Hemopoietic tissue in the adult newt,Notopthalmus viridescens

The presence of developmental stages of lymphocytes and their precurors, as revealed by serial and thin sections of hemopoietic organs of normal adult newts (Notopthalmus viridescens) suggests that lymphopoiesis is limited to the thymus, medulla of the spleen and, to a lesser degree, the intestine. Stromal cells, small lymphocytes, granulocytes, mature erythrocytes and melanocytes were observed either within or near the parenchyma of the thymus. The urodele thymus differs from the thymus of anurans and higher vertebrates in that it lacks a cortex and a medulla, myoid cells and Hassall's corpuscles.     

Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure

This study identifies environmental predictors of the condition of two introduced tilapia species (Oreochromis leucostictus and Tilapia zillii) that are known to have divergent trophic niches (planktivore and herbivore, respectively) in 17 crater lakes in western Uganda. We asked whether fish condition differs among lakes characterized by differences in fishing pressure and catchment deforestation; and we related relative condition factor to gradients of environmental variation across lakes. Lakes characterized by severe catchment deforestation tended to be lakes with high fishing pressure, so it was difficult to explore independent and interactive effects. However, mean relative condition factor was higher in populations with high fishing pressure compared to populations with low fishing pressure for both O. leucostictus and T. zillii. The condition of O. leucostictus populations was higher in lakes with severely deforested catchments; but mean relative condition factor of T. zillii did not differ between deforestation categories. Principal components analysis (PCA) was used to describe the major environmental gradients of variation among the lakes; and PCA factor scores were regressed against relative fish condition. The association between fish condition and environmental gradients was stronger for O. leucostictus than for T. zillii. For O. leucostictus, fish condition was related to PC1 (43% of the variance) and factors that loaded most heavily included Chl-a, water transparency, lake area and depth, suggesting higher condition in lakes characterized by higher primary productivity and smaller size. For T. zillii, PC3 (11%) was the only axis related to fish condition; and factors that loaded most heavily included lake area (positive), and conductivity and total nitrogen (negative). Some of the larger lakes are characterized by higher availability of macrophytes that may positively affect the food base for T. zillii.     

Feeding ecology of Oreochromis niloticus (Linnaeus) & Tilapia Zillii (Gervias) in a Nile canal

Fish stomachs, 1149 for Tilapia zillii and 1698 for Oreochromis niloticus, were collected from April 1984 till April 1985 from a Nile canal in the Egyptian delta. Both species showed a significant overlap of diet (Schoener's index) among individuals ranging from 12 to 17.9 cm standard length. Outside this range differences in the importance of food of animal origin occurred. Macrophytes were the main food of O. niloticus and aquatic insects of the food of T. zillii. This initial diet overlap may have contributed to irregularity in the increase of full stomachs with increasing length, and to a decline of the stomach index (SI = stomach weight × 100/fish weight) with increase in length in O. niloticus. The stomach of either species correlated significantly with water temperature, but with daily photoperiod in O. niloticus only.     

The effects of age, thymectomy, and HIV Infection on alpha and beta TCR excision circles in naive T cells

Due to homeostasis total naive T cell numbers remain fairly constant over life despite a gradual involution of the thymus. The contribution of the thymus to maintaining naive T cell pools is typically measured with TCR excision circles (TRECs) that are formed in thymocytes. The mechanisms underlying thymic involution are poorly understood. Some data suggest that thymocytes undergo fewer divisions in old (small) than young (large) thymi, and other data suggest that the number of TRECs per thymocyte is independent of age. If thymic involution were associated with a decreased number of divisions of the thymocytes, this would markedly complicate the interpretation of TREC data. To study this we develop a mathematical model in which the division rate of thymocytes decreases with increasing age. We describe the dilution of TRECs formed during the arrangement of both chains of the TCR by division of thymocytes, recent thymic emigrants, and mature naive T cells. The model behavior is complicated as TREC contents in naive T cells can increase with age due to decreased dilution in the thymus. Because our model is consistent with current data on the effects of age and thymectomy on TRECs in peripheral T cells, we conclude that aging may well affect thymocyte division, which markedly complicates the interpretation of TREC data. It is possible, but more difficult, to let the model be consistent with the rapid changes in alpha and beta TRECs observed shortly after HIV infection.     

Declining expression of a single epithelial cell‐autonomous gene accelerates age‐related thymic involution

Age‐related thymic involution may be triggered by gene expression changes in lymphohematopoietic and/or nonhematopoietic thymic epithelial cells (TECs). The role of epithelial cell‐autonomous gene FoxN1 may be involved in the process, but it is still a puzzle because of the shortage of evidence from gradual loss‐of‐function and exogenous gain‐of‐function studies. Using our recently generated loxP‐floxed‐FoxN1(fx) mouse carrying the ubiquitous CreER^T (uCreER^T) transgene with a low dose of spontaneous activation, which causes gradual FoxN1 deletion with age, we found that the uCreER^T‐fx/fx mice showed an accelerated age‐related thymic involution owing to progressive loss of FoxN1⁺ TECs. The thymic aging phenotypes were clearly observable as early as at 3–6 months of age, resembling the naturally aged (18–22‐month‐old) murine thymus. By intrathymically supplying aged wild‐type mice with exogenous FoxN1‐cDNA, thymic involution and defective peripheral CD4⁺ T‐cell function could be partially rescued. The results support the notion that decline of a single epithelial cell‐autonomous gene FoxN1 levels with age causes primary deterioration in TECs followed by impairment of the total postnatal thymic microenvironment, and potentially triggers age‐related thymic involution in mice.     

Consequences of interactions between thymic lymphoid and epithelial cells in vitro

A 24-hour co-cultivation of thymocytes and epithelial cells taken from human thymus results in mutual activation of epitheliocytes and thymocytes, as well as in apoptosis of thymocytes. The apoptosis can also be induced by a cultural supernatant of the thymic-epithelial cells, its level being lower, however, than in the co-culture. Thymocyte death and elimination develop faster in a co-culture with allogeneic thymic epithelial cells.     

Identification of subsets of proliferating low Thy 1 cells in thymus cortex and medulla

Subsets of proliferating thymocytes were identified in the normal mouse thymus by in vivo labeling with [³H]TdR and by cell separation according to relative amounts of Thy 1 antigen. In order to resolve apparent discrepancies in the literature, parenteral and topical application of [³H]TdR were compared as labeling methods for dividing thymocytes, and limited complement lysis and fluorescence-activated cell sorting were compared as separation principles for high Thy 1 and low Thy 1 thymocyte subsets. The separated cells were further characterized by immunofluorescence for terminal deoxynucleotidyltransferase (TdT), which normally is restricted to cortical thymocytes, and for H2 alloantigens, which are preponderant on medullary thymocytes. Four subsets of proliferating cortical thymocytes were identified after application of [³H]TdR to the thymus capsule. The major subset, which comprised about 92% of dividing cortical thymocytes, had a high Thy 1, low H2 phenotype. Most were also TdT + ve. The three minor subsets of proliferating cortical thymocytes each had a low Thy 1 phenotype, but differed according to H2 and TdT markers. Systemic injection of [³H]TdR also labeled the above subsets of dividing cortical thymocytes, but in addition it detected a subset of proliferating low Thy 1, low H2, TdT — ve cells in the thymus medulla. The latter subset comprised about one-third of the pool of proliferating low Thy 1 cells. In their aggregate the four subsets of low Thy 1 cells constituted approximately 13% of total proliferating thymocytes and 1.1% of total thymocytes. The identification of discrete subsets of proliferating low Thy 1 cells in the thymus cortex as well as in the thymus medulla is compatible with the hypotheses that all thymocytes are descended from low Thy 1 precursors and that separate precursor cell subsets exist for cortical and medullary thymocytes.     

Cyclosporine and the thymus: influence of irradiation and age on thymic immunopathology and recovery

With the proper experimental conditions, previous studies have demonstrated that syngeneic and autologous radiation chimeras treated with cyclosporine (CsA) routinely develop a syndrome resembling graft-vs-host disease (GVHD) after CsA is discontinued. The thymus is clearly important in the pathogenesis. Thymectomy prior to CsA prevents the development of syngeneic GVHD and the process can be adoptively transferred via thymocytes. The thymus, however, must be within the field of irradiation and the animal must be young. Here we examine how irradiation and advanced age influence the thymic immunopathologic changes induced by CsA and influence the recovery post-CsA. Young LEW rats, with or without pre-CsA mediastinal irradiation, demonstrate a marked involution of the thymic medulla with associated loss of medullary epithelium, Hassall's corpuscles, class II antigen expression, and maturation of thymocytes. While the control group underwent rapid and complete regeneration of the medulla post-CsA, however, the medullary changes in the irradiated group were prolonged or permanent. Most of these animals had changes of chronic GVHD. Older LEW rats had a more prominent medulla prior to CsA. In contrast to younger rats, the medulla did not show significant involution with CsA. While the Hassall's corpuscles disappeared, the medullae still had fusiform epithelium, dendritic cells, and class II antigen expression. Phenotype stains demonstrated many mature-appearing CD4+/CD8- lymphocytes. In light of evidence indicating the importance of the medullary microenvironment to the maintenance of self tolerance, the medullary effects of CsA are most likely essential to the development of autoimmunity. Young rats rapidly lose the ability to maintain tolerance. While unirradiated rats rapidly reestablish the proper microenvironment following CsA, irradiated rats have a prolonged loss. Older rats may resist the development of autoimmunity by retaining the medullary microenvironment.     

Epithelial cell heterogeneity in mammalian thymus: Monoclonal antibody to high molecular weight keratins exclusively binds to Hassall''s corpuscles

Summary Hassall's corpuscles represent a subset of medullary thymic epithelial cells whose origin and function within the thymus still remain largely unknown. The present study shows that Hassall's corpuscles can be defined by their intracellular content in specific keratin subunits. Two monoclonal anti-keratin antibodies were used: KL1, directed to high molecular weight keratins, and KL4, specific for high and medium molecular weight polypeptides.In vivo, KL1 exclusively binds to Hassall's corpuscles of five mammalian species including mouse, rat, guinea-pig, rabbit and pig. Thus KL1 appears as an exclusive marker of Hassall's corpuscles in a large number of mammals.In vitro, thymic epithelial cells gave rise in certain species to Hassall's corpuscles. In contrast to itsin vivo reactivity, KL1 never labelled Hassall's corpuscles developedin vitro. These data strongly support the following conclusions: (1) Hassall's corpuscles derive from medullary epithelial cells; (2) they represent advanced stages of thymic epithelial maturation; (3) thymic epithelial cell differentiation is impairedin vitro. Furthermore, this study provides additional evidence that thymic epithelium heterogeneity reflects different stages in epithelial maturation.     

FATE OF THYMOCYTES: STUDIES WITH 125I-IODODEOXYURIDINE AND 3H-THYMIDINE IN MICE

Cortical thymocytes of young adult mice were labeled in situ with radioactive DNA precursors. As a result of cell emigration and cell death, total thymic radioactivity decreased within 8 days to 10% or less of that present on day 1. Accumulation of thymic migrants in peripheral lymphoid organs was estimated by computing the net thymus-derived radioactivity in these tissues. Thymic cell death was assessed by comparing values obtained with ¹²⁵I-UdR to those acquired with ³H-TdR. The results indicate that cortical thymocytes migrate to the spleen, mesenteric lymph node, femurs and intestine; nevertheless, only a small fraction of the activity originally present in the thymus was recovered in these organs; the vast majority of newly formed cortical thymocytes apparently die after a relatively short life span. Exclusive of the fraction which dies in situ, evidence for thymocyte death is seen in bone marrow; however, most migrants appear to terminate in the intestine.     

Feeding habits and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake,central China

The diet and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91–539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.     

Transgenic Expression of MicroRNA-181d Augments the Stress-Sensitivity of CD4+CD8+ Thymocytes

Physiological stress resulting from infections, trauma, surgery, alcoholism, malnutrition, and/or pregnancy results in a substantial depletion of immature CD4⁺CD8⁺ thymocytes. We previously identified 18 distinct stress-responsive microRNAs (miRs) in the thymus upon systemic stress induced by lipopolysaccharide (LPS) or the synthetic glucocorticoid, dexamethasone (Dex). MiRs are short, non-coding RNAs that play critical roles in the immune system by targeting diverse mRNAs, suggesting that their modulation in the thymus in response to stress could impact thymopoiesis. MiR-181d is one such stress-responsive miR, exhibiting a 15-fold down-regulation in expression. We utilized both transgenic and gene-targeting approaches to study the impact of miR-181d on thymopoiesis under normal and stress conditions. The over-expression of miR-181d in developing thymocytes reduced the total number of immature CD4⁺CD8⁺ thymocytes. LPS or Dex injections caused a 4-fold greater loss of these cells when compared with the wild type controls. A knockout mouse was developed to selectively eliminate miR-181d, leaving the closely spaced and contiguous family member miR-181c intact. The targeted elimination of just miR-181d resulted in a thymus stress-responsiveness similar to wild-type mice. These experiments suggest that one or more of three other miR-181 family members have overlapping or compensatory functions. Gene expression comparisons of thymocytes from the wild type versus transgenic mice indicated that miR-181d targets a number of stress, metabolic, and signaling pathways. These findings demonstrate that selected miRs enhance stress-mediated thymic involution in vivo.     

Biosynthesis of glycosaminoglycans by epithelial and lymphocytic components of murine thymus

Interactions between the epithelial and lymphocytic components of the thymus are required for T cell maturation, yet the molecular bases for these interactions remain elusive. In the development and function of other endodermally derived organs, glycosaminoglycan-containing proteins are known to play a critical role. In contrast, virtually nothing is known about the macromolecules that are major constituents of thymic interstitial spaces. For these reasons, we undertook metabolic labeling studies in vitro with D-(6-3H)glucosamine and 35SO4(-2) to begin to characterize systematically the relative amounts and types of glycosaminoglycans made by enriched subpopulations of cells within the thymus. Hydrocortisone, which depletes the thymus of 90% of its lymphocytes, was used both to enrich for epithelium-derived glycoconjugates and to determine if significant alterations in glycoconjugate metabolism accompany drug-induced premature thymic involution. Results indicate: 1) glycosaminoglycans account for a substantial proportion of the total glycoconjugates synthesized by both thymocytes and epithelium; 2) Glycosaminoglycans show a tissue-specific distribution. Hyaluronic acid is the major glycosaminoglycan synthesized by thymic epithelium, whereas it accounts for less than 15% of the total glycosaminoglycans made by thymocytes; 3) Similar proportions of sulfated glycosaminoglycans are made by thymic epithelium and thymocytes. Chondroitin sulfates predominate (75 to 90%) over heparan sulfates (10 to 25%). Chondroitin sulfates from both nonstimulated thymocytes and epithelium are nearly exclusively sulfated at the 4-position of their N-acetylgalactosamine residues; 4) The major high m.w. glycoconjugate of thymocytes, however, is nonsulfated and is resistant to pronase, hyaluronidase, chondroitinase ABC, nitrous acid, keratanase, and neuraminidase; 5) Although hydrocortisone treatment causes a dramatic inhibitory effect on the incorporation of radioactivity into smaller oligosaccharide side-chains by "cortisone-resistant" thymocytes, the drug exerts negligible effects on the metabolism of glycoconjugates by epithelium. These data, which quantify and categorize the complex arrays of glycoconjugates synthesized by the major cell types of the thymus, establish the necessary foundations for further investigations into the functional roles of these glycoconjugates in thymic epithelium-induced maturation of T lymphocytes.     

Indomethacin inhibits thymic involution in mice with streptozotocin-induced diabetes

Diabetes is chronic disease that is accompanied by a rapid thymus involution. To investigate the factors responsible for thymic involution in a model of STZ-induced diabetes, mice were injected with STZ alone or in combination with the cyclooxygenase 2 inhibitor indomethacin (INDO). Thymus weight, glycemia and serum corticosterone were measured, and apoptosis in thymus and thymocyte cultures was analyzed by flow cytometry. Although earlier studies report that streptozotocin (STZ) is toxic to lymphoid tissues, in our experiments even massive doses of STZ did not negatively affect thymocyte cultures. Cultured thymocytes also seemed unaffected by high glucose concentrations, even after 24 h of exposure. Administration of INDO concomitantly with STZ reduced thymic involution but did not prevent the onset of hyperglycemia or reduce established hyperglycemia. When INDO was given before STZ, the same degree of thymic involution occurred; however, hyperglycemia was reduced, although normoglycemia was not restored. INDO also reduced serum corticosterone. Because thymocytes are known to be sensitive to glucocorticoids, this finding suggests that cyclooxygenase 2 inhibition may retard thymic involution by reducing serum glucocorticoids. In conclusion, our results show that STZ and hyperglycemia are not toxic to thymocytes and that cyclooxygenase 2-mediated mechanisms are involved in thymic involution during diabetes.     

Histological changes of the mouse thymus during involution and regeneration following administration of hydrocortisone

Summary A histological study has been made of the thymus in mice during acute involution and regeneration following administration of hydrocortisone. The cortex undergoes remarkable changes in the microscopic structure during involution and regeneration. During involution the lymphocytes in the cortex rapidly decrease and are removed. Then a rapid replacement of lymphocytes occurs during regeneration. On the basis of formation and repopulation of lymphocytes the regenerative process of the cortex is divided into seven phases. The reconstitution of the cortex proceeds more rapidly in females than in males. Newly formed lymphocytes take origin from the mesenchymal cells in the cortex. Such mesenchymal cells become distinguishable from epithelial reticular cells during involution. They appear to engulf destroyed lymphocytes and debris during involution and then transform into immature lymphoid cells during early regeneration. The findings may support the recent reutilization concept that destroyed lymphocytes are phagocytized and reutilized by reticular cells in heteroplastic differentiation into immature lymphoid cells. In the cortex PAS-positive sudanophilic cells which are derived from the perivascular and subcapsular connective tissue appear with involutionary changes. They become gradually reduced again with progress of the regeneration of the cortex. During involution the medulla are temporarily filled with lymphocytes migrated from the cortex. The epithelial reticular cells in the medulla are found grouped in cords or clumps in the severely involuted thymus. In the medulla there are two types of PAS-positive epithelial reticular cells; one contains a large, colloid-like, PAS-positive inclusion within the cytoplasm and the other has cytoplasm diffusely filled with PAS-positive substance. During involution and early regeneration, the former type increases while the other shows almost no significant changes. Hassall's corpuscles somewhat increase in frequency during involution and early regeneration.     

A review of length–weight relationships of fish from the Segura River basin (SE Iberian Peninsula)

We present the relationships between fork length and total weight for 14 fish species from the Segura River basin (southeastern Spain): Barbus sclateri, Chondrostoma polylepis, Gobio lozanoi, Aphanius iberus, Micropterus salmoides, Lepomis gibbosus, Carassius auratus auratus, Cyprinus carpio carpio, Sander lucioperca, Gambusia holbrooki, Liza ramado, Mugil cephalus, Atherina boyeri and Pomatoschistus marmoratus. Significant length–weight relationships were found for all species. The values of the exponent b of the length–weight relationships ranged from 3.82 for Sander lucioperca to 2.59 for Micropterus salmoides.     

Induction of Interleukin 2-Responsiveness in Thymocytes of the Transgenic Mice Carrying lck-Transgene

The role of lck gene in T cell proliferation and differentiation was investigated with transgenic mice carrying human lck cDNA whose expression was regulated by the promoter of mouse H-2K^b and the enhancer element of mouse IgH. RNase protection assay revealed that the lck transgene was expressed in the thymus and spleen, whereas immunoblot analysis demonstrated that amounts of p56^lck in freshly isolated lymphoid organs were almost equal between transgenic mice and negative littermates. Cell-surface marker analyses of the thymocytes and peripheral lymphocytes revealed no remarkable difference between both groups. Notable finding is that the thymocytes from transgenic mice showed a significant proliferative response to the stimulation with IL-2, but not the thymocytes from negative littermates. Further analysis revealed that CD4⁺8^– single positive thymocytes proliferated in response to IL-2. While surface expression levels of IL-2Rα and IL-2Rβ of these CD4⁺8^– thymocytes from transgenic and control mice were almost equal before stimulation with IL-2, the expression of IL-2Rβ was induced only in transgenic thymocytes after stimulation with IL-2. Immunoblot analysis demonstrated that the expression of p56^lck of transgenic thymocytes was not down-reguated at 4 hr after stimulaion with IL-2, whereas p56^lck of control ones were not detectable any more at 4 hr after stimulation with IL-2. Moreover, in vitro kinase assay substantiated such unchanged expression of p56^lck in the thymocytes from transgenic mice: the kinase activities of p56^lck did not decrease in thymocytes from transgenic mice after stimulation with IL-2, while kinase activities of control ones were significantly down-regulated by stimulation of IL-2. These results suggested that a significant proliferative response found in the thymocytes from lck-transgenic mice after the stimulation with IL-2 was caused by a constitutive expression of p56^lck in these thymocytes even after the stimulation. Our findings, therefore, support a possibility that p56^lck may play a role in the IL-2R-mediated signaling system in CD4⁺8^– thymocytes.     

Differential gene expression in CD3e- and RAG1-deficient thymuses: definition of a set of genes potentially involved in thymocyte maturation

 A set of 3000 mouse thymus cDNAs was analyzed by extensive measurement of expression using complex-probe hybridization of DNA arrays ("quantitative differential screening"). The complex probes were initially prepared using total thymus RNA isolated from C57BL/6 wild-type (WT), CD3e- and RAG1-deficient mice. Over 100 clones displaying over- or under-expression by at least a factor of two between WT and knockout (KO) thymuses were further analyzed by measuring hybridization signatures with probes from a wide range of KO thymuses, cell types, organs, and embryonic thymuses. A restricted set of clones was selected by virtue of their expression spectra (modulation in KO thymuses and thymocytes, lymphoid cell specificity, and differential expression during embryonic thymus development), sequenced at one extremity, and compared to sequences in databases. Clones corresponding to previously identified genes (e.g., Tcrβ, Tcf1 or CD25) showed expression patterns that were consistent with existing data. Ten distinct clones corresponding to new genes were subjected to further study: Northern blot hybridization, in situ hybridization on thymus sections, and partial or complete mRNA sequence determination. Among these genes, we report a new serine peptidase highly expressed in cortical epithelial cells that we have named thymus-specific serine peptidase (TSSP), and an acidic protein expressed in thymocytes and of unknown function that we have named thymus-expressed acidic protein (TEAP). This approach identifies new molecules likely to be involved in thymocyte differentiation and function. Received: 3 June 1999 / Revised: 3 August 1999