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Y J Liu

Publications and source records attributed to Y J Liu.

At least 19 recordsLinked to original sources
PubMed1995

Human follicular dendritic cells enhance cytokine-dependent growth and differentiation of CD40-activated B cells.

Germinal centers constitute microanatomic subunits within secondary follicles where B cells undergo somatic mutations, isotype switch and affinity selection. This allows the generation of memory B cells and plasma cells, whose Igs bind to the eliciting Ag with a high affinity. T cells and follicular dendritic cells (FDCs) are thought to play key roles in the germinal center reaction. To study effects of FDCs on B cell growth and differentiation, we have isolated FDC-lymphocyte clusters from human tonsils by enzymatic digestion and centrifugation of the resulting cell suspension through BSA gradient. Irradiated FDC-lymphocyte clusters induced moderate proliferation of autologous B cells. IL-2 was the only cytokine able to enhance B cell proliferation cocultured with FDCs. When B cells were activated by soluble anti-CD40 Ab with or without IL-2, IL-3, IL-4, IL-10 or IL-13, addition of FDCs increased B cell proliferation. In the presence of FDCs, maximal B cell proliferation was observed in anti-CD40 stimulated cultures supplemented with either IL-4 + IL-10 or IL-2 + IL-10. Cultures performed in the presence of IL-2 and IL-10 resulted in high levels of Ig production in the presence of FDCs. In conclusion, the present study demonstrates that freshly isolated human FDCs can enhance the growth and differentiation of CD40-activated B cells.

B-Lymphocytes↗
PubMed1995

Generation of memory B cells and plasma cells in vitro.

After germinal center B cells undergo somatic mutation and antigen selection, they become either memory B cells or plasma cells, but the signal requirements that control entry into either pathway have been unclear. When purified human germinal center cells were cultured with interleukin-2, interleukin-10, and cells expressing CD40 ligand, cells with characteristics of memory B cells were generated. Removal of CD40 ligand from the system resulted in terminal differentiation of germinal center B cells into cells with the characteristics of plasma cells. These results indicate that CD40 ligand directs the differentiation of germinal center B cells toward memory B cells rather than toward plasma cells.

ADP-ribosyl Cyclase↗
PubMed1995

Glucose induces oscillations of cytoplasmic Ca2+, Sr2+ and Ba2+ in pancreatic beta-cells without participation of the thapsigargin-sensitive store.

Individual pancreatic beta -cells were used to study the glucose effects on the handling of Ca2+, Sr2+ and Ba2+. In extracellular medium containing one of these ions, single beta -cells responded to 11 mM glucose with large amplitude oscillations in cytoplasmic Ca2+, Sr2+ or Ba2+ with indistinguishable average frequencies (0.30-0.33/min). The oscillations disappeared after hyperpolarization with 400 microM diazoxide. Under such hyperpolarization, glucose stimulated the sequestration of Ca2+ and Sr2+ but not of repetitively mobilized by consecutive exposures to 100 microM carbachol. A 2-3 min exposure to 100 nM of the intracellular Ca(2+)-ATPase inhibitor thapsigargin also mobilized Ca2+ and Sr2+ and irreversibly abolished subsequent release by carbachol. However, thapsigargin did not prevent the large amplitude oscillations in Ca2+, Sr2+ or Ba2+ under non-hyperpolarizing conditions although the frequency of the Ca2+ oscillations was almost doubled. The results indicate that the slow oscillatory behavior of glucose-stimulated individual beta -cells does not depend on inositol 1,4,5-trisphosphate mediated release of intracellular Ca2+.

Animals↗
PubMed1995

Memory B cells from human tonsils colonize mucosal epithelium and directly present antigen to T cells by rapid up-regulation of B7-1 and B7-2.

Human memory B cells that carry mutated IgV region genes were isolated from tonsils by negative selection of IgD+ naive B cells and CD38+ germinal center B cells and plasma cells. They were mainly found within the intraepithelial areas, but not in the B cell follicles of human tonsils. Memory B cells but not naive B cells have the capacity to present antigen directly to T cells, owing to the constitutive expression of the accessory molecules B7-1/CD80 and B7-2/CD86. Signals through antigen receptors and CD40 antigen result in these two molecules being further up-regulated more rapidly and strongly on memory B cells than on naive B cells. The unique anatomical localization of memory B cells beneath the surface of mucosa, together with their strong APC capacity, may explain the well-known prompt and robust secondary antibody responses.

Antigen-Presenting Cells↗
PubMed1994

Molecular control of B lymphocyte growth and differentiation.

During antigen driven immune responses, antigen-specific naive B lymphocytes undergo a cascade of events including activation, expansion, mutations, isotype switch, selections and differentiation into either antibody secreting plasma cells or memory B cells. These antigen-dependent events, which we propose to call immunopoiesis, occur in different areas of secondary lymphoid organs, as well as other nonlymphoid organs. B cells interact with antigens and numerous cell types (T cells, dendritic cells, follicular dendritic cells and macrophages) through numerous cell surface molecules and cytokines. B cells costimulated through their antigen receptor and cytokines such as interleukin 2 (IL-2), IL-4 and IL-10 undergo limited proliferation and differentiation into immunoglobulin (Ig) secreting cells. In contrast, crosslinking of the B cell CD40 antigen, a member of the tumor necrosis factor (TNF) receptor family, results in major cellular activation further modulated by cytokines. In particular, IL-4 and IL-13 permit establishment of long-term factor-dependent B cell lines, as well as isotype switch towards the production of IgE and IgG4. Addition of IL-10 to CD40-activated B cells results in limited proliferation and remarkable differentiation into plasma cells. IL-10 also participates in isotype switch towards IgG1, IgG3 and IgA. The ligand for CD40, a member of the TNF family, is transiently expressed on activated T cells, and interrupted CD40/CD40-L interactions result in profoundly altered humoral immune responses.

Animals↗
PubMed1994

Interleukin 10 inhibits T cell alloreaction induced by human dendritic cells.

Human dendritic cells (DC) generated from CD34+ hematopoietic progenitors cultured in the presence of granulocyte macrophage colony stimulating factor (GM-CSF) and tumor necrosis factor (TNF)-alpha are related to Langerhans cells (DLC) and have been shown to induce a strong proliferation of allogeneic CD4+ T cells. The present study shows that recombinant human IL-10 (h-IL-10) inhibits the primary and secondary proliferative responses of both CD4+ and CD8+ T cells induced by allogeneic CD1a+ DLC. The alloreaction induced by DLC generated after 5-18 days of culture of CD34+ HPC was equally inhibited by h-IL-10, thus indicating that DLC were sensitive to h-IL-10 at all stages of differentiation. This is further indicated by the h-IL-10-induced inhibition of the T cell alloreaction mediated by interdigitating DC freshly isolated from tonsils. h-IL-10 specifically acted on DLC as it did not affect the proliferation induced by Epstein-Barr virus lymphoblastoid cell lines (EBV-LCL) nor that induced by immobilized anti-CD3. The inhibitory effect of h-IL-10 was not due to the production of suppressive factors by the DLC, as the addition of DLC and IL-10 did not inhibit EBV-LCL-induced T cell proliferation. Rather, the inhibition of cytokine production (IL-2, GM-CSF, TNF, IFN-gamma) observed after 24 h of co-culture may explain the inhibition of T cell DNA synthesis detected 3 days later. The h-IL-10-induced inhibition of human DC mediated alloreaction advocates considering the use of h-IL-10 in the prevention of transplant rejection and graft versus host disease, phenomena initiated by DC.

Antigen Presentation↗
PubMed1994

The CD40 antigen and its ligand.

CD40 is an integral membrane protein found on the surface of B lymphocytes, dendritic cells, follicular dendritic cells, hematopoietic progenitor cells, epithelial cells, and carcinomas. It is a 45-50 kDa glycoprotein of 277 aa, which is a member of the tumor necrosis factor receptor superfamily. The CD40 gene maps to human chromosome 20q11-2-q13-2. CD40 binds to a ligand (CD40-L) which is an approximately 35 kDa glycoprotein of 261 aa, a member of the tumor necrosis factor superfamily. The CD40-L gene maps to human chromosome Xq24. This CD40-L is expressed on activated T cells, mostly CD4+ but also some CD8+ as well as basophils/mast cells. The CD40-L is defective in the X-linked hyper-IgM syndrome. Cross-linking of CD40 with immobilized anti-CD40 or cells expressing CD40-L induces B cells to proliferate strongly, and addition of IL-4 or IL-13 allows the generation of factor-dependent long-term normal human B cell lines and the secretion of IgE following isotype switching. Addition of IL-10 results in very high immunoglobulin production with limited cell proliferation. IL-10 induces naive B cells to produce IgG3, IgG1, and IgA1, and further addition of TGF beta permits the secretion of IgA2. Several evidences suggest that CD40-dependent activation of B cells is important for the generation of memory B cells within the germinal centers: (i) CD40 activated germinal center B cells cultured in the presence of IL-4 acquire a memory B cell phenotype, (ii) CD40 activated B cells can undergo isotype switching, (iii) the deficit of CD40-L results in the hyper-IgM syndrome characterized by lack of germinal centers in secondary lymphoid organ follicles and lack of IgG, IgA, and IgE, and (iv) CD40-L positive T cells are present in secondary follicles. Thymic epithelial cells, activated monocytes, and dendritic cells express CD40 antigen which may be involved in an enhanced cytokine production by these cells, allowing an amplification of T cell proliferation. Finally, as other members of the tumor necrosis factor receptor family have been shown to bind several ligands, it is possible that CD40 may bind other ligands that may trigger CD40 on different cell types such as hematopoietic cells or epithelial cells.

Amino Acid Sequence↗
PubMed1994

Intracerebral co-grafting of Schwann's cells and fetal adrenal medulla in the treatment of Parkinson's disease.

Intracerebral co-grafting of Schwann's cells and human fetal adrenal medullary tissue was performed in 10 patients with Parkinson's disease. One to six months after grafting, symptoms were improved significantly for 1 to 3 grade. Among them, 2 patients resumed nearly normal daily activities. Long-term follow-up showed that the symptoms were not improved satisfactorily in some patients. It is considered that careful selection of patients, administration of amantadine, and co-grafting of Schwann's cells which prompts the survival of chromaffin cells are essential to better results.

Adrenal Medulla↗
PubMed1994

Vibration arthrometry of the knee with torn meniscus: a preliminary report.

Although projects using vibration signals generated by the joint to detect joint disorders are still experimental, vibration arthrometry has been shown to be useful in assessing meniscal pathology. A prospective study using vibration arthrometry to diagnose meniscal tears was carried out in 25 consecutive patients with knee injuries. They comprised 20 males and five females with an average age of 34 years. An arthroscopic examination of the injured knee was given to every patient. Six cases of medial meniscal tear, 12 lateral meniscal tear, and two torn discoid menisci were found. The remaining five cases had normal menisci. By correlating the vibration arthrography of the patients to their corresponding arthroscopic findings, 15 were found to be true-positive, five true-negative and five false-negative. There were no false-positive readings. The accuracy, sensitivity and specificity of the vibration arthrometry in diagnosing meniscal tear was 80%, 75% and 100%, respectively. Vibration arthrometry was shown to be a reliable, non-invasive diagnostic tool in diagnosing meniscal tear of the knee.

Adolescent↗
PubMed1993

Morphological and functional properties of TM preneoplastic mammary outgrowths.

The TM series of preneoplastic mammary outgrowth lines was derived from the transplantation of the FSK mammary cell lines into the cleared mammary fat pads of syngeneic female BALB/c mice. The tumor-producing capabilities of the 6 TM outgrowth lines varied from high (TM2, -4, -6) to low (TM9, -10) to nil (TM3). Outgrowth lines 2, 4, and 6 each segregated into sublines of high and low tumor potential. The majority of the outgrowth lines exhibited a moderate to dense alveolar hyperplasia typical of mouse mammary hyperplasias. The exceptions to this picture were lines TM2H and TM10 which exhibited a unique ductular morphology. The ductular morphology was not correlated with tumor potential of the outgrowth lines but was correlated with the expression of K6 and K14 keratins in luminal epithelial cells. In an examination of the growth and hormonal responsiveness properties of the TM outgrowth lines, the TM3 line stands as distinct from the other lines and from any other lines previously characterized in BALB/c mice. The TM3 line grew very slowly and failed to fill the fat pad by 12 months of age. At 12 months of age, the alveolar hyperplasia had regressed so that only bare ducts were present. The TM3 outgrowth was ovarian hormone dependent for growth and alveolar differentiation. TM3 outgrowth represents a minimally deviated mammary hyperplasia which has acquired the immortal phenotype but not the other phenotypic characteristics of mammary preneoplasias. This outgrowth line will be useful for examining the essential molecular changes important for the preneoplastic state, some of which are reported in an accompanying paper (D. Medina et al., Cancer Res., 53: 668-674, 1993).

Animals↗
PubMed1993

Immunophenotypic properties and estrogen dependency of budding cell structures in the developing mouse mammary gland.

The initial phase of growth of the parenchymal component of the mouse mammary gland is ductal clongation, which is mainly accomplished by proliferating cells in a specialized structure termed end bud. End buds are composed of multiple layers of epithelial cells (so called body cells) which are capped by a single layer of morphologically unique cells termed cap cells. We sought to examine the interrelationship between cap cells and other epithelial cell subclasses using a variety of antibodies to different keratin proteins and also antibodies to vimentin, actin and collagen IV. An extensive immunohistochemical characterization of the epithelial components of the developing and differentiating mammary gland demonstrated that cap cells were devoid of any immunohistochemically-detectable keratins but were positive for collagen IV. In contrast, the majority of cells in the end bud along with the luminal epithelial and myoepithelial cells were keratin positive. The body cells of the end bud were the only cells which were positive for antibody to keratin 6, a keratin which previously has been reported to be expressed in proliferating mammary epithelial cells. In addition, estrogen receptor was localized only to epithelial cells of ducts, alvcoli and body cells of end buds, but not to cap cells or myoepithelial cells. We interpret these results to suggest that cap cells are not totpotent stem cells but rather cells specialized in paving the way for ductal elongation as well as serving as precursors to myoepithelial cells.

Actins↗
PubMed1992

Effect of extracellular calcium concentration on angiotensin AT1 receptor-mediated smooth muscle contraction and antagonism in rabbit aorta.

Angiotensin-II (AII) stimulates smooth muscle contraction by activating angiotensin AT1 receptor which induces intracellular Ca2+ release and Ca2+ influx from extracellular space. In this study, effect of extracellular Ca2+ concentration ([Ca2+]0) on angiotensin AT1 receptor-mediated contractile response to AII has been examined in the absence and presence of [Sar1,Ala8]AII in rabbit aorta. A decrease in agonist potency and an increase in antagonist potency for depression were observed in low [Ca2+]0. Data were interpreted by applying an explanatory model developed previously. The result indicates that [Ca2+]0 is linked to the efficacy expression of AII at angiotensin AT1 receptor and this prompted speculation about the underlying mechanism.

Angiotensin II↗
PubMed1992

Germinal centres in T-cell-dependent antibody responses.

For more than a century follicles have been recognized as a site of intense cell proliferation and cell death. At last the significance of this activity is beginning to emerge: antigen-driven B-cell proliferation, somatic mutation, positive and negative selection, and memory and plasma cell development all appear to take place within the follicle.

Animals↗