Lymphocyte traffic through lymph nodes during cell shutdown

Power Doppler ultrasonographic assessment of the joint-draining lymph node complex in rheumatoid arthritis: a prospective, proof-of-concept study on treatment with tumor necrosis factor inhibitors

BACKGROUND

Emerging research on the mechanisms of disease chronicity in experimental arthritis has included a new focus on the draining lymph node (LN). Here, we combined clinical-serological analyses and power Doppler ultrasound (PDUS) imaging to delineate noninvasively the reciprocal relationship in vivo between the joint and the draining LN in patients with rheumatoid arthritis (RA).

METHODS

Forty consecutive patients refractory to conventional synthetic disease-modifying anti-rheumatic drugs were examined through parallel PDUS of the hand-wrist joints and axillary LNs and compared with 20 healthy subjects. A semiquantitative score for LN gray-scale (GS) parameters (nodal hypertrophy and cortical structure) and LN PD signal was developed. A 6-month follow-up study with serial sonographic assessments was then performed on initiation of tumor necrosis factor (TNF) inhibitors.

RESULTS

PDUS analysis of RA axillary LNs revealed the existence of marked inter-individual heterogeneity and of quantitative differences compared with healthy individuals in both GS and PD characteristics. RA LN changes were plastic, responsive to anti-TNF treatment, and displayed a degree of concordance with synovitis activity in peripheral joints. However, low LN PD signal at baseline despite active arthritis was strongly associated with a poor clinical response to TNF blockade.

CONCLUSIONS

PDUS analysis of the draining LN in RA allows capture of measurable inter-individual differences and dynamic changes linked to the underlying pathologic process. LN and joint sonographic assessments are nonredundant approaches that may provide independent perspectives on peripheral disease and its evolution over time.

The draining lymph node in rheumatoid arthritis: current concepts and research perspectives

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease of unknown aetiology, leading to progressive damage of bone and cartilage with functional impairment and disability. Whilst the synovial membrane represents the epicentre of the immune-inflammatory process, there is growing evidence indicating the potential involvement of additional anatomical compartments, such as the lung, bone marrow, and secondary lymphoid tissues. Draining lymph nodes represent the elective site for tissue immune-surveillance, for the generation of adaptive immune responses and a candidate compartment for the maintenance of peripheral tolerance. Despite the precise role of the juxta- and extra-articular lymph node stations in the pathogenesis of RA remaining poorly defined, several lines of research exploiting new technological approaches are now focusing on their assessment as a potential new source of pathobiologic information, biomarkers, and complementary therapeutic targets. In this review we present an updated overview of the main concepts driving lymph node research in RA, highlighting the most relevant findings, current hypothesis, and translational perspectives.

High endothelial venules as traffic control points maintaining lymphocyte population homeostasis in lymph nodes

Millions of lymphocytes enter and exit mammal lymph nodes (LNs) each day, accessing the parenchyma via high endothelial venules (HEVs) and egressing via lymphatics. Despite this high rate of cellular flux and the many entry and exit sites within a given LN, the number of lymphocytes present in a resting LN is extraordinary stable over time, raising the question of how this steady-state is maintained. Here we have examined the anatomic details of lymphocyte movement in HEVs, finding that HEVs create pockets within which lymphocytes reside for several minutes before entering the LN proper. The function of these pockets was revealed in experiments performed under conditions in which lymphocyte egress from the LN was compromised by any of several approaches. Under such conditions, the HEVs pockets behaved as "waiting areas" in which lymphocytes were held until space was made available to them for entry into the parenchyma. Thus, rather than being simple entry ports, HEVs act as gatekeepers able to stack, hold and grant lymphocytes access to LN parenchyma in proportion to the rate of lymphocyte egress from the LN, enabling the LN to maintain a constant steady-state cellularity while supporting the extensive cellular trafficking necessary for repertoire scanning.

Memory T-cell trafficking: new directions for busy commuters

The immune system is unique in representing a network of interacting cells of enormous complexity and yet being based on single cells travelling around the body. The development of effective and regulated immunity relies upon co-ordinated migration of each cellular component, which is regulated by diverse signals provided by the tissue. Co-ordinated migration is particularly relevant to the recirculation of primed T cells, which, while performing continuous immune surveillance, need to promptly localize to antigenic sites, reside for a time sufficient to carry out their effector function and then efficiently leave the tissue to avoid bystander damage. Recent advances that have helped to clarify a number of key molecular mechanisms underlying the complexity and efficiency of memory T-cell trafficking, including antigen-dependent T-cell trafficking, the regulation of T-cell motility by costimulatory molecules, T-cell migration out of target tissue and fugetaxis, are reviewed in this article.

The recirculation of T and B lymphocytes in the athymic, nude rat

The recirculation of lymphocytes through the tissues and their return to the blood were compared in nude and euthymic rats. Three approaches were used: the organ distribution of 15Cr-labelled lymphocytes from nude or euthymic donors at 24 h after injection; the compartmental distribution of B and T lymphocytes as assessed by autoradiography of the spleen, lymph nodes, and Peyer's patches; and the tempo of recirculation from blood to thoracic duct lymph as estimated by counting timed fractions of lymph from a recipient of labelled lymphocytes. The following conclusions were drawn: (1) The distribution of lymphocytes between organs and within organs is very similar in nude and euthymic recipients. In particular, B lymphocytes proceed normally to the follicular areas in the absence of T cells. (2) The recirculation from blood to lymph is delayed in nude rats. (3) For equal numbers of B and T cells injected intravenously about half as many B cells as T cells enter mesenteric and cervical lymph nodes, but approximately equal numbers of B and T cells enter the spleen and Peyer's patches.

Specific selection of antigen-reactive lymphocytes into antigenically stimulated lymph nodes in sheep

Sheep were primed to a variety of antigens and the efferent lymphatic from a popliteal lymph node was cannulated. The cannulated node was challenged repeatedly with PPD and all the lymph and cells removed from the animal. During this time the PBL were monitored for reactivity to all antigens (purified protein derivative of tuberculin [PPD], johnin, and keyhole limpet hemocyanin [KLH]) by the vitro transformation assay. The response of these cells to PPD was found to be gradually eliminated after repeated challenge of the cannulated node with that antigen. The response to the other antigens was unimpaired. No depletion of this response to PPD occurred in cannulated sheep when the antigen was given into a noncannulated node. In vivo delayed-type hypersensitivity skin test and helper T cell assays confirmed that there is a specific selection of antigen-reactive cells from the recirculating lymphocyte pool into antigen-stimulated lymph nodes.