Active-site mutations of diphtheria toxin: role of tyrosine-65 in NAD binding and ADP-ribosylation

Previous studies have suggested that tyrosine-65 (Tyr-65) of diphtheria toxin (DT) is located at the active site. To investigate the role of Tyr-65 in NAD binding and the ADP-ribosylation of elongation factor-2 (EF-2), we changed this residue to alanine and phenylalanine by site-directed mutagenesis of a synthetic gene encoding the catalytic fragment of DT (DTA). The alanine mutant was greatly diminished in ADP-ribosylation activity (350-fold) and NAD-glycohydrolase activity (88-fold), whereas the phenylalanine mutant was reduced in these activities only slightly. Dissociation constants (Kd) for NAD binding were 15 microM for wild-type DTA, 26 microM for the phenylalanine mutant, and greater than 800 microM NAD for the alanine mutant. However, both mutant enzymes were found to bind adenosine with nearly equal affinity as wild-type DTA. These results support a model of ADP-ribosylation in which the phenolic ring of Tyr-65 interacts with the nicotinamide ring of NAD, orienting the N-glycosidic bond of NAD for attack by the incoming nucleophile in a direct displacement mechanism.

Role of TCR zeta chain in T cell development and selection

Signals mediated by the T cell receptor (TCR) are required for thymocyte maturation and selection. To examine the role of TCR zeta chain signals in development, TCR expression was restored in zeta-deficient mice with transgenic zeta chains that partially or completely lacked sequences required for signal transduction. The zeta chain played a role in thymic development by promoting TCR surface expression, but zeta-mediated signals were not essential because TCRs that contained signaling-deficient zeta chains promoted T cell maturation and transduced signals associated with thymic selection.

Dipeptidyl peptidase IV from porcine seminal plasma: purification, characterization, and N-terminal amino acid sequence

Dipeptidyl peptidase IV (DPP IV) was purified to homogeneity from porcine seminal plasma by polyacrylamide gel electrophoresis (PAGE). The molecular weight of the purified enzyme was calculated to be approximately 290,000 on PAGE in the absence of sodium dodecyl sulfate (SDS) and 310,000 on Sephacryl S-300 HR column chromatography, and to be 115,000 and 105,000 on SDS-PAGE in the absence and presence of beta-mercaptoethanol. The enzyme is suggested to be composed of three identical subunits. The enzyme rapidly hydrolyzed the substrate Gly-Pro-MCA, and weakly the substrate Lys-Ala-MCA. It was strongly inhibited by diisopropylphosphofluoridate (DFP), and moderately by both phenylmethyl-sulfonyl fluoride (PMSF) and 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF). It was also strongly inhibited by zinc ion. The amino acid sequence of the first 18 residues of the enzyme was Asn-Lys-Gly-Thr-Asp-Asp-Ala-Ala-Ala-Asp-Ser-Arg-Arg- Thr-Tyr-Thr-Leu-Thr-. This sequence was highly homologous to the sequences in the rear of the transmembrane site of human and rat liver DPP IVs and mouse thymus DPP IV. The native DPP IV is suggested to be released into the seminal plasma after the cleavage of the hydrophobic N-terminal domain by chymotrypsin-like or pepsin-like enzymes. Other properties of DPP IV including kinetic parameters, pH stability and heat stability were characterized.

Selenium-containing peroxidases of germinating barley

Germinating barley grown on an artificial medium was exposed to 75Se-selenite for 8 d. Then the leaves were homogenized and proteins were separated by means of Sephadex G-150 filtration, followed by DEAE-Sepharose chromatography. Each fraction collected was assayed for total protein, radioactivity, and peroxidase activity. In barley leaves, three protein peaks (peaks no. I, II, and III) with peroxidase activity could be separated by Sephadex G 150 filtration. Each fraction was then further separated on DEAE-Sepharose chromatography. Thus, peaks I and II were resolved by DEAE-Sepharose into one major and two minor peaks of radioactivity. However, only the major peak showed peroxidase activity. Peak III was resolved from the gel filtration on the DEAE-sepharose into one major and four minor peaks of radioactivity. The major and three of the minor radioactivity peaks contained peroxidase activity. The protein fractions were separated by polyacrylamide gel electrophoresis. The molecular weights of separated proteins were estimated by means of molecular markers, and 75Se radioactivity was evaluated by autoradiography. Thus, gel filtration peak I contained four bands with mol wts of 128, 116, 100, and 89 kDa. Of these, the 89 kDa protein contained selenium. Peak II contained three protein bands with mol wts 79.4, 59.6, and 59.9. The 59.6 band was a selenoprotein. Peak III contained four protein bands (and some very weak bands). The four major bands had mol wts of 38.6, 31.6, 30.2, and 29.2 kDa. The last mentioned band was a selenoprotein.

The uptake of Na-selenite in rat brain. Localization of new glutathione peroxidases in the rat brain

Polyunsaturated fatty acids (PUFAs) occur in phospholipids of synapses of central nervous system (CNS). PUFAs may thus determine the fluidity of synaptosomal membranes and regulate neuronal transmission. It was therefore tempting to suggest an oxidative system in CNS protecting the membrane function, e.g., glutathione peroxidase (GSH-Px). In order to trace GSH-Px Wistar rats were loaded with 4800 kBq of 75Se sodium selenite. By means of gradient ultracentrifugation, particulate fractions of CNS were isolated and radioactivity as well as selenium dependent GSH-Px were estimated. The following data were obtained: 1. All fractions (myelin, synaptic vesicles, synaptosomes, mitochondria, and microsomes) contained 75Se. 2. After acetone precipitation of GSH-Px activity, fractionation on Sephadex G-150 revealed in all particulate fractions at least two peaks of radioactivity with GSH-Px activity. 3. The two GSH-Px peaks from the Sephadex filtration were freeze dried and applied on a hydrophobic T-gel column and eluted with decreasing molarity of ammonium sulfate from 1.5 to 0.05M. The first Sephadex peak with GSH-Px activity from myelin and the second peak with GSH-Px activity from synaptic vesicles could now be resolved into two different fractions of radioactivity on the T-gel. The remaining Sephadex G-150 peaks could only be resolved into one peak of radioactivity. 4. SDS-polyacrylamide gel electrophoresis of the T-gel peaks from all fractions showed a protein band with a mobility identical with that of human erythrocyte GSH-Px. The T-gel elution of myelin, synaptic vesicles and mitochondria gave rise to nearly pure CNS GSH-Px activity. The data presented support the idea that CNS fractions have membrane bound GSH-Px activity that may function as protecting enzymes towards oxidative stress in the brain.

Holographic technique for three-dimensional three-component particle fields

We present the preliminary results of a new technique that permits three-dimensional three-component detection of displacing particle fields from a single observation direction. The technique utilizes time-sequence images independently reconstructed by dual-reference-beam off-axis holography. The image sections are then statistically correlated for displacement extraction, without the need for specific focusing.

Myelin localization of a central nervous system ligand for L-selectin

L-selectin is a lectin-like receptor involved in lymphocyte attachment to lymph node high endothelial venules (HEV). Previously, we showed that L-selectin also participates in the in vitro attachment of lymphocytes to central nervous system (CNS) white matter. Use of an L-selectin chimera demonstrated ligand sites within CNS white matter but not the peripheral nervous system (PNS). Now employing higher resolution mapping, including EM cytochemistry, we localize the ligands to the actual myelin sheaths of CNS neurons. In the shiverer mouse, which lacks compact myelin, ligands are greatly diminished. Comparison of the myelin-associated ligand with the previously characterized HEV-ligands demonstrates a number of differences.

The molecular structure of the complex of Ascaris chymotrypsin/elastase inhibitor with porcine elastase

BACKGROUND

The intestinal parasitic worm, Ascaris suum, produces a variety of protein inhibitors that defend the organism against the host's proteinases. Eight different proteins from Ascaris suum have been identified as inhibitors of serine proteinases, targeting chymotrypsin, elastase and trypsin. These inhibitors share 30-40% sequence identity with one another, but have virtually no sequence identity with members of any of the other families of serine proteinase inhibitors.

RESULTS

The crystal structure of the complex of porcine pancreatic elastase with a chymotrypsin/elastase inhibitor from Ascaris suum (the C/E-1 inhibitor) has been solved to 2.4 A resolution by the molecular replacement method. The C/E-1 inhibitor exhibits a novel folding motif. There are only two small beta-sheets and two single-turn 3(10)-helices in this inhibitor. Unlike the majority of proteins, the C/E-1 inhibitor does not have a hydrophobic core. The presence and unique topography of the five disulfide bridges suggests that they play important roles in maintaining the tertiary structure of the inhibitor. In addition, the side chains of several charged residues from electrostatic and hydrogen-bonding cascades, which also probably compensate for the lack of extensive secondary structures and a hydrophobic core. The reactive-site loop of this inhibitor displays a conformation that is characteristic of most serine proteinase inhibitors.

CONCLUSIONS

The structure of the C/E-1 inhibitor confirms that inhibitors from Ascaris suum belong to a novel family of proteinase inhibitors. It also provides conclusive evidence for the correct disulfide bridge connections. The C/E-1 inhibitor probably acts by a common inhibitory mechanism proposed for other substrate-like protein inhibitors of serine proteinases. The unusual molecular scaffolding presents a challenge to current folding algorithms. Proteins like the C/E-1 inhibitor may provide a valuable model system to study how the primary sequence of a protein dictates its three-dimensional structure.

Active-site mutations of the diphtheria toxin catalytic domain: role of histidine-21 in nicotinamide adenine dinucleotide binding and ADP-ribosylation of elongation factor 2

Diphtheria toxin (DT) has been studied as a model for understanding active-site structure and function in the ADP-ribosyltransferases. Earlier evidence suggested that histidine-21 of DT is important for the ADP-ribosylation of eukaryotic elongation factor 2 (EF-2). We have generated substitutions of this residue by cassette mutagenesis of a synthetic gene encoding the catalytic A fragment (DTA) of DT, and have characterized purified mutant forms of this domain. Changing histidine-21 to alanine, aspartic acid, leucine, glutamine, or arginine diminished ADP-ribosylation activity by 70-fold or greater. In contrast, asparagine proved to be a functionally conservative substitution, which reduced ADP-ribosylation activity by < 3-fold. The asparagine mutant was approximately 50-fold-attenuated in NAD glycohydrolase activity, however. Dissociation constants (Kd) for NAD binding, determined by quenching of the intrinsic protein fluorescence, were 15 microM for wild-type DTA, 160 microM for the asparagine mutant, and greater than 500 microM NAD for the alanine, leucine, glutamine, and arginine mutants. These and previous results support a model of the ADP-ribosylation of EF-2 in which histidine-21 serves primarily a hydrogen-bonding function. We propose that the pi-imidazole nitrogen of His-21 hydrogen-bonds to the nicotinamide carboxamide, orienting the N-glycosidic bond of NAD for attack by the incoming nucleophile in a direct displacement mechanism, and then stabilizing the transition-state intermediate of this reaction.

A recombinant amino-terminal fragment of bactericidal/permeability increasing protein (rBPI23) inhibits soluble CD14-mediated lipopolysaccharide-induced endothelial adherence for human neutrophils

Exposure of cultured human umbilical vein endothelial cells (HUVEC) to lipopolysaccharide (LPS) or interleukin 1 (IL-1) causes increased expression of adhesion molecules such as E-selectin and CD54 by HUVEC and consequently increased adherence of peripheral blood neutrophils. A recombinant aminoterminal fragment of bactericidal/permeability increasing protein (rBPI23) was shown to specifically block the LPS-induced adhesiveness of HUVEC for neutrophils. rBPI23 also prevented the LPS- but not IL-1 beta-induced upregulation on HUVEC of E-selectin and CD54. Furthermore, this inhibition was evident even when the endothelial cells were exposed to LPS for up to 1-2 h prior to rBPI23 addition. The inhibitory effects of an anti-CD14 monoclonal antibodies (mAb) were similar to those of rBPI23. Combination of the anti-CD14 mAb and rBPI23 resulted inhibition greater than either one used alone. These studies demonstrate that rBPI23 acts as a specific and potent inhibitor of soluble CD14-mediated LPS induction.

Interference by complex structures of target DNA with specific PCR amplification

It has been considered that target DNA is a forgiving component for PCR amplification. Herein we present evidence to demonstrate that secondary structure located at the end of a template may interfere with the specificity of amplification. Experiments indicate that nonspecific amplification results from a long stretch of stem and loop structures at the 3' end of prochymosin cDNA. Based on the sequence of mRNA coding for prochymosin, it is argued that the sequence responsible for the formation of the complex structure described here is most likely generated during synthesis of the second cDNA strand.

Functional implication of disulfide bond, Cys250 -Cys283, in bovine chymosin

The reduction, carboxymethylation and mercuration of disulfide bond, Cys250-Cys283, located on the surface of bovine chymosin molecule resulted in the loss of about 25% of enzyme activity, suggesting that Cys250-Cys283 is not intimately involved in catalytic mechanism. Cys250 and Cys283 were substituted with Asp. and Ser. by site- directed mutagenesis of the structural gene coding for bovine prochymosin B. All three mutants (C250D/C283S, C250D, C283S) failed to be activated to chymosin in acid, indicating that Cys250-Cys283 might have some contribution to the correct refolding of the unfolded prochymosin.

Crystallization and preliminary X-ray diffraction studies of two mutants of lactate dehydrogenase from Bacillus stearothermophilus

Bacillus stearothermophilus lactate dehydrogenase, one of the most thermostable bacterial enzymes known, has had its three-dimensional structure solved, the gene coding for it has been cloned, and the protein can be readily overexpressed. Two mutants of the enzyme have been prepared. In one, Arg171 was changed to Trp (R171W) and Gln102 was changed to Arg (Q102R). In the other, the mutation Q102R was maintained, but Arg171 was changed to Tyr (R171Y). In addition, an inadvertent C97G mutant was present. Both mutants have been crystallized by the hanging drop vapor diffusion method at room temperature. Bipyrimidal crystals have been obtained against (NH4)2SO4 in 50 mM piperazine HCl buffer. The crystals belong to space group P6(2)22 (P6(4)22) (whereas the native enzyme, the structure of which has been solved by Piontek et al., Proteins 7:74-92, 1990) crystallized in the space group P6(1)) with a = 102.3 A, c = 168.6 A for the R171W, Q102R, C97G triple mutant, and a = 98.2 A; c = 162.1 A for the R171Y, Q102R, C97G mutant. These crystal forms appear to contain one-quarter of a tetramer (M(r) 135,000) in the asymmetric unit and have VM values of 3.8 and 3.3 A3/dalton, respectively). The R171W mutant diffracts to 2.5 A and the R171 Y mutant to approximately 3.5 A.

[A systematic study on comprehensive utilization of fibers of radix Ophiopogonis]

The components, toxicology, bioactivity and application of fibers of Radix Ophiopogonis (RO) were studied. The components of its fibers and roots are similar. In a clinical study with 100 aged patients, the aging syndromes were markedly improved. No side-effect was found.

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.

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.

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.

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.

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)

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.

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.

Characterization of two monoclonal antibodies that recognize high molecular weight colon antigens

Two monoclonal antibodies, M32-1 (Ig-G1,k) and M39-2 (IgM,k), were prepared against high molecular weight (greater than 650 kDa) cytosol antigens (HMW-CA) of a human adenocarcinoma of the colon (GW-39). These monoclonal antibodies appeared to bind to determinants on two distinct high molecular weight colon antigens. One was shown by gel filtration to be a 650 kDa glycoprotein (gp650) containing at least one 300 kDa antigenic subunit (gp300). The other antigen eluted from a S-300 Sephacryl column at a molecular size of 600 kDa (gp600) and was resistant to dissociation by detergents, salts and chaotropic agents. The differential sensitivity of these two high molecular weight glycoproteins to treatment with trypsin, chondroitinase ABC, HNO2, endoglycosidase H and 2-mercaptoethanol suggest that monoclonal antibodies M39-1 and M39-2 react with distinct antigenic determinants located on two separate, high molecular weight, colon antigens. Since these antigens are only detected in extracts prepared from normal mucosa, well-differentiated tumors or margins of well-differentiated tumors, their expression appears to be related to a well-differentiated cell phenotype.

Effect of ionizing radiation on thymic epithelial cell function. I. Radiation-spared thymic epithelial grafts expedite the recovery of T cell function in lethally irradiated and fetal liver reconstituted mice

A murine model system was developed to determine whether ionizing radiation has a detrimental influence on thymic epithelium, cell function. Normal mice were lethally irradiated, grafted intracamerally with normal fetal thymic epithelium, and then reconstituted with fetal liver cells. These animals were compared with a group of animals who received their thymic grafts before the irradiation protocol. Analysis of the reconstitution of T cell function in peripheral lymph nodes and spleens at various times post transplantation demonstrated that animals with radiation-spared thymic grafts had superior proliferative responses to T cell mitogens and alloantigens. It was also determined that the capacity of these animals to elicit contact hypersensitivity responses was significantly greater when compared with animals whose thymic grafts had been radiated. The observed difference in T cell function could not be ascribed to a difference in the rate of export of mature T cells from the thymic grafts since the absolute number of Thy-1+, L3T4+, or Lyt-2+ lymphocytes present in the peripheral lymphoid compartment of our two groups of animals was equivalent. Immunohistologic analysis of the thymic grafts demonstrated a marked reduction in the medullary compartment of the repopulated grafts that had been exposed to ionizing radiation. The results of this study suggest: 1) that irradiation of the thymic microenvironment during marrow ablative preparative regimens may be in part responsible for some of the immune alterations observed in marrow transplant recipients, and 2) that our model system may provide a valuable tool for delineating the roles played by medullary and cortical epithelial cells of the thymus on the T cell maturation and education processes.

Effect of ionizing radiation on thymic epithelial cell function. I. Radiation-spared thymic epithelial grafts expedite the recovery of T cell function in lethally irradiated and fetal liver reconstituted mice

A murine model system was developed to determine whether ionizing radiation has a detrimental influence on thymic epithelium, cell function. Normal mice were lethally irradiated, grafted intracamerally with normal fetal thymic epithelium, and then reconstituted with fetal liver cells. These animals were compared with a group of animals who received their thymic grafts before the irradiation protocol. Analysis of the reconstitution of T cell function in peripheral lymph nodes and spleens at various times post transplantation demonstrated that animals with radiation-spared thymic grafts had superior proliferative responses to T cell mitogens and alloantigens. It was also determined that the capacity of these animals to elicit contact hypersensitivity responses was significantly greater when compared with animals whose thymic grafts had been radiated. The observed difference in T cell function could not be ascribed to a difference in the rate of export of mature T cells from the thymic grafts since the absolute number of Thy-1+, L3T4+, or Lyt-2+ lymphocytes present in the peripheral lymphoid compartment of our two groups of animals was equivalent. Immunohistologic analysis of the thymic grafts demonstrated a marked reduction in the medullary compartment of the repopulated grafts that had been exposed to ionizing radiation. The results of this study suggest: 1) that irradiation of the thymic microenvironment during marrow ablative preparative regimens may be in part responsible for some of the immune alterations observed in marrow transplant recipients, and 2) that our model system may provide a valuable tool for delineating the roles played by medullary and cortical epithelial cells of the thymus on the T cell maturation and education processes.