, can be found 4 d after virus application, organized lymphoid structures with segregated B and T cell zones are first observed at day 8. After intratracheal application, in vitro–differentiated, antigen-loaded DCs rapidly migrate into preformed BALT and efficiently activate antigen-specific T cells, as revealed by two-photon microscopy. Furthermore, the lung-specific depletion of DCs in mice that express the diphtheria toxin receptor under the control of the CD11c promoter interferes with BALT maintenance. Collectively, these data identify BALT as tertiary lymphoid structures supporting the efficient priming of T cell responses directed against unrelated airborne antigens while crucially requiring DCs for its sustained presence

Rapid leukocyte migration by integrin-independent flowing and squeezing

All metazoan cells carry transmembrane receptors of the integrin family, which couple the contractile force of the actomyosin cytoskeleton to the extracellular environment. In agreement with this principle, rapidly migrating leukocytes use integrin-mediated adhesion when moving over two-dimensional surfaces. As migration on two-dimensional substrates naturally overemphasizes the role of adhesion, the contribution of integrins during three-dimensional movement of leukocytes within tissues has remained controversial. We studied the interplay between adhesive, contractile and protrusive forces during interstitial leukocyte chemotaxis in vivo and in vitro. We ablated all integrin heterodimers from murine leukocytes, and show here that functional integrins do not contribute to migration in three-dimensional environments. Instead, these cells migrate by the sole force of actin-network expansion, which promotes protrusive flowing of the leading edge. Myosin II-dependent contraction is only required on passage through narrow gaps, where a squeezing contraction of the trailing edge propels the rigid nucleus

T Cell–Dendritic Cell Interaction Dynamics during the Induction of Respiratory Tolerance and Immunity

Abstract Dendritic cells (DCs) residing in the lung are known to acquire inhaled Ag and, after migration to the draining bronchial lymph node (brLN), to present it to naive T cells in an either tolerogenic or immunogenic context. To visualize endogenous lung-derived DCs, we applied fluorescent latex beads (LXs) intratracheally, thereby in vivo labeling the majority of phagocytic cells within the lung. Of note, LX-bearing cells subsequently arriving in the draining brLN were found to represent lung-derived migratory DCs. Imaging explanted brLN by two-photon laser-scanning microscopy, we quantitatively analyzed the migration and interaction behavior of naive CD4+ T cells and endogenous, lung-derived DC presenting airway-delivered Ag under inflammatory or noninflammatory conditions. Ag-specific naive CD4+ T cells engaged in stable as well as transient contacts with LX-bearing DCs in both situations and displayed similar overall motility kinetics, including a pronounced decrease in motility at 16–20 h after antigenic challenge. In contrast, the comparative analysis of T cell–DC cluster sizes as well as contact durations strongly suggests that lung-derived migratory DCs and naive CD4+ T cells form more stable, long-lasting contacts under inflammatory conditions favoring the induction of respiratory immunity.</jats:p

Afferent lymph–derived T cells and DCs use different chemokine receptor CCR7–dependent routes for entry into the lymph node and intranodal migration

International audienceBy establishing micromanipulator-guided injections into afferent lymph vessels of the popliteal lymph node (LN) in living mice, we demonstrate, using two-photon microscopy, that lymph-derived T cells entered LN parenchyma primarily from peripheral medullary sinuses while dendritic cells (DCs) transmigrated through the floor of the afferent side subcapsular sinus. Transmigrating DCs induced local changes of the subcapsular sinus floor thereby allowing the concomitant entry of T cells at these sites. Signals mediated by the chemokine receptor CCR7 were absolutely required for the directional migration of both DC and T cells into the T cell zone but were dispensable for parenchymal entry of lymph-derived T cells and dendrite probing of DC