PubMed Health⌕ Search

Biomedical subjects

K Huang

Publications and source records attributed to K Huang.

At least 163 records · Page 9Linked to original sources
PubMed1991

Thymic modulation of IL-2 and IL-4 synthesis by peripheral T cells.

In this paper we provide several lines of evidence to support the hypothesis that the thymus can exert regulatory influences on the functional capabilities of mature recirculating T cells. Our studies demonstrate that while the IL-2-producing potential of T cells that repopulate the secondary lymphoid organs of lethally irradiated and stem cell-reconstituted mice is significantly reduced compared to that of T cells harvested from normal mice, the amount of IL-4 produced by the T cells of these experimental animals is equivalent to, or greater than, the amount produced by T cells from control animals. In addition, we determined that the amount of biologically active IL-2 and IL-4 secreted by T cells harvested from lethally irradiated animals who reconstitute their hematopoietic and immune systems under the influence of nonirradiated thymic epithelial grafts is essentially identical to the amount produced by T cells harvested from nonirradiated control animals. Collectively, these findings suggest that: (1) the alterations observed in the lymphokine-producing potential of T cells harvested from lethally irradiated and stem cell-reconstituted mice is not due to a direct effect of ionizing radiation on the T lymphocytes themselves, and (2) the exposure of the epithelial cells of the thymus to ionizing radiation during marrow-ablative regimens abrogates or modifies a component of thymic function which can influence the lymphokine-secreting potential of recirculating T cells. Further evidence for thymic involvement in the regulation of lymphokine production by peripheral T cells comes from our finding of a post-thymectomy time-dependent reduction in the capacity of T cells from animals to produce IL-2. Coincident with this reduction, T cells harvested from peripheral lymphoid organs of thymectomized animals demonstrated an augmentation in their IL-4-producing capabilities. The finding that treatment of thymectomized animals with the androgen steroid hormone dehydroepiandrosterone reestablished a normal IL-2-producing potential by their T cells makes it unlikely that the reduced capacity to produce IL-2 was secondary to a loss in fresh thymic emigrants.

Animals↗
PubMed1991

Formation of C8-modified deoxyguanosine and C8-modified deoxyadenosine as major DNA adducts from 2-nitropyrene metabolism mediated by rat and mouse liver microsomes and cytosols.

2-Nitropyrene, the geometric isomer of the most studied nitropolycyclic aromatic hydrocarbon (nitro-PAH), 1-nitropyrene, is an environmental contaminant detected in ambient air and a potent direct-acting mutagen. Its metabolic activation leading to the formation of DNA adducts was studied. The activated metabolite, N-hydroxy-2-aminopyrene, was prepared and reacted with calf thymus DNA. Upon enzymatic hydrolysis of the DNA, the resulting nucleosides were separated by HPLC, and the adducts were characterized by mass and proton NMR spectral analysis. Both N-(deoxyguanosin-8-yl)-2-aminopyrene and N-(deoxyadenosin-8-yl)-2-aminopyrene, in a 5:2 ratio, were identified. These adducts were then utilized as standards to identify the DNA adducts formed from reaction of [3H]2-nitropyrene with DNA mediated by liver microsomes and cytosols of mouse and rat. In all cases, both adducts were formed. The quantities of the two adducts formed in each system were: mouse liver microsomes (11.3 pmol [3H]2-nitropyrene/mg DNA), rat liver microsomes (23), mouse liver cytosol (11.4) and rat liver cytosol (5.1). Thus, these adducts were formed in highest yield from rat liver microsomes and the lowest from rat liver cytosol. The deoxyguanosine/deoxyadenosine adduct ratio was higher from rat and mouse liver microsomes (7.8:9.2) than from rat and mouse liver cytosols (2.5:3.1). Our results represent the first direct demonstration of a C8-deoxyadenosine adduct being formed as a major product from the reaction of a nitro-PAH metabolite with DNA.

Animals↗
PubMed1991

A lymphocyte homing receptor (L-selectin) mediates the in vitro attachment of lymphocytes to myelinated tracts of the central nervous system.

Lymphocytes enter lymph nodes by first adhering to high endothelial venules, an adhesive event mediated by a lectinlike lymphocyte receptor (L-selectin). Previously, it was shown with an in vitro assay that lymphocytes preferentially adhere to myelin-rich regions in brain sections. Here, using a recombinant form of L-selectin as an immunohistochemical reagent, we demonstrate potential ligands for L-selectin in myelinated regions of the central but not the peripheral nervous system. Using several antibodies and phorbol ester downmodulation of the receptor, we establish that L-selectin on human lymphocytes has a primary involvement in lymphocyte adherence to the myelinated regions. On mouse lymphocytes, the contribution of L-selectin appears to be partial. These findings raise the possibility that leukocyte targeting to myelin-rich regions, via a L-selectin dependent mechanism, may be a factor in the pathogenesis of certain central nervous system demyelinating diseases.

Animals↗
PubMed1991

Crystallization and chemical modification of disulfide bond of calf chymosin.

In order to carry out protein engineering of chymosin, purification, crystallization and chemical modification of calf chymosin were undertaken. The resolution of iso-enzymes A,B and the degraded product, fraction C was improved and the period of purification was shortened by using fast protein liquid chromatograph (FPLC). Crystal of approximately cubic shape was obtained from 10 mg/ml purified chymosin B at 4 degrees C after successive dialysis against 1.4, 1.8 and 2.0 M NaCl in 0.1 M sodium phosphate buffer. One disulfide bond located on the surface of chymosin molecule was reduced by 0.72 mM dithiothreitol (DTT) at pH 6.3. The reduced disulfide bond was identified as Cys250-Cys283 by using the method of cyanogen bromide cleavage and peptide separation. The reduction of one disulfide bond resulted in the loss of about 25% activity. Carboxymethylated and mercurated derivatives exhibit the similar activity to that of the reduced enzyme suggesting that Cys250-Cys283 plays some role in keeping the conformation with full activity.

Animals↗
PubMed1990

Regulation of murine lymphokine production in vivo. III. The lymphoid tissue microenvironment exerts regulatory influences over T helper cell function.

We investigated the capacity of murine T lymphocytes, isolated from various lymphoid organs of normal or antigen-primed donors, to produce IL-2 or IL-4 after activation with anti-CD3 or specific antigen. Our results established that T cells resident within lymphoid organs being drained by nonmucosal tissue sites (e.g., axillary, inguinal, brachial lymph nodes, or spleen) produced IL-2 as the predominant T cell growth factor (TCGF) after activation. Conversely, activated T cells from lymphoid organs being drained by mucosal tissues (Peyer's patches, and cervical, periaortic, and parathymic lymph nodes) produced IL-4 as the major species of TCGF. Analysis of the lymphoid tissues obtained from adoptive recipients of antigen-primed lymphocytes provided by syngeneic donors provided evidence that direct influences were being exerted on T cells during their residence within defined lymphoid compartments. These lymphoid tissue influences appeared to be responsible for altering the potential of resident T cells to produce distinct species of TCGF. Steroid hormones, known transcriptional enhancers and repressors of specific cellular genes, were implicated in the controlling mechanisms over TCGF production. Glucocorticoids (GCs) were found to exert a systemic effect on all recirculating T cells, evidenced by a marked dominance in IL-4 production by T cells obtained from all lymphoid organs of GC-treated mice, or after a direct exposure of normal lymphoid cells to GCs in vitro before cellular activation with T cell mitogens. Further, the androgen steroid DHEA appeared to be responsible for providing an epigenetic influence to T cells trafficking through peripheral lymphoid organs. This steroid influence resulted in an enhanced potential for IL-2 secretion after activation. Anatomic compartmentalization of the DHEA-facilitated influence appears to be mediated by differential levels of DHEA-sulfatase in lymphoid tissues. DHEA-sulfatase is an enzyme capable of converting DHEA-sulfate (inactive) to the active hormone DHEA. We find very high activities of this enzyme isolated in murine macrophages. The implications of our findings to immunobiology are very great, and indicate that T cells, while clonally restricted for antigen peptide recognition, also appear to exhibit an extreme flexibility with regards to the species of lymphokines they produce after activation. Regulation of this highly conservative mechanism appears to be partially, if not exclusively, controlled by cellular influences being exerted by distinct species of steroid hormones, supplied in an endocrine or a paracrine manner where they mediate either systemic or tissue-localized influences, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Mechanisms of pertussis toxin inhibition of lymphocyte-HEV interactions. I. Analysis of lymphocyte homing receptor-mediated binding mechanisms.

The molecular mechanisms by which pertussis toxin (PTX) inhibits lymphocyte homing to peripheral lymph nodes (PLN) remain poorly understood. PTX-treated lymphocytes express homing receptors, yet cannot extravasate into PLN in vivo. Methylation of PTX, a procedure known to inactivate the B-oligomer of the toxin, restored high endothelial venule (HEV) binding capacity. In vitro studies established that toxin exposure inhibited the accessory role of LFA-1 in HEV binding. In contrast, PTX-exposed lymphocytes exhibited normal MEL-14-mediated HEV binding. Analysis of membrane fluidity revealed a 20% decrease in fluorescence polarization in PTX-exposed lymphocytes. On the basis of the current experiments, we propose a "zipper" model of lymphocyte-HEV interaction, in which lateral mobility of adhesion receptors in the cell membrane toward a site of endothelial contact is necessary to maintain adhesion against the shear force due to blood flow. PTX inhibits these processes by decreasing membrane fluidity, and by altering accessory adhesion molecule function.

Animals↗
PubMed1990

[The effects of needling acupoint, nonpain and pain stimulation on electroencephalogram (EEG) of somatosensory area analysed by computer].

The present study was to observe the change of EEG power spectrum during acupuncturing, nonpain stimulating and pain stimulating; then to comparatively analyse the effects of acupuncturing acupoint on brain function. The work was performed on 30 normal subjects. Nonpain or pain stimulation was applied to a medial finger, and the intensity of stimulation was determined by subject's report. Acupoints were "Neiguan" and "Jianshi". EEGs were recorded on a tape recorder before, during and after each stimulation. Then EEG power spectrum were analysed by SM-2100 computer. The results were as follows: According to the analysis of EEG power spectrum, in most of subjects, alpha (a) band was shifted to higher band during pain stimulating, there was significant change, P less than 0.05. The highness of a spike was significantly increased during acupuncturing acupoints, P less than 0.02. The ratio of delta power spectra to theta (theta) and delta (delta) power spectra showed increased tendency during acupuncturing or nonpain stimulating, but decreased during pain stimulating. It was indicated that nociceptive pain-stimulation resulted in hyposynchrony of EEG: frequency was increased, amplitude was decreased, alpha rhythm was inhibited to a certain extent; acupuncturing acupoints had the effect which could strengthen the stability of EEG rhythmic activities. We know that EEG rhythmic activities show clearly the stability of balance inside organism. So this result suggested that acupuncturing acupoint could play a role in modulating the balance inside organism and enhancing the stability of brain function.

Acupuncture Points↗
PubMed1989

Molecular mechanisms of lymphocyte extravasation. III. The loss of lymphocyte extravasation potential induced by pertussis toxin is not mediated via the activation of protein kinase C.

The present study evaluated whether protein kinase C (PKC) activation was involved in the lymphocytosis promoting properties of pertussis toxin (Ptx). The exposure of mouse lymphocytes to phorbol esters (as a means to selectively activate PKC) caused a depression in their subsequent capacity to localize into lymph nodes and Peyer's patches in vivo. This pattern of inhibition was quite similar to that observed with lymphocytes treated with Ptx. The mechanisms responsible for the observed decreases in localization to lymphoid organs caused by these two agents, however, appeared to be distinct. Exposure of lymphocytes to PMA was followed by a time and dosage-dependent decrease in the surface density of MEL-14 defined homing receptors. Ptx-treated lymphocytes retained normal density of this homing receptor. Consequently, PMA-treated lymphocytes lost their capacity to bind to high-endothelial venules in in vitro lymph node binding assays while Ptx-treated cells retained normal high-endothelial venule binding potential. We conclude from this study that: 1) the activation of PKC in lymphocytes by PMA can alter their recirculation properties via mechanisms that diminish their expression of surface receptors which support extravasation into lymph node and mucosal lymphoid tissues, and 2) even though Ptx has been reported to elevate the rate of inositol phosphate turnover in lymphocytes, the loss of extravasation potential of Ptx-treated lymphocytes is not mediated via the modification of surface homing receptors as observed in cells exposed to the known PKC activator, PMA.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗