Functional and phenotypic analysis of thymic B cells: role in the induction of T cell negative selection.

The phenotype of mouse thymic B cells and their capacity to induce T cell negative selection in vitro were analyzed. Thymic B cells expressed B cell markers such as IgM, Fc gamma receptor, CD44, heat-stable antigen, LFA-1 and CD40. In addition, they were positive for the activation molecule CD69 and displayed high levels of B7-2. Although thymic B cells expressed CD5 on their surface, no CD5-specific mRNA was detected. Moreover, thymic B cells induced a stronger deletion of TCR-transgenic (TG) thymocytes than splenic B cells, which had low CD69 and B7-2 levels. Interestingly, CD40-activated splenic B cells up-regulated CD69 and B7-2 and acquired a capacity to induce T cell deletion comparable to that of thymic B cells. Moreover, thymic B cells from CD40-deficient mice displayed lower CD69 and B7-2 levels than control thymic B cells, and lower capacity to induce the deletion of TCR TG thymocytes. These results support the hypothesis that CD40-mediated activation of thymic B cells determines a high efficiency of antigen presentation, suggesting that within the thymus B cells may play an important role in the elimination of autoreactive thymocytes.     

Effects of peroxisome proliferators on the thymus and spleen of mice

The effects of peroxisome proliferators on the immune system of male C57B1/6 mice have been investigated. Significant atrophy of the thymus and spleen was observed in animals treated with potent peroxisome proliferators (e.g. perfluorooctanoic acid (PFOA), di(2-ethylhexyl)phthalate (DEHP), Wy-14643 and nafenopin), whereas the effects of a moderate peroxisome proliferator (i.e. acetylsalicylic acid (ASA)) were relatively weak. The time course of thymic and splenic atrophy caused by PFOA was found to resemble the time course of the increase in liver weight and of peroxisome proliferation. Analysis of the numbers and phenotypes of thymocytes and splenocytes from PFOA-treated mice revealed the following: (i) the numbers of thymocytes and splenocytes were decreased > 90% and about 50%, respectively, by PFOA treatment; (ii) although all populations of thymocytes were decreased, the immature CD4+CD8+ population was decreased most dramatically; (iii) the numbers of both T and B cells in the spleen were decreased by PFOA treatment. Analysis of the cell cycle of thymocytes indicated that the thymic atrophy caused by PFOA in mice results, at least in part, from inhibition of thymocyte proliferation. Interestingly, in vitro exposure to PFOA for up to 24 h did not produce analogous effects in either thymocytes or splenocytes. Thus, the thymic and splenic atrophy caused by PFOA appears to involve an indirect pathway.     

Chicken thymocyte antigen which participates in cell proliferations of thymocytes and tumour-derived lymphoid cell lines

A novel antigen on chicken thymocytes was defined by CETHB1 and CETH46 monoclonal antibodies (mAbs) that were prepared against chick embryonic thymocytes. CETHB1 and CETH46 mAbs recognized different epitopes on the same membrane antigen (molecular weight: 76.2 kDa). These mAbs reacted with >80% of thymocytes of 14-day-old embryos to 8-week-old chickens. Almost all splenocytes, peripheral blood lymphocytes and bursa cells were negative, and only 7.7% of bone marrow cells were positive for both antibodies. In two-colour analysis with mAbs reacting to T cell markers (CD4 or CD8), most CETHB1 positive cells were CD4 (- )CD8 (-) or CD4 (+) CD8 (+) . However, a proportion of CD4 (+) CD8 (-) and CD4 (- )CD8 (+) cells were negative for CETHB1 mAb. The proportion of thymocytes reacting with CETHB1 in chickens immunosuppressed by cyclophosphamide treatment increased gradually in parallel with the restoration of the thymus. An increase of CETHB1-positive cells was observed in thymocytes stimulated with Con A. Hence, it seems that the CETHB1 antigen expression on thymocytes is influenced by the thymic micro-environment and that the antigen may take part in thymic differentiation. Interestingly, CETHB1 antigen was expressed not only on T cell tumour-derived lymphoid cell lines, but also B-lymphoma-derived cell lines. The antigen expressions on these cell Unes were observed only in the prohierative phase of the cells. Hence, the molecule which reacted with CETHB1 may be an antigen commonly expressed on lymphoma cells and may be involved in cell proliferation.     

小鼠胸腺基质细胞单抗对胸腺细胞及脾细胞增殖的抑制作用

试验两种大鼠抗小鼠胸腺基质细胞（ＭＴＳＣ）ＭｃＡｂｓＰｆ１８－３、Ｒｓ２１－Ｃ６的生物作用。Ｐｆ１８－３ＭｃＡｂ识别分子表达于胸腺细胞、脾脏Ｔ及Ｂ细胞；Ｒｓ２１－Ｃ６只表达于ＭＴＳＣ。加Ｐｆ１８－３或Ｒｓ２１－Ｃ６于ＭＴＥＣＩ与胸腺细胞或脾细胞的体外培养中，在ＣｏｎＡ存在及不存在下，均可抑制ＭＴＥＣ１诱导胸腺细胞及脾细胞的增殖作用。ＣｏｎＡ活化下，其对胸腺细胞增殖的抑制率Ｐｆ１８－３为９６％；Ｒｓ２１－Ｃ６为９１％。对脾细胞的抑制率Ｐｆ１８－３为７５％；Ｒｓ２１－Ｃ６为５１％。Ｐｆ１８－３对单纯ＣｏｎＡ活化的胸腺细胞增殖也有显著的抑制作用，而Ｒｓ２１－Ｃ６无此作用。包被于平皿的固相Ｐｆ１８－３ＭｃＡｂ，对胸腺细胞、脾细胞均有轻度但显著的促增殖作用。故Ｐｆ１８－３ＭｃＡｂ识别的抗原分子（及其配基）参与Ｔ细胞的活化过程。鉴于Ｐｆ１８－３＋细胞的分布有其特异性，分析此抗原分子的功能有重要的意义。     

Effect of murine thymic epithelial cell line (MTEC1) on the functional expression of CD4(+)CD8(-) thymocyte subgroups

To determine the effect of thymic stromal cells on the functional maturation of CD4 single-positive (SP) thymocytes, the functional status of isolated CD4 SP thymocyte subgroups was investigated by means of cell proliferation and cytokine production in response to concanavalin A (Con A) prior and after co-culturing with a murine thymic epithelial cell line (MTEC1). Mouse medullary CD4 SP thymocytes were phenotypically divided into seven discrete subgroups predicted to reflect the maturation pathway from newly emerging CD4 SP thymocytes to terminally differentiated cells. For functional analysis, six major subgroups (6C10(+)CD69(+), 6C10(-)CD69(+), 6C10(-)CD69(-)3G11(+)Qa-2(-), 6C10(-)CD69(-)3G11(+)Qa-2(+), 6C10(-)CD69(-)3G11(-)Qa-2(-) and 6C10(-)CD69(-)3G11(-)Qa-2(+)) cells were isolated and their functional status in response to Con A stimulation assessed. A functional hierarchy is revealed among these subgroups, consistent with their phenotypic maturation status, which may imply that these cells undergo a functional maturation process within thymic medulla. The function of cytokine production by CD4 SP thymocytes is acquired in a stepwise manner from a low to high level and characterized by T(h)0-type cytokines in the main stream of differentiation pathway. However, a minor subgroup that appeared at the late stage as 3G11(-)6C10(-) cells was biased to produce T(h)2-type cytokines. Nevertheless, the functional capacity of the final two Qa-2(+) subgroups of CD4 SP thymocytes was still significantly lower than that of spleen CD4(+) T cells. After co-cultivation with MTEC1 cells, four subgroups of TCRalphabeta(+)CD4(+)CD8(-) thymocytes exhibited significantly higher levels of proliferation capability and modulation in cytokine production capability. However, co-culturing with MTEC1 cells did not change the pattern of T(h)0- or T(h)2-like cytokine production by respectively medullary CD4 SP thymocyte subgroups nor could MTEC1 induce CD4 SP thymocytes to secrete T(h)1-type cytokines. The results suggest that MTEC1 can regulate the functional status of these thymocyte subgroups.     

Glucocorticoid (GC) sensitivity and GC receptor expression differ in thymocyte subpopulations

Positive and negative selection steps in the thymus prevent non-functional or harmful T cells from reaching the periphery. To examine the role of glucocorticoid (GC) hormone and its intracellular receptor (GCR) in thymocyte development we measured the GCR expression in different thymocyte subpopulations of BALB/c mice with or without previous dexamethasone (DX), anti-CD3 mAb, RU-486 and RU-43044 treatment. Four-color labeling of thymocytes allowed detection of surface CD4/CD8/CD69 expression in parallel with intracellular GCR molecules by flow cytometry. Double-positive (DP) CD4+CD8+ thymocytes showed the lowest GCR expression compared to double-negative (DN) CD4-CD8- thymocytes and mature single-positive (SP) cells. DX treatment caused a concentration-dependent depletion of the DP cell population and increased appearance of mature SP cells with reduced GCR levels. GCR antagonists (RU-486 or RU-43044) did not influence the effect of DX on thymocyte composition; however, RU-43044 inhibited the high-dose GC-induced GCR down-regulation in SP and DN cells. GCR antagonists alone did not influence the maturation of thymocytes and receptor numbers. Combined low-dose anti-CD3 mAb and DX treatment caused an enhanced maturation (positive selection) of thymocytes followed by the elevation of CD69+ DP cells. The sensitivity of DP thymocytes with a GCRlow phenotype to GC action and the ineffectiveness of the GCR antagonist treatment may reflect a non-genomic GC action in the thymic selection steps.     

T cell receptor excision circle assessment of thymopoiesis in aging mice

Signal joint T cell receptor delta (TCRD) excision circles (TRECs) are episomal DNA circles generated by the DNA recombination process that is used by T lymphocytes to produce antigen-specific alpha/beta T cell receptors. Measurement of TRECs in thymocytes and peripheral blood T cells has been used to study thymus output in chickens and humans. We have developed a real-time quantitative-PCR assay for the specific detection and quantification of mouse TCRD episomal DNA circles excised from the TCRA locus during TCRA gene rearrangement (mTRECs). We found that the mouse TCRD TRECs detected with this assay were predominantly in na?ve phenotype CD4(+) and CD8(+) T cells. In a series of aged mice (range 6-90-week-old) we determined the absolute number of thymocytes and the number of molecules of mTRECs/100,000 thymocytes. We found that the absolute number of thymocytes dramatically decreased with age (P<0.05) and that molecules of mTREC/100,000 thymocytes also declined with mouse age (P<0.05). Splenocytes were isolated from aging mice and the frequency of na?ve phenotype CD4 and CD8 cells determined. There was a significant drop in both CD4 and CD8 na?ve peripheral T cells in the aged mice over time. mTREC analysis in purified CD4(+) and CD8(+) splenocytes demonstrated a constant level of mTRECs in the CD4 compartment until age 90 weeks, while the mTRECs in the CD8 compartment fell with age (P<0.05). By combining the mouse TREC assay with T cell phenotypic analysis, we demonstrated that IL-7 administration to young mice induced both increased thymopoiesis and peripheral T cell proliferation. In contrast, IL-7 treatment of aged mice did not augment thymopoiesis, nor induce expansion of splenic T cells. Thus, thymus output continues throughout murine adult life, and the thymic atrophy of aging in mice is not reversed by administration of IL-7.     

Discrimination between maintenance- and differentiation-inducing signals during initial and intermediate stages of positive selection

As well as signaling through the αβ T cell receptor complex, positive selection of immature CD4⁺ 8⁺ thymocytes involves additional ill-defined accessory interactions provided by thymic epithelial cells. Here, we have isolated CD4⁺ 8⁺ thymocytes at a pre-positive selection stage of development (TCR^? CD69^? 4⁺ 8⁺ cells), or after initiation of positive selection (CD69⁺ 4⁺ 8⁺ cells), from mice where the normal lifespan of thymocytes is extended by the presence of a bcl-2 transgene, to allow us to discriminate between requirements for maintenance and differentiation signals during positive selection. We find that MHC class II⁺ thymic epithelial cells drive positive selection of TCR^? CD69^? 4⁺ 8⁺ bcl-2 tg thymocytes to the CD4⁺ and CD8⁺ stage, while no such mature subsets are observed when thymocytes are cultured alone or with major histocompatibility complex (MHC) class II⁺ salivary epithelial cells. However, CD4⁺ 8⁺ cells remain in such cultures in considerable numbers, and retain the potential for positive selection if re-cultured with thymic epithelium, suggesting that thymic epithelial cells provide specific differentiation-inducing signals for positive selection. In contrast, intermediate CD69⁺ 4⁺ 8⁺ thymocytes show some capacity for phenotypic conversion in the absence of thymic stromal cells although strikingly the single-positive CD4⁺ and CD8⁺ cells generated are not functionally competent. Finally, we show that prior culture of thymic epithelial cells under monolayer conditions abrogates their ability to support the initiation of positive selection, suggesting that the epithelial cell molecules necessary for the provision of differentiation signals during positive selection are down-regulated under such conditions.     

Properties of human thymic B cells.

B cells, distinct from those seen in myasthenia gravis, are present in normal human thymic medulla, concentrated around the Hassall's corpuscles. We have shown that they constitute 33 +/- 4.8% of the total cells in the thymic medulla. In tissue sections they were often seen to have rosettes of thymocytes around them, a relationship which was maintained when the cells were isolated from the thymus. Thymic B cells expressed cytoplasmic immunoglobulins IgD, IgM and IgG but only rarely IgA. Unlike murine thymic B cells, human thymic B cells were CD5-. Freshly isolated thymic B cells were activated cells, but they rapidly became quiescent and died in culture over a 10-day period unless stimulated with mitogens. Thymic B cells responded to polyclonal B-cell activators SAC and TPA and when stimulated, maintained their relationship with thymocytes. Electron microscopic studies showed that two morphologically different thymocyte populations associated with the B cells. The plasma membranes of larger thymocytes were juxtaposed to the B-cell membrane, but smaller thymocytes with darker cytoplasm were associated with the B cells via cytoplasmic strands. Studies in mice have suggested that B cells are involved in thymic negative selection. The close association between activated B cells and thymocytes observed in this study supports this hypothesis.     

Five novel antigens illustrate shared phenotype between mouse thymic stromal cells, thymocytes, and peripheral lymphocytes.

Previously we characterized by immunohistology a group of rat anti-mouse thymic stromal mAbs (MTS 12, 32, 33, 35, and 37), which recognized novel plasma membrane determinants on both thymic stromal cells (TSCs) and thymocytes. The present study investigates in more detail this incidence of shared phenotype by an extensive flow cytometric analysis of MTS mAb reactivity on TSCs, thymocyte subsets, peripheral lymphocytes, and bone marrow cells. Examination of freshly isolated or cultured heterogeneous TSCs and TSC clones confirmed that the mAb identified plasma membrane molecules on distinct subsets of these cells. All but MTS 12 reacted with epithelial cells. Triple-labelling illustrated that MTS 32, 33, and 37 were also reactive with more than 90% of total thymocytes, but varied in their distribution on the four major CD4 and CD8 defined subsets. MTS 12, staining with thymic vascular endothelium by immunohistology, labelled more than 95% of each subset. MTS 35 reactivity in each subset correlated strongly with only the immature populations. Examination of peripheral lymphocytes by triple- and double-labelling unexpectedly showed that MTS 33, 35, and 37 did not recognize peripheral T cells but labelled all B cells. MTS 32 was negative for B cells, but positive for all CD8+ T cells, yet only a subset of CD4+ T cells. Further, MTS 33, 35, and 37 were present on a significant percentage of bone marrow cells. MTS 12 reacted with virtually all peripheral T and B cells, and about 50% bone marrow leukocytes. Collectively these results reveal the same novel epitopes on different thymic cell types and subsets thereof, highlighting specific similarities between cells of apparently diverse lineages. These findings may be of importance in the delineation of intercellular communications within the thymus and emphasize the integrated nature of the microenvironment in this organ.     

Immunologic immaturity, but high IL-4 productivity, of murine neonatal thymic CD4 single-positive T cells in the last stage of maturation

To determine the levels of maturation and differentiation ofmurine CD4 single-positive (SP) T cells, we compared the secondaryresponses of staphylococcal enterotoxin A (SEA)-induced neonatalthymic, adult thymic and adult splenic CD4 SP T cell blastsprepared from whole or heat-stable antigen^low CD4 SP T cells.Proliferative responses upon re-stimulation with SEA were strongin adult splenic CD4 SP T cell blasts, but quite weak in neonatalthymic and adult thymic CD4 SP T cell blasts. SEA-induced IL-2production was weaker in neonatal thymic blasts than in theadult splenic CD4 SP T cell blasts. In contrast, SEA-inducedIL-4 production was high in neonatal thymic CD4 SP T cell blasts,and low in adult splenic and thymic CD4 SP T cell blasts. Expressionof GATA-3, that directs production of IL-4 in T cells, examinedat protein and mRNA levels, was higher in neonatal thymic cellsthan in adult thymic and splenic cells. These results suggestthat neonatal and adult thymic CD4 SP T cells in the final stageof maturation are relatively immature compared with adult splenicCD4 SP T cells. The cytokine production profile of neonatalthymic CD4 SP T cells suggests that they are inclined towardsa T_h2 response.     

Analysis of recent thymic emigrants with subset- and maturity-related markers

The thymus plays an integral role in the development and production of T lymphocytes. However, thymocytes differ markedly in their phenotypic characteristics from the T cells normally found in the peripheral lymphoid organs. We have examined the phenotypic characteristics of recent thymic emigrants and compared them with both mature phenotype thymocytes (CD4+ CD8-CD3+ and CD4-CD8+ CD3+) and lymph node T cells. Recent thymic emigrants were defined as those fluorescein-positive cells found in the lymph node up to 16 h after intrathymic injection of fluorescein. Most cells emigrating from the thymus expressed CD3 and either CD4 or CD8, indicating maturity. Recent thymic emigrants, like mature phenotype thymocytes, were slightly larger on average than peripheral T cells, but this differential was lost within 24 h of emigration. Also like mature thymocytes but unlike peripheral T cells, some recent emigrants expressed heat-stable antigen. This did not change within 24 h of emigration. The antigen CD44 (Pgp-1, Ly-24) was expressed on a proportion of mature thymocytes, recent thymic emigrants, and peripheral T cells, and its expression did not show any clear relationship to maturity. The antigen CD45R also did not show marked changes associated with maturity, but our data do not parallel the published data of the expression of CD45R in the human. We conclude that recent thymic emigrants are phenotypically mature with respect to some antigens but not others. None of the antigens we investigated could have been used to uniquely distinguish recent thymic emigrants from peripheral T cells or from mature thymocytes.     

T cell receptor targeting to thymic cortical epithelial cells in vivo induces survival,activation and differentiation of immature thymocytes

We report that targeting of T cell receptors (TcR) to non-major histocompatibility complex (MHC) molecules on thymic cortical epithelial cells by hybrid antibodies in vivo and in fetal thymic organ cultures results in phenotypic and functional differentiation of thymocytes. A single pulse with hybrid antibodies rescues immature, CD4/8 double-positive thymocytes from their programmed death in vivo, induces expression of the early activation antigen CD69 followed by TcR up-regulation, concomitant down-regulation of CD8 or CD4 and their conversion to functional mature T cells by day 3. This temporal sequence of maturation only affects small thymocytes without co-induction of blastogenesis. TcR targeting to MHC class II-positive epithelial cells predominantly induces CD4-positive T cells. This generation of CD4 single-positive T cells occurs also in MHC class II-deficient mice and thus is independent of CD4-MHC class II interactions. Moreover, in the presence of a specific deleting antigen (Mls 1^a),TcR targeting results in transient activation of immature thymocytes, however, not in subsequent TcR (Vβ6) up-regulation and development of single-positive T cells. Our findings imply that TcR cross-linking to cortical epithelial cells is sufficient to confer a differentiation signal to immature thymocytes. Futhermore, this approach distinguishes two independent TcR-mediated intrathymic events: activation and subsequent deletion of the same thymocyte subset.     

The murine homolog of human Ep-CAM,a homotypic adhesion molecule,is expressed by thymocytes and thymic epithelial cells

In this report, we demonstrate that gp40, a molecule previously shown to be expressed by thymic epithelial cell lines in vitro and by thymic epithelial cells in vivo, is the murine homolog of human Ep-CAM, a calcium-independent homotypic adhesion molecule. gp40 is also expressed at low levels by thymocytes and peripheral T cells. In the adult thymus, gp40 expression was inversely related to the state of thymocyte maturation, with the highest levels associated with CD4^? CD8^? and CD4⁺CD8⁺ thymocyte populations. Ultrastructural immunohistochemistry revealed gp40 localization to areas of thymocyte/epithelial contact and demonstrated that gp40 is also expressed by thymic dendritic cells. During fetal development, thymocytes at days 14–16 of gestation expressed high levels of gp40. At later stages, the observed decline in the frequency of gp40⁺ cells and levels of expression correlated with the emergence of αβ⁺ thymocytes by day 18 of gestation. In short-term cultures, stimulation of unfractionated adult thymocytes with concanavalin A increased gp40 expression, particularly among CD3^hi and CD3^int thymocyte populations. This demonstration that Ep-CAM, initially considered to be expressed primarily by epithelial cells, is also expressed by thymocytes, T cells and antigen-presenting cells, raises the possibility that Ep-CAM may contribute to adhesive interactions between thymocytes and epithelial cells or dendritic cells, either in the context of thymocyte development or peripheral T cell trafficking and function.     

Expression of early activation antigen (CD69) during human thymic development.

The novel early activation antigen, EA1, has been shown to be induced by mitogens, antigens and the tumour promoter, phorbol myristate acetate (PMA), on human lymphocytes. This antigen has been designated to be CD69. EA1 has also been shown to be expressed on thymocytes without exogenous activation stimuli. In order to characterize further the expression of EA1 on thymocytes, the ontogeny of its expression was studied. EA1 appeared between 7 and 9.5 weeks of gestation, after colonization of the thymic rudiment with CD7+ T cell precursors, but before the onset of compartmentalization of the thymus into cortical and medullary zones. After cortico-medullary differentiation, the majority of medullary thymocytes expressed EA1 while only a fraction of the cortical thymocytes expressed this antigen. In the fetal and post-natal cortex, EA1 expression appeared to cluster in the subcapsular cortex. EA1+ cells were also scattered throughout the inner cortex. By two-colour fluorocytometric analysis of post-natal thymocytes, it was shown that EA1 was expressed on 30 to 65% of thymocytes. EA1 was expressed on CD4+ CD8+ as well as on the more immature CD4- CD8- thymocytes. In contrast to circulating T cells, thymocytes were much less responsive to PMA stimulation for the expression of EA1. Molecular characterization showed that EA1 on thymocytes had the same structure as that of activated peripheral T cells. In addition, thymic EA1 was constitutively phosphorylated. Thus, EA1 expression is acquired early during thymic development after colonization of the thymic rudiment by CD7+ T cell precursors. However, the specific role that EA1 may play in the activation and function of developing thymocytes remains to be determined.     

CD6: expression during development,apoptosis and selection of human and mouse thymocytes

CD6, a 130-kDa surface glycoprotein, is expressed primarily on cells of T lineage. A co-stimulatory role for CD6 in mature T cells has been shown, but the function of CD6 during thymocyte development is unknown. Since CD6 ligands are expressed on thymic epithelium, their interactions with CD6 could be important in thymic selection. In this report we show that CD6 is developmentally regulated in human and mouse thymocytes, and further demonstrate that increase in the level of CD6 expression correlates with expression of the selection marker CD69. We also show that activation via CD2 induces CD6 expression on mature human thymocytes and on a subset of immature human thymocytes that are resistant to apoptosis. In human and mouse thymocytes that express heterogeneous TCR, CD6 increases occur as double-positive thymocytes are selected to a single-positive stage. In contrast, in thymocytes from TCR transgenic mice, CD6 is barely increased following selection, suggesting that as functional avidity increases, requirements for CD6-dependent co-stimulation decrease. Taken together, these results indicate that during thymic development CD6-dependent signals may contribute both to thymocyte survival, and to the overall functional avidity of selection in both man and mouse.     

A potential role for CD69 in thymocyte emigration

The early activation marker, CD69, is transiently expressed on activated mature T cells and on thymocytes that are undergoing positive or negative selection in the thymus. CD69 is a member of the NK gene complex family of C-type lectin-like signaling receptors; however, its function is unknown. In this report, we describe the characterization of mice that constitutively express high levels of surface CD69 on immature and mature T cells throughout development. Constitutive surface expression of CD69 did not affect T cell maturation, signaling through the TCR or thymocyte selection. However, phenotypically and functionally mature thymocytes accumulated in the medulla of CD69 transgenic mice and failed to be exported from the thymus. The retention of mature thymocytes correlated with transgene dose and CD69 surface levels. These results identify a potential role for CD69 in controlling thymocyte export, and suggest that the transient expression of CD69 on thymocytes and T cells may function to regulate thymocyte and T cell trafficking.     

Immunomodulation of polypeptides fromChlamys farreri in vitro

Polypeptides fromChlamys Farreri(PCF) ,a wa-ter soluble octopeptide ,wasisolatedfromChlamysFarreribyenzyme engineering.The previous stud-iesin our laboratory showed that PCF was capableof protectingimmunocytesfromthe damages of Ul-traviolet or60Co,andthat PCFcouldresist the de-pression of lymphoproliferation caused by E2[1 ,2] .Based onthe earlier studies ,wefurtherinves-tigatedthe effects of PCF on immunityin vitrosoasto provide experimental basisforthe exploitationof PCF.MATERIAL…