The effect of antigen on the output of recirculating T and B lymphocytes from single lymph nodes

In Sickness and in Health: The Immunological Roles of the Lymphatic System

The lymphatic system plays crucial roles in immunity far beyond those of simply providing conduits for leukocytes and antigens in lymph fluid. Endothelial cells within this vasculature are distinct and highly specialized to perform roles based upon their location. Afferent lymphatic capillaries have unique intercellular junctions for efficient uptake of fluid and macromolecules, while expressing chemotactic and adhesion molecules that permit selective trafficking of specific immune cell subsets. Moreover, in response to events within peripheral tissue such as inflammation or infection, soluble factors from lymphatic endothelial cells exert “remote control” to modulate leukocyte migration across high endothelial venules from the blood to lymph nodes draining the tissue. These immune hubs are highly organized and perfectly arrayed to survey antigens from peripheral tissue while optimizing encounters between antigen-presenting cells and cognate lymphocytes. Furthermore, subsets of lymphatic endothelial cells exhibit differences in gene expression relating to specific functions and locality within the lymph node, facilitating both innate and acquired immune responses through antigen presentation, lymph node remodeling and regulation of leukocyte entry and exit. This review details the immune cell subsets in afferent and efferent lymph, and explores the mechanisms by which endothelial cells of the lymphatic system regulate such trafficking, for immune surveillance and tolerance during steady-state conditions, and in response to infection, acute and chronic inflammation, and subsequent resolution.

T Cell Trafficking through Lymphatic Vessels

T cell migration within and between peripheral tissues and secondary lymphoid organs is essential for proper functioning of adaptive immunity. While active T cell migration within a tissue is fairly slow, blood vessels and lymphatic vessels (LVs) serve as speedy highways that enable T cells to travel rapidly over long distances. The molecular and cellular mechanisms of T cell migration out of blood vessels have been intensively studied over the past 30 years. By contrast, less is known about T cell trafficking through the lymphatic vasculature. This migratory process occurs in one manner within lymph nodes (LNs), where recirculating T cells continuously exit into efferent lymphatics to return to the blood circulation. In another manner, T cell trafficking through lymphatics also occurs in peripheral tissues, where T cells exit the tissue by means of afferent lymphatics, to migrate to draining LNs and back into blood. In this review, we highlight how the anatomy of the lymphatic vasculature supports T cell trafficking and review current knowledge regarding the molecular and cellular requirements of T cell migration through LVs. Finally, we summarize and discuss recent insights regarding the presumed relevance of T cell trafficking through afferent lymphatics.

Antibody and cytokine responses in efferent lymph following vaccination with different adjuvants

The cannulated efferent lymph node in sheep was used to examine the effect of different adjuvants on the antibody and cytokine responses following sub-cutaneous vaccination with a recombinant Taenia ovis antigen (45 W). Vaccination with Quil A elicited relatively higher levels of IgM than did IFA or Al(OH)3. In general, 45 W specific IgG1 and IgG2 titres were higher and maintained for longer periods of time in lymph from sheep vaccinated with IFA and lower and shorter lived in animals which received the Al(OH)3 based vaccine. Interferon-gamma was present within one day in efferent lymph from all sheep which received the Quil A formulation and in only one of the three sheep that received the IFA formulation. GM-CSF was only detected in lymph from sheep vaccinated with the IFA formulation. IL-8 was present in lymph prior to vaccination and only animals which received the Quil A formulation had increased levels of IL-8 after vaccination. Neither of the inflammatory cytokines IL-1 beta and TNF alpha were detected in efferent lymph from any animals in this study. This paper highlights the potential of the lymphatic cannulation model for investigations of the in vivo action of adjuvants.

Increased IgA-producing cells in the blood of patients with active Henoch-Schönlein purpura

Peripheral blood lymphocytes (PBL) producing IgA, IgM, and IgG, both spontaneously and after pokeweed mitogen stimulation in cell culture, were determined by a protein A hemolytic plaque assay in 20 children with active Henoch-Schönlein purpura (HSP), 42 with inactive disease, 22 normal controls of the same ages, and 18 children with upper respiratory tract infections (URTI). The geometric mean of circulating IgA-producing cells in active HSP (1,016 X divided by 1.55 cells/10(6) PBL) was increased when compared with the group with inactive disease (P less than 0.001), normal controls (P less than 0.001), and children with URTI (542 X divided by 2.03 cells/10(6) PBL, P less than 0.05). The number of circulating IgM-producing cells was slightly increased in active HSP (260 X divided by 2.65 cells/10(6) PBL) and URTI (256 X divided by 3.16 cells/10(6) PBL). Both values were higher than those found in the group with inactive disease (113 X divided by 2.26 cells/10(6) PBL, P less than 0.01). There were no significant differences among the 4 groups in the number of circulating IgG-producing cells. The number of cells producing each type of immunoglobulin after in vitro stimulation with pokeweed mitogen was similar in patients with active HSP, normal controls, and the group with inactive disease. These data demonstrate a selective increase in the number of circulating IgA-producing cells only during disease activity, and add further support to a possible pathogenic role of this immunoglobulin in HSP.