Intracellular distribution of actin in cells of the organ of Corti: a structural basis for cell shape and motility

Immunofluorescence staining and phalloidin labeling have provided localization of actin in the sensory and supporting cells of the inner ear at the light microscopic level. However, with electron microscopy, neither actin nor actin filaments have been found in the outer hair cell body. This paper describes various techniques utilized to preserve and identify cytoplasmic actin at the ultrastructural level. Post-embedding staining of Lowicryl K4M sections, pre-embedding staining of permeabilized cells of the organ of Corti, pre-embedding staining of vibratome sections, and pre-embedding staining of permeabilized dissociated cells documented the presence of actin, but each of these techniques was best suited to localize actin in specific parts of the cell. Cytoplasmic actin was labeled when isolated cells were lightly fixed and membranes were permeabilized with detergent--conditions under which the cell ultrastructure was compromised. Under conditions of optimal fixation, cytoplasmic filaments embedded in the dense granular matrix of the hair cell cytoplasm were observed.

Myxoid meningioma

A mucosubstance-rich myxoid meningioma that recurred twice is reported. This rare form of meningioma is a potential source of confusion with other myxoid neoplasms such as metastatic adenocarcinoma or chordoma. In addition to the usual stigmata of meningial cell differentiation, ultrastructural examination revealed spaces delineated by a network of cellular processes and enclosing loose granular and fibrillar material. This neoplasm is probably linked to the so-called microcystic meningioma but has an overt production of acid mucosubstance.

Continuous fluorimetric assessment of the changes in cytoplasmic calcium concentration during exposure of rat isolated myocardium to conditions of simulated ischaemia

1. The cytoplasmic calcium concentration ([Ca]c) of rat isolated atrial myocardium was assessed with the dye indo-1. Dye-loaded atria were superfused with physiological salt solution and excited with radiation at 360 nm, while epifluorescence emissions were collected simultaneously at 400 nm and 500 nm. The ratio of these emissions was used as a measure of [Ca]c. 2. Dye-loaded atria showed a phasic rise and fall in [Ca]c with each applied electrical pacing stimulus. The amplitudes of systolic increments in tension and [Ca]c were augmented by the presence of isoprenaline. 3. Atria superfused with a solution the composition of which resembled that found extracellularly in regions of ischaemia rapidly lost systolic increments in tension and [Ca]c, while end-diastolic [Ca]c and tension gradually rose. 4. The presence of lactate (20 mM) or flufenamate (5 microM) in the superfusate during simulated ischaemia aggravated the rises in both end-diastolic tension and end-diastolic [Ca]c. Inclusion in the superfusate of sulphinpyrazone (50 microM) or glucose (20 mM) protected against some of the deleterious effects of lactate seen during simulated ischaemia.

Simultaneous production of interleukin 2, interleukin 4 and interferon-gamma by activated human blood lymphocytes

The production of interleukin 2 (IL 2), IL 4 and interferon-gamma (IFN-gamma) by in vitro activated unselected human blood mononuclear cells was studied at a single-cell level. Individual lymphokine-synthesizing cells were identified by intracellular immunofluorescent staining using cytokine-specific monoclonal or polyclonal antibodies. Cultures from adult blood donors revealed a biphasic kinetic production pattern for IL 2 and IFN-gamma with peaks occurring 4-6 and 24-30 h after initiation of the cultures. Approximately 20%-40% of the lymphocytes produced IL 2 and IFN-gamma. In contrast, only 1%-3% of the lymphocytes synthesized IL 4 with maximal frequency after 6 h of culture. CD4+ as well as CD8+ T cells contributed to the synthesis of all three lymphokines studied. CD4+CD45R- T cells were the major producers of IL 2 and IL 4, while CD8+CD45R- T cells were the most common phenotype of IFN-gamma-synthesizing cells. By performing two-color immunofluorescence studies we observed that among IL 4-producing cells every second one made simultaneously IL 2 and every fourth one made IFN-gamma. Mononuclear cells from umbilical cord blood could be stimulated to make IL 2 to the same extent as cells from adult blood donors. No IL 4 production and a strikingly reduced frequency of IFN-gamma producers were noted in cell cultures from neonates. IL 2, IL 4 and IFN-gamma accumulated in the Golgi system, which resulted in a characteristic morphology of the staining, eliminating problems with evaluation of background signals.

Ca2+ binding capacity of cytoplasmic proteins from rod photoreceptors is mainly due to arrestin

Arrestin (also called S-antigen or 48-kDa protein) binds to photoexcited and phosphorylated rhodopsin and, thereby, blocks competitively the activation of transducin. Using Ca2+ titration in the presence of the indicator arsenazo III and 45Ca2+ autoradiography, we show that arrestin is a Ca2(+)-binding protein. The Ca2+ binding capacity of arresting-containing protein extracts from bovine rod outer segments is about twice as high as that of arrestin-depleted extracts. The difference in the Ca2+ binding of arrestin-containing and arrestin-depleted protein extracts was attributed to arrestin. Both, these difference-measurements of protein extracts and the measurements of purified arrestin yield dissociation constants for the Ca2+ binding of arrestin between 2 and 4 microM. The titration curves are consistent with a molar ratio of one Ca2+ binding site per arrestin. No Ca2+ binding in the micromolar range was found in extracts containing mainly transducin and cGMP-phosphodiesterase. Since arrestin is one of the most abundant proteins in rod photoreceptors occurring presumably up to millimolar concentrations in rod outer segments, we suggest that aside from its function to prevent the activation of transducin, arrestin acts probably as an intracellular Ca2+ buffer.

Characterization of site-specific polyclonal antibodies to c-erbA peptides recognizing human thyroid hormone receptors alpha 1, alpha 2, and beta and native 3,5,3'-triiodothyronine receptor, and study of tissue distribution of the antigen

The translated products of v-erbA-related cDNAs have been demonstrated to be thyroid hormone receptors, and three different forms of receptor (alpha 1, alpha 2, and beta) have been found in human tissues. We synthesized five peptides corresponding to different portions of these three receptors and raised site-specific polyclonal-antipeptide sera in rabbits. Each antibody displayed high titer and specificity for its respective antigen when tested in an enzyme-linked immunosorbent assay. Each immunoprecipitated the corresponding in vitro translated products of human c-erbA alpha 1, alpha 2, or beta. Two of the antisera were specific for beta, one for alpha 2, and one detected a sequence common to alpha 1 and alpha 2. The fifth was directed toward the DNA-binding area of the proteins and interacted with each receptor. The four antibodies against alpha 1 and beta immunoprecipitated the native thyroid hormone receptor from rat liver and caused a partial shift in the elution profile of the native receptor labeled with [125I]T3 on Sephacryl S-300 column chromatography. The antibody against alpha 2 protein did not interact with native thyroid hormone receptor from rat liver. Using the indirect immunofluorescence technique with the five antibodies, we detected immunoreactivity primarily in the nucleus of cells in several tissues. In general, there was coordinate expression of both alpha and beta receptors in each organ examined, in agreement with previous data on tissue distribution of mRNAs for human thyroid hormone receptors. These studies prove the identity of v-erbA-related gene products with native thyroid hormone receptors and the expression of both alpha and beta receptors in nuclei of human and rat tissues.

Colloidal gold labeling of intracellular ligands in dorsal root sensory neurons, visualized by scanning electron microscopy

We report a novel technique that combines high-resolution scanning electron microscopy (SEM) of intracellular structures with backscattered electron imaging (BEI) of colloidal gold-labeled intracellular ligands. Murine dorsal root ganglia were immersion-fixed, freeze-cleaved, labeled with gold complexes, and critical point-dried. Specimens were carbon-coated and viewed by BEI. They were then minimally sputter-coated with gold and previously identified cells relocated by secondary electron imaging (SEI). This permitted increased resolution of intracellular detail while gold particles remained detectable by BEI. Incubation with RNAse-gold and DNAse-gold complexes resulted in specific labeling of cytoplasm and nucleus, respectively. Immunolabeling of neurofilament (NF) and small nuclear ribonucleoproteins (snRNP) resulted in selective labeling of intracellular antigens. Nonspecific binding was abolished by use of 1% skin milk. Specifically, incubation with monoclonal anti-NF68 resulted in labeling of cytoplasm in 66% of neurons, notably of the large cells known to contain large amounts of NF. Satellite cells, which lack NF, showed low levels of background label. Human autoimmune anti-Sm serum recognizes snRNP particles, with the exception of the nucleolar U3 snRNP. Labeling with this serum resulted in specific labeling of 92% of nuclei, with only background labeling over nucleoli and cytoplasm. The results show that it is feasible to employ high-resolution SEM in conjunction with colloidal gold labeling to localize intracellular ligands in situ.

Acridine orange--RNA histofluorescence of sarcomas and small round cell tumors of childhood

Forty-nine pediatric malignant neoplasms were stained with acridine orange (AO) fluorochrome to qualitatively evaluate cytoplasmic RNA content. The application of AO as a supplementary stain in surgical pathologic diagnosis is based on the premise that specific neoplastic cell types characteristically and consistently contain few or many cytoplasmic ribosomes. Primitive tumors such as Ewing's sarcoma and primitive neuroectodermal tumors showed negative or low-intensity AO-RNA cytoplasmic staining. Differentiated sarcomas such as rhabdomyosarcomas and lymphomas exhibited moderate to strong AO-RNA cytoplasmic fluorescence. Acridine orange--RNA staining provides an easy, convenient, and inexpensive adjunct in the histopathologic differential diagnosis of sarcomas. It is particularly useful for distinguishing Ewing's sarcomas from other small round cell sarcomas of childhood.

Fine structural localization of RNA in myeloma cells detected by the enzyme-gold method

The ultrastructural localization of RNA in myeloma cells was studied by the RNase-gold method. Gold particles indicating the presence of RNA were observed in large numbers, particularly in the granular component of the nucleolus and periphery of the rough endoplasmic reticulum, but not in the Golgi area, mitochondria, intranuclear inclusion bodies, cytoplasmic inclusion bodies, dense bodies, or cisternae of the rough endoplasmic reticulum. In the nuclear chromatin and nucleolus, gold particles were more numerous as these structures were less mature. They were found in larger numbers also in the cytoplasm of immature cells. In plasma cells from patients with macroglobulinemia, gold particles were fewer than in myeloma cells of multiple myeloma, but there was no difference in their distribution pattern.

Herpes simplex virus activates expression of a cellular gene by specific binding to the cell surface

The herpes simplex virus (HSV) type 1 mutant ts1204 attaches to the cell surface at 38.5 degrees but fails to penetrate the plasma membrane. A striking feature of human fetal lung cells infected with ts1204 at 38.5 degrees was the presence of enhanced amounts of a 56,000 molecular weight host protein, p56. Studies with protein and RNA synthesis inhibitors suggested that binding of the mutant virus to cells activated expression of the cellular gene encoding p56 and not an intermediary protein. Evidence presented in this paper supports the idea that p56 is induced by a specific interaction between ts1204 virions and the cell surface.

Spinal cord neurofibrillary tangles of Guamanian amyotrophic lateral sclerosis and parkinsonism-dementia complex: an immunohistochemical study

We studied the topographic distribution and immunohistochemical characteristics of spinal cord neurofibrillary tangles (NFTs) in 6 patients with Guamanian amyotrophic lateral sclerosis (ALS) and 6 patients with parkinsonismdementia complex (PD) on Guam, using antibodies to tau protein and ubiquitin. The NFTs were immunoreactive with both antibodies, but staining for tau was more pronounced. As identified by this reactivity, all the Guamanian ALS and PD cases examined showed spinal cord NFTs. The posterior horn had the most and the anterior horn the least. In the posterior horn the NFTs were located mainly in the marginal areas. Large anterior horn cells showed few, if any, NFTs. In addition to perikaryal NFTs, we observed tau-reactive neurites. Our results provide evidence that spinal cord NFTs are not uncommon in Guamanian ALS and PD on Guam and that they are more numerous than previously found with conventional methods.

A possible approach to enrich cDNA yields with full-length molecules

Newcastle disease virus (NDV)-specific hemagglutinin-neuraminidase (HN) mRNAs were used as the model templates for cDNA synthesis. Polyadenylated RNAs were isolated from the particulate fraction of cytoplasmic extracts of NDV-infected cells rather than from nonfractionated extracts. The approach is based on earlier findings that eucaryotic mRNAs are present in cytoplasmic extracts in the form of ribonucleoproteins (mRNPs) rather than as free nucleic acids. The idea of the approach was to separate mRNPs from cell sap RNases prior to RNA extraction in order to minimize partial enzymatic hydrolysis of mRNAs. The presence of the 5' terminus (mRNA sense) in cDNAs synthesized was considered as an indication for the suitability of mRNA templates for cDNA synthesis. The cDNAs were synthesized and cloned in lambda gt10 phage. About 300 phages carrying the HN-specific inserts have been identified among 50,000 recombinants, and nine of them were analyzed for the presence of the HN 5' terminus. It was found that the termini are present in all the clones analyzed. The result is in an agreement with the expectation that removal of cell sap prior to RNA extraction significantly increases the suitability of RNA templates for cDNA synthesis.

Cytoplasmic pH of Dictyostelium discoideum amebae during early development: identification of two cell subpopulations before the aggregation stage

Development of the cellular slime mold Dictyostelium discoideum is initiated by the removal of nutrients, and results in formation of a mature fruiting body composed of two cell types, the stalk and spore cells. A considerable body of evidence supports the hypothesis that cytoplasmic pH may be an essential regulator of the choice to differentiate in either the prestalk or prespore pathway. We have devised methods for measurement and analysis of intracellular pH in developing Dictyostelium amebae in order to assess directly the potential role of cytoplasmic pH in regulating the pathway of differentiation. The intracellular pH of single D. discoideum amebae during development and in intact slugs has been measured using the pH-sensitive indicator pyranine in a low light level microspectrofluorometer. We have used the ATP-mediated loading method to introduce pyranine into these cells. Cells loaded by the ATP method appear healthy, have no detectable defects in development, and exhibit a similar population distribution of intracellular pH to those loaded by sonication. The intracellular pH of populations comprised of single amebae was found to undergo a transient acidification during development resulting in a bimodal distribution of intracellular pH. The subpopulations were characterized by fitting two gaussian distributions to the data. The number of cells in the acidic intracellular pH subpopulation reached a maximum 4 h after initiation of development, and had returned to a low level by 7 h of development. In addition, a random sample of single amebae within a slug had a median intracellular pH of 7.2, nearly identical to the median pH (7.19) of similarly treated vegetative cells. No gradient of intracellular pH along the anterior to posterior axis of the slug was detected. Our data demonstrate the existence of two distinct subpopulations of cells before the aggregation stage of development in Dictyostelium, and offers support for the hypothesis that changes in intracellular pH contribute to development in D. discoideum.

The function of the vaccinia hemagglutinin in the proteolytic activation of infectivity

The vaccinia virus hemagglutinin (HA) has specific affinity for the structural protein, VP37K. The nature of this affinity and its relationship to the function of the HA were analyzed using HA mutants. The VP37K reactive site of the HA molecule is located in its transmembrane region, and the vaccinia virus HA associates with the viral particle via the VP37K-HA affinity. The viruses possessing an HA with fusion inhibitor activity were largely of the low infectivity form, whereas the viruses that associated mutant HAs defective in the activity were of the high infectivity form. D1 mutant virus does not produce HA. When it was incubated with the HA of the IHD-J strain, the HA associated with the virus particle. The HA-loaded D1 mutant virus acquired a high affinity not only for chick erythrocytes but also for KB and Vero cells. At the same time, the infectivity for Vero cells was decreased. The original high infectivity was recovered by treatment with trypsin. The virion-associated vaccinia HA has two functions; the HA protects the infectivity of the virus by the fusion inhibitor activity and exhibits affinity against host cells. Vaccinia virus first adsorbs to the cell via HA, and then proteolysis of the HA activates the second adsorption site which seems to be the fusogenic site of the virus. Proteolytic activation represents removal of the fusion inhibitor activity of the HA.

Intrinsic pituitary interleukin-1 beta is induced by bacterial lipopolysaccharide

Using a specific antiserum recognizing recombinant rat interleukin-1 beta (IL-1 beta), immunoreactive material was localized to cytoplasmic granules in anterior pituitary endocrine cells and colocalized with TSH in thyrotropes. Authenticity was established by Northern blot hybridization using a specific rat IL-1 beta cRNA probe, revealing a 1.8-kilobase mRNA identical to that in the spleen. The marked increase in anterior pituitary IL-1 beta message after the administration of bacterial lipopolysaccharide, raises the possibility that IL-1 beta may be involved in paracrine or autocrine regulation of pituitary function during infectious challenge.

The 56-59-kilodalton protein identified in untransformed steroid receptor complexes is a unique protein that exists in cytosol in a complex with both the 70- and 90-kilodalton heat shock proteins

It has previously been shown that 9S, untransformed progestin, estrogen, androgen, and glucocorticoid receptor complexes in rabbit uterine and liver cytosols contain a 59-kDa protein [Tai, P. K., Maeda, Y., Nakao, K., Wakim, N. G., Duhring, J. L., & Faber, L. E. (1986) Biochemistry 25, 5269-5275]. In this work we show that the monoclonal antibody KN 382/EC1 raised against the rabbit 59-kDa protein reacts with 9S, untransformed glucocorticoid receptor complexes in cytosol prepared from human IM-9 lymphocytes but not with 4S salt-transformed receptors. The human protein recognized by the EC1 antibody is a 56-kDa protein (p56) of moderate abundance located predominantly in the cytoplasm by indirect immunofluorescence. There are at least six isomorphs of p56 by two-dimensional gel analysis. N-Terminal sequencing (20 amino acids) shows that p56 is a unique human protein. When p56 is immunoadsorbed from IM-9 cell cytosol, both the 70- and 90-kDa heat shock proteins are coadsorbed in an immune-specific manner. Neither heat shock protein reacts directly with the EC1 antibody. We conclude that p56 exists in cytosol in a higher order complex containing hsp70 and hsp90, both of which in turn have been found to be associated with untransformed steroid receptors.

Immunohistochemical localization of the glucocorticoid receptor in pancreatic beta-cells of the rat

We used a monoclonal antibody against an epitope located in the N-terminal moiety of the rat glucocorticoid receptor to identify the glucocorticoid receptor-containing cells in the rat pancreas. Monospecific polyclonal antisera against insulin, glucagon, somatostatin, and amylase were applied to serial sections in colocalization studies to identify the respective endocrine and exocrine cells. Glucocorticoid receptor immunoreactivity was exclusively present in nuclei and cytoplasm of the beta-cells of pancreatic islets. Western blots using the glucocorticoid receptor antibody resulted in identical 94K immunoreactive proteins in both liver and pancreas. After adrenalectomy, the glucocorticoid receptor immunoreactivity of beta-cells decreased significantly. A computer-assisted method of semiquantitative evaluation of the glucocorticoid receptor immunoreactivity demonstrated a significant decrease in the staining intensity of the beta-cells by 23.5% and in that of insulin antibodies by 10.4%, while amylase immunoreactivity was only slightly decreased. Serum levels of corticosterone determined by RIA decreased from 225 micrograms/ml in sham-operated animals to 55 micrograms/ml in animals 14 days after adrenalectomy, while the tissue content of amylase decreased by 45%. The immunohistochemical findings give circumstantial evidence of the presence of glucocorticoid receptor in beta-cells. We interpret our data as indicating an indirect effect of glucocorticoids on amylase synthesis via a glucocorticoid-insulin-exocrine cell pathway.

Detection of intracellular expression and secretion of interferon-gamma at the single-cell level after activation of human T cells with tetanus toxoid in vitro

Activation of T cells results in intracellular expression and secretion of cytokines such as interferon (IFN)-gamma. Here we have used three different assays for determination of IFN-gamma in tetanus toxoid- or mitogen-activated human T cell cultures. Two of these assays [intracytoplasmic immunofluorescence and enzyme-linked immuno spot assay (ELISPOT)] determined the expression and secretion of IFN-gamma at the single-cell level while the third assay enzyme-linked immunosorbent assay (ELISA) measured IFN-gamma secreted into the culture supernatant. Comparison of all three tests revealed a good correlation between the ELISPOT assay and the ELISA, whereas expression of intracellular IFN-gamma showed a qualitative but not a quantitative correlation with the latter. Both the immunospot assay and the immunofluorescence may be used to detect approximate numbers of specific T cells even when present at low frequencies. With the use of the immunospot assay antigen-specific T cells could be detected even in the absence of detectable IFN-gamma in the culture supernatants. However, the ELISA assay should be more convenient for screening large clinical material.

Conservation of a cytoplasmic carboxy-terminal domain of connexin 43, a gap junctional protein, in mammal heart and brain

According to the sequence of connexin 43, a cardiac gap junctional protein, the domain contained within residues 314-322 is located 60 amino acids away from the carboxy-terminus. Antibodies raised to a peptide corresponding to this domain label a unique 43-kD protein on immunoblots of both purified gap junctions and whole extracts from rat heart. Immunofluorescence investigations carried out on mammal heart sections reveal a pattern consistent with the known distribution of intercalated discs. Immunogold labeling performed with ultrahin frozen sections of rat heart or partially purified rat heart gap junctions demonstrate that antigenic determinants are associated exclusively with the cytoplasmic surfaces of gap junctions. The antibodies were shown to cross-react with a 43-kD protein on immunoblots of whole extracts from human, mouse and guinea pig heart. However, no labeling was seen when heart of lower vertebrates such as chicken, frog and trout, was investigated. These results, confirmed by immunofluorescence investigations, were interpreted as a loss of antigenic determinants due to sequence polymorphism of cardiac connexin 43. Proteins of Mr 43 and 41 kD, immunologically related to cardiac connexin 43, were detected in immunoblots of mouse and rat brain whole extracts. mRNAs, homologous to those of cardiac connexin 43 and of the same size (3.0 kb), are also present in brain. Immunofluorescence investigations with primary cultures of unpermeabilized and permeabilized mouse neural cells showed that the antigenic determinants recognized by the antibodies specific for connexin 43 are cytoplasmic and that the labeling observed between clustered flat cells, is punctate, as expected for gap junctions. Double labeling experiments demonstrated that the immunoreactivity is associated with GFAP-positive cells, that is to say, astrocytes.

A major glycoprotein of the nuclear pore complex is a membrane-spanning polypeptide with a large lumenal domain and a small cytoplasmic tail

One of a small number of polypeptides of the nuclear pore complex that have been identified is a major glycoprotein called gp210. Since it is very resistant to chemical extractions from membranes, gp210 was suggested to be integrated into nuclear membranes. In this study we have determined the membrane topology of this protein by biochemical and immunological approaches. We found that limited proteolysis of isolated nuclear envelopes with papain released a 200 kd water-soluble fragment of gp210 containing concanavalin A-reactive carbohydrate. Immunogold electron microscopy with a monoclonal antibody showed that this domain is localized on the lumenal side of nuclear membranes at pore complexes. Anti-peptide antibodies against two sequences near the C-terminus of gp210 were used to map possible membrane spanning and cytoplasmically disposed regions of this protein. From analysis of the protease sensitivity of these epitopes in sealed membrane vesicles, we determined that gp210 contains a small cytoplasmic tail and only a single membrane-spanning region. Thus, gp210 is a transmembrane protein with most of its mass, including the carbohydrate, located in the perinuclear space. This topology suggests that gp210 is involved primarily in structural organization of the pore complex, for which it may provide a membrane attachment site.

Distribution of fodrin in the keratinocyte in vivo and in vitro

Distribution of fodrin in the keratinocyte, both in vivo and in vitro, was examined by immunofluorescence microscopy. In the rat epidermis in vivo, fodrin was localized in the cell periphery of the spinous layer of all the skins studied. In only the basal layer of the thick skin, however, fodrin was seen intensely in the cytoplasm. As in vitro keratinocytes, a mouse cell line (Pam 212) cultured in low (0.06 mM) as well as standard (1.87 mM) Ca2+ was examined. In low Ca2+, fodrin was observed throughout the cytoplasm without marked accumulation irrespective of the cell density. The cytoplasmic labeling in low Ca2+ looked filamentous and became aggregated when cells were treated with cytochalasin B; at least some of the aggregates coexisted with those of F-actin. In contrast, fodrin distribution was not affected with colchicine. On the other hand, in standard Ca2+, the protein became concentrated along the cell periphery and less conspicuous in the cytoplasm as the cells reached confluency. When cells were transferred from low to standard Ca2+, the distribution of fodrin changed accordingly within 180 min. The present results indicate that fodrin in the keratinocyte is likely to be associated with actin filaments and that it takes two different ways of distribution both in vivo and in vitro. The peripheral and the cytoplasmic labeling of in vivo and in vitro cells are likely to correspond. It may be that fodrin changes its localization according to the cell's proliferative activity.

Interleukin 2 production by a marmoset B cell line

Several B cell lines constitutively secreting interleukin (IL) 2 were derived from the Epstein-Barr virus-positive marmoset B cell line, B95-8. A representative line, KRC-18, was cloned by limiting dilution and found to be 40% surface IgM+, 60% cytoplasmic IgM+, greater than 95% DR+, weakly Tac+ and devoid of T cell, monocyte and NK cell surface antigens. Supernatant from KRC-18 cells supported the long-term growth of an IL 2-dependent murine T cell line, HT-2, and contained 7-8 units/ml of IL 2 activity when compared to recombinant IL 2. The supernatant was fractionated by Sephadex G-75 gel filtration, and maximal proliferation of HT-2 cells was supported by the 20-22-kDa column fraction. The proliferative response of HT-2 cells to KRC-18 supernatant was inhibited by monoclonal antibodies to human IL 2 or the murine IL 2 receptor in a dose-dependent manner, suggesting that the KRC-18 IL 2 has epitopes that are similar to human IL 2, and that its activity is mediated through binding to the IL 2 receptor of the target cell line. When KRC-18 cells were analyzed for cytoplasmic IL 2, greater than 90% of the cells contained intracellular IL 2 in amounts equivalent to, or greater than, mitogen-activated T cells. These data indicate that certain B lineage cell lines are capable of IL 2 synthesis and secretion.

A Hoechst H33258 agarose plate assay for the estimation of nanogram DNA levels without RNA interference: applications in PCR and in estimations of plasmid and cytoplasmic DNA

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