Development of T and B cell areas in peripheral lymphoid organs of the rat

In the present study the early development of peripheral lymphoid organs (spleen, popliteal lymph node, mesenteric lymph node and Peyer's patches) is described in terms of homing patterns of T and B cells, demonstrated with immunohistoperoxidatic detection of characteristic membrane antigen in normal rats and with routine histology in neonatally thymectomized rats. In the first days after birth the peripheral lymphoid organs are almost exclusively populated by T cells. After neonatal thymectomy lymphocytes appear in the dome areas of Peyer's patches from four to six days after birth, in mesenteric and popliteal lymph nodes lymphocytes are found in the outer cortex from day 6 and day 8 respectively and in the marginal zone of the spleen from eight days onwards. These lymphocytes showed no membrane staining when reacted for T antigen with immunohistoperoxidatic techniques. The morphological evidence for considering Peyer's patches of rats as central inductive sites for the generation of B cells is poor. The discrepancy in the order of appearance of T and B cell (sub)populations in spleen compartments in normal ontogenetic development and lethally irradiated, stem cell reconstituted animals is discussed.     

Selective effect on T and B cell subpopulations in rat lymphoid organs after urethan treatment.

In vitro phytohemagglutinin (PHA) and concanavalin A (Con A) responsiveness of thymus and bone marrow cells, and E, EA, and EAC rosette-forming cells (E, EA, EAC) of these organs and spleen were studied in Fisher rats at various time intervals following a carcinogenic treatment with urethan (UR). Immediately after treatment, organ cellularities were drastically reduced with a progressive recovery as time passed. 1 day after treatment, the response of thymocytes to PHA showed a fourfold increase while organ cellularity dropped to 1%. This response fell below normal values after 7 days with an overshoot after days 14 and 21. UR-treated bone marrow cells showed a response to PHA below normal values after 1 and 7 days, a twofold increase after 3 days and an overshoot after 14 and 21 days. The responsiveness to Con A of both organs was affected by UR treatment to a much lesser extent, although following a pattern similar to that of PHA. E were never found, whether in normal nor in UR-treated animals. As far as the B-cell compartment is concerned, UR causes a progressive diminution of EAC, while the number of EA remains unaffected. The data are discussed in terms of selective effect on T- and B-cell subpopulations.     

Comparative histologic, histochemical, and histomorphometric studies of T and B cell areas in peripheral lymphoid organs of normal young adult BALB/C mice.

T cell areas can be distinguished from adjacent B cell compartments in routinely stained histologic sections of paraffin-embedded mouse lymph nodes and spleens by their comparatively loose texture. The reliability of this morphologic criterion for identifying T cell areas has been proven in comparative histologic, enzyme-histochemical, and immunohistochemical investigations. It is thus possible to determine the size of functionally different compartments in the lymph nodes and spleen of the mouse with sufficient accuracy by the use of conventional histologic techniques. According to our subsequent histomorphometrical studies in two groups of inbred mice matched with respect to age and strain, the proportions of B cell areas in the peripheral lymphoid organs varied significantly depending on environmental conditions, whereas the proportions of T cell areas were stable.     

Quantification of BCG-induced reactions of T and B areas in peripheral lymphoid organs of young adult BALB/c mice. A histomorphometrical and autoradiographical study.

Significant structural alterations of the axillary lymph nodes and spleens were revealed by histomorphometry following intraperitoneal injection of BCG into young adult BALB/c mice. The relative proportions of the germinal center areas were increased in lymph nodes as well as in spleens. The overall proportion of the B cell areas, however, showed a significant increase only in the spleens, compared to a significant reduction in the lymph nodes. By contrast, T cell areas appeared significantly reduced in the spleens, while their size was almost doubled in the lymph nodes. The labeling index in the lymph node paracortical areas was also doubled autoradiographically. The structural changes in the lymph nodes and spleens differed not only in quality, but also in their time course. In lymph nodes, the altered proportions of the T and B cell areas persisted from the second through the sixth week after BCG treatment. By contrast, structural changes in the spleen began to subside 2 weeks after treatment, and after 6 weeks the proportions of the T and B cell areas in the spleen had returned to normal. These quantitative morphologic findings suggest a difference in the functional roles of lymph nodes and spleen in the systemic immune response to BCG.     

The proportions of B and T lymphocytes in lymphomas, peripheral nerves and lymphoid organs in Marek's disease

The proportions of cells bearing B cell, T cell and immunoglobulin (Ig), cell membrane markers have been studied in chickens with Marek's disease (MD). The proportions of B, T and Ig-bearing cells were similar in lymphomas arising in various organs and in infiltrated nerves, irrespective of type of nerve lesion. T cells provided the major component, and B and Ig cells the minor components, of the lymphoid cell populations. Compared with the corresponding organ from uninfected control chickens, bursa and spleen from MD-affected birds showed increases in the proportions of T cells and decreases of B and Ig cells. In the bursa, and probably in the spleen, the increase in the proportion of T cells was caused by lymphomatous infiltration. In the thymus of MD-affected chickens the proportion of T cells was decreased, and of B cells increased.     

Electrophoresis of lymphoid cells. Characterization of human B and T cells in peripheral lymphoid tissues

Small lymphocytes from human blood, tonsils, spleen and lymph nodes showed a bimodal distribution on electrophoresis, the electrophoretic mobility (EPM) of one group being slow, the other fast. The difference in mean EPM between the slow and fast groups was about 30%. The percentage of slow cells in each organ was similar to that of cells with surface-bound immunoglobulin as judged by immunofluorescence studies. It was therefore concluded that a major proportion of B cells has a relatively low net surface charge while that of the T cells is higher.     

Ultrastructural study of germinal center macrophages in peripheral lymphoid organs of the rat

The ultrastructural study of macrophages of germinal centers in the secondary lymphoid follicles of the rat spleen and mesenteric lymph nodes was performed. It was demonstrated that besides macrophages containing necrotic lymphocytes and plasma cells in various stages of degradation (which are already well described in the literature) the germinal centers are also populated with macrophages displaying specific ultrastructural features which enable their precise identification. These cells contain numerous vacuolar inclusions of different size, filled with electron lucent, flocculent material. The dense bodies and membrane profiles are also present in varying amount within the vacuolar content. The dense bodies contain polysaccharides which are detected by the thiocarbohydrazide-silver proteinate method. Very rarely, these cells contain the phagocytosed cellular debris, which is readily distinguished from the cytoplasmic inclusions.     

Dendritic cells in the T-cell areas of lymphoid organs

Summary: Substantial numbers of dendritic cells (DCs) are found in the T-cell areas of peripheral lymphoid organs such as the spleen, lymph node and Peyer's patch. By electron microscopy these DCs (also called interdigitating cells) form a network through which T cells continually recirculate. The cytological features of DCs in the T-cell areas, as well as a number of markers detected with monoclonal antibodies, are similar to mature DCs that develop from other sites such as skin and bone marrow. Some markers that are expressed in abundance are: MHC II and the associated invariant chain, accessory molecules such as CD40 and CD86, a multilectin receptor for antigen presentation called DEC-205, the integrin CD11c, several antigens within the endocytic system that are detected by monoclonal anti-bodies but are as yet uncharacterized at the molecular level, and, in the human system, molecules termed Sl00b, CD83 and p55. DCs in the periphery can pick up antigens and migrate to the T-cell areas to initiate immunity However, there are new observations that DCs within the T-cell areas also express high levels of self-antigens and functional fas-ligand capable of Inducing CD4⁺ T-cell death. We speculate that there are at least 2 sets of DCs in the T-cell areas, a migratory myeloid pathway that brings in antigens from the periphery and induces immunity, and a more resident lymphoid pathway that presents self-antigens and maintains tolerance.     

Development of cytoplasmic CD3+/T cell receptor-negative cells in the peripheral lymphoid tissues of chickens.

In a study of T cell ontogeny using monoclonal antibodies specific for chicken T cell receptors (TcR) and associated cell surface molecules, we found a subset of lymphocytes that express cytoplasmic CD3 epitopes in the absence of cell surface CD3/TcR complexes. Approximately half of these cells, which were present in the spleen, bursa and intestine of young chick embryos, expressed surface CD8. None expressed CD4, TcR 1 (gamma/delta), TcR 2 (alpha/beta) or TcR 3 (a third CD3-associated heterodimer in the chicken). These cytoplasmic CD3+CD8 +/- cells, tentatively named TcR 0 cells to denote their lack of surface TcR, appeared first in the spleen of 8-day embryos, 4 days before TcR expression begins in the thymus, and reached a peak frequency of approximately 10% of the splenic cell in 14-day embryos. The TcR 0 cells were also present in adult birds, where they comprised only about 1% of the CD3+ spleen cells and approximately 40% of the lymphocytes in the intestinal epithelium. We conclude that the avian TcR 0 cells represent a thymus-independent lineage of lymphocytes which, like natural killer cells in mammals, may play an important role in body defense.     

Development of peripheral B and T lymphocytes in piglets.

The percentage of B and T lymphocytes in the peripheral blood of piglets during their first 35 days of life was estimated by means of the immunofluorescence-labelled anti-L chains sera and the spontaneous E-rosette techniques. The mean values obtained for adult pigs PBL were 23.8 +/- 10.2% of B and 38.0 +/- 8.4% of T lymphocytes. The piglets showed a linear increase for the B lymphocytes starting from a mean value of 4% observed for the newborns. The trend of the T lymphocytes was represented by a bimodal curve. It starts for newborns at 3% and shows a change in shape by the 10th day. It is suggested that the piglets have adult levels of B and T lymphocytes by the time of weaning.     

Quantification of B, T and null lymphocyte subpopulations in the blood and lymphoid organs of the pig.

Research on the pig's immune system is not only of general biological interest; the pig is also becoming more important as a large animal model in human biomedical research, e.g. as a donor for xeno-transplantation. With the increasing panel of monoclonal antibodies against porcine lymphocyte markers it is possible to gain more insight into the distribution and phenotype of lymphocyte subpopulations in the pig. In this study we investigated B cells (surface IgG: sIgG, sIgM and sIgA) and T cells (CD2, CD4, CD8, 8/1, MAC320) in the peripheral blood (pBL), thymus, spleen, tonsil, mesenteric and inguinal lymph nodes (mLN, iLN), jejunal and ileal Peyer's patches (jejPP, ilPP) in G?ttingen minipigs. A flow cytometric technique was employed which enabled three color indirect immunofluorescence. B cell stained for surface IgG and surface IgA were found only in small percentages. Surface IgM positive cells were distributed at higher rates, with up to 24.9% in the iLN. Up to 64.2% of CD4+ and up to 73.1% of CD8+ cells were observed in the thymus. Most of the CD4+ cells were CD4/CD8 double positive cells. These cells were mostly triple positive in combination with CD2. A larger fraction of CD2- were CD8- which are taken to be NK cells. MAC320, a marker for a subtype of gamma/delta T cells, was predominantly found on cells in the pBL. The standardized flow cytometric technique produced comparable data on the distribution of major lymphocyte subpopulations in the blood and different lymphoid organs of the pig. The results provide a basis for future studies using the pig as animal model.     

Chemokine-mediated control of T cell traffic in lymphoid and peripheral tissues

Antigen-driven T cell education and subsequent pathogen elimination present particular challenges for the immune system. Pathogens generally enter the body at peripheral sites such as the skin, gastrointestinal tract or lung, areas from which na?ve T cells are largely excluded. Instead, na?ve T cells constantly recirculate through secondary lymphoid organs, such as lymph nodes and Peyer's patches, in search for antigen brought to these locations by means of afferent lymphatic channels. Here, antigen-loaded dendritic cells present antigen-peptide-MHC complexes to clonotypic T cells and provide appropriate co-stimulatory signals for immune response initiation. As a result, short-lived effector T cells and long-lived memory T cells are generated that reach the peripheral tissue for participation in immune responses and immune surveillance. Effector and memory T cell relocation is non-random, due to tissue-specific "address codes" that allow proper tissue homing. This process involves adhesion molecules, including selectins, integrins, and corresponding vascular ligands as well as the large family of chemokines and their receptors. Here, we discuss the changes in chemokine receptor expression that occur during T cell activation and differentiation, and the ways in which these changes impact on the migration potential of na?ve, effector, and memory T cells. We summarize our current understanding of T cell homing to the T zone and B cell follicles within secondary lymphoid tissues and highlight the two chemokine receptors CCR7 and CXCR5 that recognize chemokines constitutively present either in the T zone (CCR7 ligands CCL19/ELC and CCL21/SLC) or follicular compartment (CXCR5 ligand CXCL13/BCA-1). CCR7 is characteristic for naive and central memory T (T(CM)) cells whereas CXCR5 distinguishes follicular B helper T (T(FH)) cells. In addition, we further subdivide long-lived memory T cells into CCR7-negative effector memory T (T(EM)) cells and peripheral immune surveillance T (T(PS)) cells. The latter term designates the extraordinarily large subset of memory T cells with primary residence in normal (healthy) peripheral tissues. Our current understanding of T(PS) cell migration and function is highly fragmentary, but these cells are thought to provide immediate protection locally at the site of pathogen entry. Here, we propose that the tissue distribution of T(PS) cells is determined by a distinct set of chemokines and corresponding receptors that differs from those operating in secondary lymphoid tissues and inflammatory sites.     

The heterogeneity of the reticulum of rat peripheral lymphoid organs identified by monoclonal antibodies

We have developed a panel of six monoclonal antibodies, ED10-ED15, directed against reticular cells in peripheral lymphoid organs. Immunohistochemistry revealed prominent differences between these antibodies with regard to their tissue distribution in lymphoid and non-lymphoid organs. Furthermore, the determinants recognized by ED10-ED13 were found to be differentially expressed by reticular cells occupying the various specialized compartments present in peripheral lymphoid organs. The reactivity patterns of these antibodies observed during the ontogenetic development of the spleen suggest that they recognize differentiation antigens expressed by reticular cells. In contrast, ED14 and ED15 were found to have a relatively ubiquitous tissue distribution recognizing reticular cells in each compartment, with a constitutive reactivity during splenic ontogeny. The present results indicate that reticular cells form a heterogeneous population within the lymphoid organs.     

T cell help to B cells: Cognate and atypical interactions in peripheral and intestinal lymphoid tissues

Enduring immunity against harmful pathogens depends on the generation of immunological memory. Serum immunoglobulins are constantly secreted by long-lived antibody-producing cells, which provide extended protection from recurrent exposures. These cells originate mainly from germinal center structures, wherein B cells introduce mutations to their immunoglobulin genes followed by affinity-based selection. Generation of high-affinity antibodies relies on physical contacts between T and B cells, a process that facilitates the delivery of fate decision signals. T-B cellular engagements are mediated through interactions between the T cell receptor and its cognate peptide presented on B cell major histocompatibility class II molecules. Here, we describe the cellular and molecular aspects of these cognate T-B interactions, and highlight exceptional cases, especially those arising at intestinal lymphoid organs, at which T cells provide help to B cells in an atypical manner, independent of T cell specificity.     

Differential migration of in vivo primed B and T lymphocytes to lymphoid and non-lymphoid organs

Our study describes tissue-specific migration of T and B cells during a localized anti-viral immune response. After mouse mammary tumor virus (MMTV) injection, B lymphocytes of the draining lymph node become infected and present a retroviral superantigen to CD4(+) T lymphocytes. Infected B cells receive superantigen-mediated help in a fashion comparable to classical immune responses. To investigate the fate of T and B lymphocytes that had interacted via cognate help in the same peripheral lymph node microenvironment we adoptively transferred them into naive recipients. Here we show that MMTV-infected B cells and superantigen-stimulated T cells were programmed to migrate to distinct sites of the body. Plasmablasts but not T cells migrated to the mammary gland and activated alpha4beta1 integrins were found to have a crucial role in the migration to the mammary gland. In contrast, T cells had a much higher affinity for secondary lymphoid organs and large intestine.This demonstrates that upon antigen-driven B and T lymphocyte interaction in the local draining lymph node a subset-specific homing program for B and T lymphocytes is induced.