The lymphocyte--a disgraceful gap in medical knowledge

Splenocytes and thymocytes migration patterns between lymphoid organs in pregnancy

Background

Cell migration is essential for the immune system and is frequently analyzed in adult non-pregnant animals but poorly explored in pregnant animals. However, a physiologic increased size in the spleen and periaortic lymph nodes had been reported in pregnant mice.

Methods

Using a mouse model, we transferred PKH26-stained thymocytes and splenocytes from pregnant or non-pregnant animals to receptor mice in the presence or absence of pregnancy. Percentage of PKH-26 cells and Mean Fluorescence Intensity were calculated. Non-parametric ANOVA analysis was performed.

Results

We detected that the percentage of PKH26+ thymocytes in the spleen, lymph nodes, and peripheral blood is higher in females than in males (p = 0.039). Our results showed a similar frequency of thymocytes and splenocytes from pregnant and non-pregnant mice located in receptor lymphoid organs (p > 0.05). Also, the location of marked cells was similar during the perinatal period (p > 0.05).

Conclusions

The mobility of thymocytes and splenocytes in pregnant and non-pregnant mice is similar. Therefore, we suggest that the larger size of the spleen and periaortic lymph nodes noted previously in pregnant mice could result from the retention of leukocytes in the secondary lymphoid organs.

Immunology's Coming of Age

This treatise describes the development of immunology as a scientific discipline with a focus on its foundation. Toward the end of the nineteenth century, the study of immunology was founded with the discoveries of phagocytosis by Elias Metchnikoff, as well as by Emil Behring's and Paul Ehrlich's discovery of neutralizing antibodies. These seminal studies were followed by the discoveries of bacteriolysis by complement and of opsonization by antibodies, which provided first evidence for cooperation between acquired and innate immunity. In the years that followed, light was shed on the pathogenic corollary of the immune response, describing different types of hypersensitivity. Subsequently, immunochemistry dominated the field, leading to the revelation of the chemical structure of antibodies in the 1960s. Immunobiology was preceded by transplantation biology, which laid the ground for the genetic basis of acquired immunity. With the identification of antibody producers as B lymphocytes and the discovery of T lymphocytes as regulators of acquired immunity, lymphocytes moved into the center of immunologic research. T cells were shown to be genetically restricted and to regulate different leukocyte populations, including B cells and professional phagocytes. The discovery of dendritic cells as major antigen-presenting cells and their surface expression of pattern recognition receptors revealed the mechanisms by which innate immunity instructs acquired immunity. Genetic analysis provided in-depth insights into the generation of antibody diversity by recombination, which in principle was shown to underlie diversity of the T cell receptor, as well. The invention of monoclonal antibodies not only provided ultimate proof for the unique antigen specificity of the antibody-producing plasma cell, it also paved the way for a new era of immunotherapy. Emil Behring demonstrated cure of infectious disease by serum therapy, illustrating how clinical studies can stimulate basic research. The recent discovery of checkpoint control for cancer therapy illustrates how clinical application benefits from insights into basic mechanisms. Last not least, perspectives on immunology progressed from a dichotomy between cellular-unspecific innate immunity and humoral-specific acquired immunity, toward the concept of complementary binarity.

Prostate cancer treated with brachytherapy; an exploratory study of dose-dependent biomarkers and quality of life

BACKGROUND

Low-dose-rate permanent prostate brachytherapy (PPB) is an attractive treatment option for patients with localised prostate cancer with excellent outcomes. As standard CT-based post-implant dosimetry often correlates poorly with late treatment-related toxicity, this exploratory (proof of concept) study was conducted to investigate correlations between radiation - induced DNA damage biomarker levels, and acute and late bowel, urinary, and sexual toxicity.

METHODS

Twelve patients treated with ¹²⁵I PPB monotherapy (145Gy) for prostate cancer were included in this prospective study. Post-implant CT based dosimetry assessed the minimum dose encompassing 90% (D_90%) of the whole prostate volume (global), sub-regions of the prostate (12 sectors) and the near maximum doses (D_0.1cc, D_2cc) for the rectum and bladder. Six blood samples were collected from each patient; pre-treatment, 1 h (h), 4 h, 24 h post-implant, at 4 weeks (w) and at 3 months (m). DNA double strand breaks were investigated by staining the blood samples with immunofluorescence antibodies to γH2AX and 53BP1 proteins (γH2AX/53BP1). Patient self-scored quality of life from the Expanded Prostate Cancer Index Composite (EPIC) were obtained at baseline, 1 m, 3 m, 6 m, 9 m, 1 year (y), 2y and 3y post-treatment. Spearman's correlation coefficients were used to evaluate correlations between temporal changes in γH2AX/53BP1, dose and toxicity.

RESULTS

The minimum follow up was 2 years. Population mean prostate D_90% was 144.6 ± 12.1 Gy and rectal near maximum dose D_0.1cc = 153.0 ± 30.8 Gy and D_2cc = 62.7 ± 12.1 Gy and for the bladder D_0.1cc = 123.1 ± 27.0 Gy and D_2cc = 70.9 ± 11.9 Gy. Changes in EPIC scores from baseline showed high positive correlation between acute toxicity and late toxicity for both urinary and bowel symptoms. Increased production of γH2AX/53BP1 at 24 h relative to baseline positively correlated with late bowel symptoms. Overall, no correlations were observed between dose metrics (prostate global or sector doses) and γH2AX/53BP1 foci counts.

CONCLUSIONS

Our results show that a prompt increase in γH2AX/53BP1foci at 24 h post-implant relative to baseline may be a useful measure to assess elevated risk of late RT - related toxicities for PPB patients. A subsequent investigation recruiting a larger cohort of patients is warranted to verify our findings.

Whole-body anatomy of human T cells

Knowledge of the regional tissue distribution of T cell subsets is a prerequisite for understanding protective immunity and the pathophysiology of T cell-mediated diseases. In this issue of Immunity, Sathaliyawala et al. (2012) present a comprehensive human tissue T cell analysis.

The historical milestones in the understanding of leukocyte biology initiated by Elie Metchnikoff

Progress in science is made with key discoveries, correct analyses, wrong statements, and disputes within the scientific community. Despite scientific controversies, Elie Metchnikoff has allowed the theory of phagocytes to triumph. Starting his career as a zoologist, Metchnikoff became a pathologist, beautifully defining the role of monocytes, macrophages, and neutrophils during inflammation and innate immunity. The discoveries of immune cells were made by other outstandings scientists, such as Paul Ehrlich, whose key contributions to humoral immunity led him to share the Nobel Prize with Metchnikoff. Ludwig Aschoff grouped certain cells under the term RES, according to their propensity for absorbing and storing vital stains. This classification was not always a source of accurate discoveries, and research on the exact function of RES cells led to some wanderings. This is illustrated by studies about the nature of the antibody-producing cells, which were first thought to belong to the RES, before being identified as plasmocytes and lymphocytes.

T-cell homing to the gut mucosa: general concepts and methodological considerations

Effector/memory T cells can migrate to most extra-lymphoid tissues in the body. However, migration to the intestinal mucosa requires the expression of very specific homing receptors on T cells, integrin α4β7 and chemokine receptor CCR9. These receptors are induced by all-trans retinoic acid (RA), a vitamin A metabolite that is specifically synthesized by gut-associated dendritic cells (DC), but not by extra-intestinal DC. Here we summarize some general concepts on T cell homing with an emphasis on the gut mucosa. We also discuss experimental strategies to generate gut-homing T cells in vivo and in vitro and the techniques to track gut-homing T cells.

The lymph node revisited: development, morphology, functioning, and role in triggering primary immune responses

Scenarios have been proposed to explain how lymphoid components of a lymph node favor the encounter of a drained antigen with a circulating competent naïve lymphocyte to trigger a primary immune response. However, these scenarios rest on incorrect concepts about the organ. This situation resulted from a loss of interest for studies on in vivo lymphoid organs due to a widespread switch, decades ago, to work on suspended lymphoid cells. However, an in vivo holistic study of the organ continued in our laboratory. The present review synthesizes resulting knowledge on lymph node morphology and global functioning. We show that the opening of an afferent lymphatic vessel into the subcapsular sinus is the focal point from which the related portion of a lymph node-a node compartment-is developed. As to the formation of a compartment's lymphoid components, it is neonatally orchestrated by the dichotomic nature and distribution of antigens in this subcapsular sinus, which determines a dichotomic recruitment of circulating cells and the compartment's architectural complexity. The transport process of an antigen from a given tissue territory into restricted sites of the draining compartment further defines its local morphological features and activities, while providing the possibility to reduce the wandering of a short-lived naïve cell through innumerable target-devoid sites. We also explain that the nodal lymphoid components are not implicated in the triggering of primary responses, but are rather products of such responses. Scenarios for the triggering of primary responses, consistent with real node morphology and functioning, are proposed.

The immune system and cancer

Cancer patients mount adaptive immune responses against their tumor. However, while tumor-infiltrating lymphocytes and natural-killer (NK) cells try to detect and eliminate malignant cells, they eventually fail when these malignant cells develop mechanisms to evade effective immunosurveillance. First, malignant cells produce immunosuppressive cytokines and prostaglandins that skew the immune response toward a Th2 response, resulting in a humoral response with significantly less antitumor capacities, generating a low interleukin-2 environment blocking NK cell division, T-helper cell proliferation, and T-cytotoxic cell proliferation and function. Second, immunoresistant malignant cell variants emerge through selection of major histocompatibility class I and II and antigen-processing mutants reducing antigenicity. Finally, malignant cells may actively eliminate T-cells via activation-induced cell death or by mounting a counterattack through Fas ligand expression.

Monitoring cellular movement in vivo with photoconvertible fluorescence protein "Kaede" transgenic mice

Kaede is a photoconvertible fluorescence protein that changes from green to red upon exposure to violet light. The photoconversion of intracellular Kaede has no effect on cellular function. Using transgenic mice expressing the Kaede protein, we demonstrated that movement of cells with the photoconverted Kaede protein could be monitored from lymphoid organs to other tissues as well as from skin to the draining lymph node. Analysis of the kinetics of cellular movement revealed that each subset of cells in the lymph node, such as CD4(+) T, CD8(+) T, B, and dendritic cells, has a distinct migration pattern in vivo. Thus, the Kaede transgenic mouse system would be an ideal tool to monitor precise cellular movement in vivo at different stages of immune response to pathogens as well as in autoimmune diseases.

Finding a way out: lymphocyte egress from lymphoid organs

The egress of lymphocytes from the thymus and secondary lymphoid organs into circulatory fluids is essential for normal immune function. The discovery that a small-molecule inhibitor of lymphocyte exit, FTY720, is a ligand for sphingosine 1-phosphate (S1P) receptors led to studies demonstrating that S1P receptor type 1 (S1P1) is needed in T cells and B cells for their egress from lymphoid organs. S1P exists in higher concentrations in blood and lymph than in lymphoid organs, and this differential is also required for lymphocyte exit. Transcriptional and post-translational mechanisms regulate S1P1 and thus the egress of lymphocytes. In this review we discuss the body of evidence supporting a model in which lymphocyte egress is promoted by encounter with S1P at exit sites. We relate this model to work examining the effects of S1P receptor agonists on endothelium.

A brief history of CD8 T cells

CD8 T cells comprise a powerful branch of the adaptive immune system, yet were not formally recognized until long after the discovery of antibody. CD8 T cells contribute to the eradication of intracellular infections and to the control of many chronic infections. There is tempered optimism that CD8 T cell memory elicited via vaccination may hold the key to manufacturing protective immunity against pathogens that cause chronic infections in humans. The specificity and destructive capabilities of CD8 T cells may also be harnessed for the eradication of tumors. However, CD8 T cells also contribute to a variety of clinical difficulties such as immune mediated pathology, rejection of organ transplants, and autoimmunity. Clearly, learning how to safely generate protective long-lived CD8 T cell memory and how to control or eliminate specific unwanted responses could deliver substantial clinical rewards, and there is a great need for continued research on the biology and therapeutic potential of these cells. Herein, we recount the historical developments leading to the discovery of CD8 T cells, highlight a few of the important discoveries that have followed, and discuss some of the critical issues on the horizon.

Molecular Determinants Controlling Homeostatic Recirculation and Tissue-Specific Trafficking of Lymphocytes

The homeostasis of the immune system is maintained by the recirculation of naïve lymphocytes through the secondary lymphoid tissues, such as the lymph nodes, Peyer's patches, and spleen. Upon insult by pathogens or antigens, lymphocytes become activated, and the regulated trafficking of these cells results in the integration of systemic and regional immune responses. The exquisite specificity of such lymphocyte trafficking is determined by tissue-specific guidance signals expressed by the endothelial cells of postcapillary venules, combined with counterreceptors expressed by the circulating lymphocytes. The high endothelial venules can selectively guide naïve lymphocytes into the lymph nodes and Peyer's patches by expressing a unique combination of vascular addressins, lymphocyte-specific chemokines, and chemokine-binding molecules. The inflamed postcapillary venules in extralymphoid tissues, such as the skin and intestinal lamina propria, also use a distinct array of endothelial adhesion molecules and tissue- selective chemokines, and support the recruitment of effector and memory lymphocytes that express the appropriate receptors for tissue-specific trafficking. In this review, we summarize the present understanding of the homeostatic recirculation of naïve lymphocytes through the secondary lymphoid tissues and the specific targeting of antigen-experienced lymphocytes into the effector sites. We also revisit some previous studies that reported apparently conflicting observations.

Egress: a receptor-regulated step in lymphocyte trafficking

Blood lymphocyte numbers, which are maintained by recirculation through secondary lymphoid organs, are essential for the efficient development of immune responses. Recirculating populations of B and T lymphocytes are regulated by the sphingosine-1-phosphate (S1P) receptor-dependent control of lymphocyte egress. T-cell egress from thymus into blood, egress from lymph node and Peyer's patch into lymph, and B-cell egress into lymph are rapidly and completely inhibited by agonism of S1P receptors. Mesenteric lymph nodes show log-jamming of lymphocytes subjacent to sinus-lining endothelium. Agonism of S1P receptors produces rapid peripheral blood lymphopenia, which is maintained in the presence of receptor agonist. Effector CD4+ and CD8+ T cells, produced by clonal expansion in draining lymph node in response to antigen, are sequestered in lymph node and fail to reach the peripheral blood. The S1P receptor system may represent an early physiological link between the non-specific inflammatory response and the alteration of lymphocyte traffic through draining lymph nodes. Pharmacological subversion of the S1P receptor system, through systemic S1P agonist-induced inhibition of lymphocyte egress, suppresses antigenic responses to peripheral, but not to systemically, delivered antigen. This inhibition induces significant immunosuppression in models of transplantation and autoimmune tissue damage that may prove to be of clinical benefit.

Autonomous T cell trafficking examined in vivo with intravital two-photon microscopy

The recirculation of T cells between the blood and secondary lymphoid organs requires that T cells are motile and sensitive to tissue-specific signals. T cell motility has been studied in vitro, but the migratory behavior of individual T cells in vivo has remained enigmatic. Here, using intravital two-photon laser microscopy, we imaged the locomotion and trafficking of naive CD4(+) T cells in the inguinal lymph nodes of anesthetized mice. Intravital recordings deep within the lymph node showed T cells flowing rapidly in the microvasculature and captured individual homing events. Within the diffuse cortex, T cells displayed robust motility with an average velocity of approximately 11 microm x min(-1). T cells cycled between states of low and high motility roughly every 2 min, achieving peak velocities >25 microm x min(-1). An analysis of T cell migration in 3D space revealed a default trafficking program analogous to a random walk. Our results show that naive T cells do not migrate collectively, as they might under the direction of pervasive chemokine gradients. Instead, they appear to migrate as autonomous agents, each cell taking an independent trafficking path. Our results call into question the role of chemokine gradients for basal T cell trafficking within T cell areas and suggest that antigen detection may result from a stochastic process through which a random walk facilitates contact with antigen-presenting dendritic cells.

Alteration of lymphocyte trafficking by sphingosine-1-phosphate receptor agonists

Blood lymphocyte numbers, essential for the development of efficient immune responses, are maintained by recirculation through secondary lymphoid organs. We show that lymphocyte trafficking is altered by the lysophospholipid sphingosine-1-phosphate (S1P) and by a phosphoryl metabolite of the immunosuppressive agent FTY720. Both species were high-affinity agonists of at least four of the five S1P receptors. These agonists produce lymphopenia in blood and thoracic duct lymph by sequestration of lymphocytes in lymph nodes, but not spleen. S1P receptor agonists induced emptying of lymphoid sinuses by retention of lymphocytes on the abluminal side of sinus-lining endothelium and inhibition of egress into lymph. Inhibition of lymphocyte recirculation by activation of S1P receptors may result in therapeutically useful immunosuppression.

The Relationship of Blood Lymphocytes to the Recirculating Lymphocyte Pool

Lymphocyte recirculation facilitates the detection and elimination of pathogens and the dissemination of immunologic memory. It is generally assumed that all small lymphocytes in the blood are actively recirculating, yet there is little quantitative data directly comparing the migration of this population with actively recirculating, lymph-derived lymphocytes. In this study blood lymphocytes were labeled with fluorescein isothiocyanate (FITC), and lymph lymphocytes were labeled with CM-DiI, reinfused intravenously, and monitored in blood and lymph. After equilibration the concentration of blood lymphocytes was several times higher in blood than in lymph, whereas lymph lymphocytes displayed the opposite behavior. This suggested that blood lymphocytes did not recirculate as efficiently as lymph lymphocytes, so we examined the following blood lymphocyte subsets in greater detail: B cells, CD4+, CD8+, and γδ T cells. Within 4 hours postinjection the percentage of FITC+CD8+ and CD4+ lymphocytes fell in the blood and remained significantly lower than the injected sample. In contrast, the concentration of FITC+ γδ T cells did not change, and the percentage of FITC+ B cells increased. These data suggest that subpopulations of B and perhaps γδ T lymphocytes in the blood do not recirculate efficiently through lymph nodes.

The Relationship of Blood Lymphocytes to the Recirculating Lymphocyte Pool

Lymphocyte recirculation facilitates the detection and elimination of pathogens and the dissemination of immunologic memory. It is generally assumed that all small lymphocytes in the blood are actively recirculating, yet there is little quantitative data directly comparing the migration of this population with actively recirculating, lymph-derived lymphocytes. In this study blood lymphocytes were labeled with fluorescein isothiocyanate (FITC), and lymph lymphocytes were labeled with CM-DiI, reinfused intravenously, and monitored in blood and lymph. After equilibration the concentration of blood lymphocytes was several times higher in blood than in lymph, whereas lymph lymphocytes displayed the opposite behavior. This suggested that blood lymphocytes did not recirculate as efficiently as lymph lymphocytes, so we examined the following blood lymphocyte subsets in greater detail: B cells, CD4+, CD8+, and γδ T cells. Within 4 hours postinjection the percentage of FITC+CD8+ and CD4+ lymphocytes fell in the blood and remained significantly lower than the injected sample. In contrast, the concentration of FITC+ γδ T cells did not change, and the percentage of FITC+ B cells increased. These data suggest that subpopulations of B and perhaps γδ T lymphocytes in the blood do not recirculate efficiently through lymph nodes.