Acyl-GPC and alkenyl/alkyl-GPC:acyl-CoA acyltransferases

In mammalian tissues, phosphatidylcholine, or 1,2-diacyl-glycerophosphocholine (GPC), is the most abundant form of choline-containing phospholipids. In some electrically active tissues, a significant portion of the choline-containing phospholipids is 1-alkenyl-2-acyl-GPC (plasmenylcholine). The 1-alkyl-2-acyl-GPC is found in significant amounts in circulating cells such as neutrophils and macrophages but in low amounts in other tissues. Structural studies of phosphatidylcholine indicate that there is an asymmetric distribution of acyl groups on the molecule. Saturated fatty acids are usually esterified at the sn-1 position of the glycerol backbone, whereas unsaturated fatty acids are esterified at the sn-2 position. Similarly, unsaturated acyl groups are usually found in the sn-2 position of plasmenylcholine. The remodelling of the sn-2 acyl group in phosphatidylcholine by the deacylation-reacylation process has been demonstrated in a number of tissues. Phospholipase A2 is responsible for the hydrolysis of the acyl group at the sn-2 position, whereas 1-acyl-GPC:acyl-CoA acyltransferase is responsible for the reacylation reaction. The acyltransferase is located in the microsomal fraction and displays specificity towards the polyunsaturated acyl groups. The enzyme can be solubilized by detergent, but the enzyme activity in soluble form is difficult to maintain. The acyltransferase for the reacylation of 1-alkenyl-GPC is also located in the microsomal fraction and is somewhat specific towards polyunsaturated acyl groups. In guinea pig heart mitochondria, however, a new form of 1-alkenyl-GPC acyltransferase was identified which appeared to be different from the microsomal form. The acyltransferase for the acylation of 1-alkyl-GPC into platelet-activating factor has been studied in several tissues including human neutrophils. At present, the contribution of the acyltransferase in attaining the observed molecular composition of the choline-containing phospholipids in the tissue has not been defined. We postulate that the intrinsic acyl-CoA specificity of the acyltransferase, the flux of 1-acyl-GPC, 1-alkenyl-GPC and 1-alkyl-GPC, as well as the pool size of acyl-CoA are major factors in producing the final composition of the molecular species of the choline-containing phospholipids.

The modulation of choline phosphoglyceride metabolism in human colon cancer

Colorectal cancer has a high incidence of morbidity and mortality in the North American population. Elevated levels of plasmalogens have been reported in some neoplastic tissues including colon tumors, but the mechanism for this increase has not been defined. Since changes in plasmalogen level are usually associated with changes in the other phospholipid subclasses, a general increase in all phospholipid subclasses may also be found in colonic neoplasms. In this study, the levels of the major phospholipids, including their plasmalogen and diacylphospholipid subclasses, were found to be elevated in human malignant colonic tissues. Since phosphatidylcholine is the most prominent type of phospholipid found in both malignant and control tissues, the mechanism for its accumulation during malignancy was investigated. Decreases in phospholipase C and D activities were observed in tumor samples, but an enhancement of the CTP: phosphocholine cytidylyltransferase activity was also detected. Immunoblotting analysis revealed that the elevated cytidylyltransferase activity was caused by a three-fold increase in the level of enzyme protein during tumor development. Based on these enzyme studies, we conclude that the high level of phosphatidylcholine in colon tumors resulted from a decrease in its turnover and an increase in its expression.

Allergen-driven limiting dilution analysis of human IL-4 and IFN-gamma production in allergic rhinitis and clinically tolerant individuals

Difficulties in detecting human IL-4 synthesis in antigen-driven primary culture have led to widespread reliance on less physiologic approaches to T cell activation. Although there is general agreement of a Th2-like bias, the precise defects in cytokine responsiveness remain controversial. Analysis of cytokine protein production by fresh, unselected cell populations in response to cognate, antigen-driven stimulation remains an important goal. Here, limiting dilution analysis (LDA) was used to evaluate antigen-stimulated cytokine gene expression by fresh peripheral blood mononuclear cells (PBMC). PBMC from 19 grass pollen sensitive, allergic rhinitis subjects and normal, non-atopic controls were evaluated 1 month after natural reimmunization (the peak of the local grass pollen season). Surprisingly, highly atopic subjects and clinically non-allergic individuals exhibited virtually equivalent antigen-specific, CD4-dependent cytokine production in response to short-term culture with these common environmental antigens. As anticipated, pronounced increases in Th2-like activity were evident in the circulating immune repertoire of grass pollen sensitive individuals, leading to a median ratio of antigen-stimulated IFN-gamma:IL-4 frequencies of 117:1 among normal subjects versus 4:1 among those with allergic rhinitis (Mann-Whitney U-test, P = 0. 00067). This Th2-like bias reflected both a lower frequency of IFN-gamma-producing cells and a markedly increased frequency of IL-4-producing cells in the circulating grass-pollen specific repertoire of atopic donors. The observation that every atopic and normal subject produced IFN-gamma (+/-IL-4) following antigen re-stimulation argues that the decision as to whether allergy or (clinical) tolerance results, hinges not on a genetically determined capacity of whether allergen-reactive T cells can be stimulated in any given individual by chronic exposure to ubiquitous environmental antigens, but on the nature of the cytokine response that comes to dominate that individual's response.

Allergen-stimulated interleukin-4 and interferon-gamma production in primary culture: responses of subjects with allergic rhinitis and normal controls

The balance of interleukin-4 (IL-4) to interferon-gamma (IFN-gamma) production that is induced following exposure to common environmental antigens is believed to be instrumental in determining whether hypersensitivity or clinical unresponsiveness results to that antigen. To date, evaluation of cytokine (protein) production has been based predominantly on allergen-reactive CD4 T-cell clones or activation of fresh unselected peripheral blood mononuclear cell (PBMC) populations with non-physiological stimuli such as phorbal myristate acetate (PMA) and calcium ionophore, phytohaemagglutinin (PHA), anti-CD3 or anti-CD2/anti-CD28 monoclonal antibodies (mAb). Here, ultrasensitive IL-4 and IFN-gamma assays were optimized to allow direct analysis of antigen-stimulated cytokine production by fresh human PBMC. Primary cultures of cells from grass pollen-sensitive allergic rhinitis subjects and non-atopic controls were stimulated using a range of grass pollen allergen concentrations in the absence of exogenous cytokines or polyclonal activators. The majority of subjects (45 of 52) exhibited chloroquine-sensitive, CD4-dependent cytokine production in allergen-stimulated, short-term primary culture. Median IL-4 production was substantially greater among atopics (13.0 pg/ml versus < 1 pg/ml, Mann-Whitney U test, P < 0.0000001) and IFN-gamma was lower (P = 0.008), providing direct evidence for an imbalance in both IL-4 and IFN-gamma production among circulating, pollen-reactive cells in individuals with seasonal allergic rhinitis. The distinction in the allergen-driven cytokine responses elicited from normal and atopic donors was underscored by examination of the ratios of IFN-gamma:IL-4 synthesis. Non-atopic individuals exhibited intense IFN-gamma dominance of the T-cell response, in marked contrast to that observed among grass pollen-sensitive individuals (median IFN-gamma:IL-4 ratios of 14.0 versus 0.096, P = 0.000002). The observation that essentially all individuals produced IFN-gamma (+/- IL-4) following antigen stimulation in vitro argues that the most relevant consideration in determining susceptibility to immediate hypersensitivity versus clinical tolerance to environmental allergens is not a genetically defined capacity to recognize the antigen (i.e. if allergen-reactive T cells are present in that individual) but the nature of the cytokine response.

Antigen mediated and polyclonal stimulation of human cytokine production elicit qualitatively different patterns of cytokine gene expression

Polyclonal activators are widely used as surrogate antigens in analysis of human cytokine gene expression. An implicit assumption is that the T cell activation and cytokine production observed in response to polyclonal activation provides a more intense, but qualitatively identical, reflection of results that would be obtained with antigen. Here we demonstrate that stimulation using accessory cell independent (immobilized anti-CD3 mAb) or dependent [phytohemagglutinin (PHA) or soluble anti-CD3 mAb] polyclonal activators yields different conclusions from those that are obtained in response to antigen-specific T cell activation. Cytokine synthesis in 1-5 day bulk cultures of fresh peripheral blood mononuclear cells (PBMC) from 52 subjects evenly divided between grass pollen sensitive allergic rhinitis subjects and normal, non-atopic controls were examined. Antigen-specific re-stimulation elicited elevated IL-4 and IL-10 production and lower IFN-gamma synthesis among allergic subjects than normal non-atopic control subjects. This commitment of fresh PBMC towards a Th2-like response in atopics and the dominance of the IFN-gamma response seen in non-allergic subjects was reinforced when the ratio of IFN-gamma:IL-4 production in bulk culture was examined. Atopic individuals exhibited median IFN-gamma:IL-4 values of 0.07, whereas grass pollen stimulated cytokine production by normal subjects yielded a ratio of 4.8. In marked contrast, IL-2, IL-4, IL-10 and IFN-gamma production elicited using polyclonal activators, though much more intense, did not differ between allergic and non-allergic subjects (Wilcoxon rank sum test P > > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Limiting dilution analysis of antigen stimulated IL-4 and IFN-gamma production in human mononuclear cell populations

Limiting dilution analysis (LDA) of fresh human mononuclear cell populations has previously been used to estimate the frequency of specific B cells, CTL, proliferative T cells, or cells capable of IL-2 production in various clinical situations. Such approaches evaluate the intensity of the response but provide little information concerning the balance between Th1- vs. Th2-like patterns of cytokine gene expression. Here, we describe development of an LDA method to obtain quantitative estimates of the frequency of antigen-specific IFN-gamma or IL-4 producing cells in human peripheral blood. The approach utilizes 3-4 day antigen-mediated restimulation of mononuclear cell populations freshly derived from grass pollen sensitive allergic rhinitis subjects. IFN-gamma and IL-4 production in culture supernatants are determined by ELISA and CT.h4S bioassay. Cytokine production elicited in this assay is CD4 dependent and antigen specific. As such, it provides a useful non-invasive approach for rapid evaluation of low frequency, antigen-induced cytokine production in the circulating repertoire. This method can readily be extended to analysis of other cytokines in other immunologic disorders or in infectious disease states, allowing longitudinal analysis of individuals and facilitating efforts to establish clear correlations between in vivo patterns of cytokine gene expression and disease exacerbation and remission.

Purification, characterization and modulation of a microsomal carboxylesterase in rat liver for the hydrolysis of acyl-CoA

A carboxylesterase containing long-chain acyl-CoA hydrolase activity was purified to apparent homogeneity from rat liver microsomes. Palmitoyl-CoA was the most preferred substrate, followed by stearoyl-CoA and oleoyl-CoA. Arachidonoyl-CoA, linoleoyl-CoA and acetyl-CoA were not hydrolysed by the enzyme. The purified enzyme had no activity on the hydrolysis of phospholipids and neutral lipids. The molecular mass of the enzyme was found to be 56 kDa by SDS/PAGE and 64 kDa by gel-filtration chromatography. On isoelectric focusing, the purified enzyme behaved like the ES-4 type, with a pI of 6.15. Determination of the amino acid sequence revealed that its N-terminal sequence is 100% homologous with the only other known N-terminal sequence for a rat carboxylesterase isoenzyme (ES-10). Enzyme activity was inhibited by lysophosphatidic acid and activated by lysophosphatidylcholine. The modulation of enzyme activity by these lysophospholipids might represent a plausible mechanism for the physiological control of acyl-CoA concentrations.

Human interferon-gamma has three domains associated with its antiviral function: a neutralizing epitope typing scheme for human interferon-gamma

An antiviral activity-neutralizing monoclonal antibody (mAb), MIF3037, was developed by the immunization of BALB/c mice with recombinant human interferon-gamma (rhuIFN-gamma). Its neutralizing activity suggests that its epitope may be at or adjacent to a functional domain on the huIFN-gamma. MIF3037 was compared with representative mAb of previously identified epitope-specific groups in a competitive binding assay. In an attempt to determine if there are other functional epitopes recognized by mAb developed with different preparations of huIFN-gamma or different hybridoma screening methods, 14 additional mAb contributed by five other laboratories were similarly analysed. Based on their ability to bind to huIFN-gamma, all the neutralizing mAb except MIF3037 may be classified into three previously defined groups: E1, E2 and E1/E2. Monoclonal antibodies of the E1 group do not compete with those of the E2 group for huIFN-gamma binding, indicating that the E1 and E2 epitopes are distinct domains on the huIFN-gamma important for the antiviral function. Monoclonal antibodies of the E1/E2 group compete with some of the mAb of E1 and/or E2 groups and may bind to regions of the huIFN-gamma that partially overlap the E1 and E2 epitopes. MIF3037 demonstrated no competitive binding inhibition with mAb of the previously identified epitope specificity groups and, therefore, must represent a distinct functional epitope, E3. The huIFN-gamma, therefore, must have at least three distinct functional domains; none of these appeared to be responsible for cell surface receptor binding. Based on this finding, the epitope typing scheme must be extended to include the E3 epitope. The epitope specificity relationships of 13 neutralizing mAb developed by five other laboratories were established which allows correlation of results obtained with these mAb by different laboratories. The location of the epitopes of four widely studied mAb, 69B, 73A, 113B and 220A12, have been deduced based on their competition with the E1 mAb which have recently been mapped.

Identification of highly conserved and species-specific polypeptides of Haemophilus ducreyi

Chancroid is a sexually transmitted diseased caused by Haemophilus ducreyi. The pathological manifestations of chancroid are unique among Haemophilus species and the virulence factors of H. ducreyi that account for these features have not been identified. Some of these virulence factors may be unique components of H. ducreyi, but attempts to identify H. ducreyi-specific components have been unsuccessful. Four polypeptides--A, B, C and D of 83, 77, 56 and 28 kDa, respectively--were identified with a panel of nine H. ducreyi-specific monoclonal antibodies (MAbs). Polypeptide C was one of the five major proteins in H. ducreyi and demonstrated micro-heterogeneity in SDS-PAGE. Polypeptides A, B and D were present in only small amounts in whole-cell lysates of H. ducreyi. The relative amounts of A and B varied, suggesting that they may be precursor molecules. The unique polypeptides C and D were not exposed on the surface. Polypeptide C was highly soluble and did not appear to be membrane-bound, whereas polypeptide D appeared to partition with the cytoplasmic membrane and was soluble in Sarkosyl. All four polypeptides appeared to be unique to H. ducreyi since MAbs directed against them did not cross-react with H. influenzae, H. parainfluenzae or Neisseria gonorrhoeae. The mol. wts of all of these polypeptides were conserved throughout 35 clinical isolates collected from 15 cities in eight countries and one reference strain of H. ducreyi that were tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney-21 cells

The effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney (BHK-21) cells were investigated. The cells were incubated with labelled choline in the presence of an amino acid or ethanolamine. The uptake of labelled choline was noncompetitively inhibited by amino acids. Glycine, L-alanine, L-serine, L-leucine, L-aspartate, and L-arginine were effective inhibitors and a maximum of 22% inhibition of choline uptake was obtained with 5 mM glycine. Analyses of the labelings in the choline-containing metabolites revealed that the conversion of choline to CDP-choline and subsequently phosphatidylcholine was not affected by the presence of amino acids. The uptake of choline was also inhibited by ethanolamine in a concentration-dependent manner. Kinetic studies on the uptake of choline indicated that the inhibition by ethanolamine was competitive in nature. Although ethanolamine is a potent inhibitor of choline kinase, analyses of the labelings in the choline-containing metabolites indicated that the conversion of choline to phosphocholine was not affected in the cells incubated with ethanolamine. Ethanolamine did not change the pool sizes of phosphocholine and CDP-choline. Based on the specific radioactivity of CDP-choline and the labeling of phosphatidylcholine, the rates of phosphatidylcholine biosynthesis were not significantly different between the control and the ethanolamine-treated cells. In view of the concentrations of amino acids (millimolar) and ethanolamine (micromolar) in most cell culture media, it appeared that only amino acids were important metabolites for the regulation of choline uptake in BHK-21 cells. We conclude that both amino acids and ethanolamine have no direct effect on the biosynthesis of phosphatidylcholine.

The E1 functional epitope of the human interferon gamma is a nuclear targeting signal-like element. Mapping of the E1 epitope

Eight neutralizing monoclonal antibodies (mAbs) directed against the human interferon gamma (HuIFN-gamma) that were classified in the E1 epitope group were mapped by the synthetic peptide approach. A set of 136 octapeptide homologs of the 143-residue primary sequence of the HuIFN-gamma, each one with a 7-residue sequence overlap with successive peptide, was synthesized. Based on the similar reactivity patterns of all the mAbs with this set of synthetic peptides, the E1 functional epitope was localized to residues 84-94 on the HuIFN-gamma. The epitope sequence is: Ser-Asn-Lys-Lys-Lys-Arg-Asp-Asp-Phe-Gln-Lys. The fact that eight independently isolated mAbs binding to the same domain can neutralize the HuIFN-gamma activity suggests that the E1 domain must be at or adjacent to a functional site. Within this domain is a sequence element, Lys-Lys-Lys-Arg, that resembles the nuclear location signals known to effect the intracellular transportation of a number of nuclear proteins, such as the large tumor antigen (T antigen) of simian virus 40 (SV40) and polyoma virus and steroid hormone receptors. This observation suggests that the HuIFN-gamma molecule and/or its complex with the receptor must function in the nucleus to effect transcription regulation that results in the various biological activities. The signal for that intracellular transportation must be provided by the HuIFN-gamma molecule.

Structure-function analysis of the human interferon gamma. The COOH terminus is not essential for functional activity

The structure-function relationships for the human interferon gamma (HuIFN-gamma) were studied using recombinant variants that had various deletions at the carboxyl terminus. Four COOH-terminal deletion variants were constructed that contained the amino-terminal 122, 117, 111, and 106 amino acid residues. These variants were constructed by specific DNA modifications and were expressed in Escherichia coli. The deletion of 21 amino acid residues resulted in only 2- and 3-fold reduction in the antiviral and antiproliferative specific activities, respectively. Thus, the carboxyl-terminal 21 residues are not directly involved in the function of the HuIFN-gamma. The level of intracellular accumulation was also decreased by 3-5-fold. Further deletions of 26, 32, and 37 residues from the COOH terminus resulted in the lack of detectable activity as well as in 50-100-fold reduction in the level of accumulation in the bacterial cell. However, each of the modified plasmids was found to have comparable efficiency in directing the production of the respective variant molecules relative to the full-length HuIFN-gamma molecule in an in vitro transcription-translation assay. Thus, the failure of some of the deletion variant molecules to accumulate in the E. coli cell is likely due to their instability in vitro. The loss of the COOH-terminal 21 amino acid residues of HuIFN-gamma also resulted in a substantial reduction in the ability of the molecule to be renatured in vitro from the treatment with chaotrophic agents, a method frequently used to extract and purify recombinant polypeptides from E. coli host. The latter result may account for some earlier reports which inferred the involvement of the COOH terminus in the functions of the HuIFN-gamma molecule due to their failure to detect activity upon deletions of only 11-18 residues.

Immunobiological study of interferon-gamma-producing cells after staphylococcal enterotoxin B stimulation

Staphylococcal enterotoxin B (SEB) induced the production of human interferon-gamma (hIFN-gamma) in peripheral blood mononuclear cells (PBMC). Using specific mouse monoclonal antibodies (mAb) to hIFN-gamma, the patterns of cytoplasmic fluorescence in the PBMC from five individuals were studied. Discrete polar bodies in a ring-formation adjacent to the nuclear membrane was the most frequently observed fluorescent pattern throughout the 76-hr observation period. Additional and different fluorescent patterns such as multifocal and diffused cytoplasmic, as well as granular fluorescence over the whole cytoplasm, may appear during the late induction period (50-76 hr). By using an immunogold-silver (IGS) enhancement method to label cell-surface antigens, it was possible to detect the presence of CD3, CD4, CD25 and OKT11 marker in 55%, 54%, 77%, and 71% of the IFN-gamma producer cells, respectively. Monensin and carboxylcyanide m-chlorophenyl-hydrozone (CCCP) are ionophores known to interrupt subcellular transport of a number of secretory proteins. When monensin or CCCP was added to the induced cultures 2-3 hr before harvests, an increase in the intensity of cytoplasmic fluorescence in IFN-gamma-producing cells was observed; a greater than 10-fold enhancement in the sensitivity of immunostaining was demonstrated in these preparations.

Production of monoclonal antibodies specific for Haemophilus ducreyi: a screening method to discriminate specific and cross-reacting antibodies

Haemophilus ducreyi is the etiological agent of chancroid. The organism shares extensive immunological cross-reactivity with other Haemophilus species. This presents substantial difficulties for the production of specific monoclonal antibodies (MAbs). A competition ELISA was devised for hybridoma screening which allowed the detection of H. ducreyi-specific antibody-producing hybridoma cultures during the initial screening process. With this screening method, seven MAbs specific for H. ducreyi were obtained in a single cell fusion exercise. The specificities of the 7 MAbs were demonstrated by direct ELISA and dot immunobinding assays against several strains each of H. influenzae, H. parainfluenzae and Neisseria gonorrhoeae. Five of the MAbs reacted against all ten strains of H. ducreyi. These MAbs may permit the development of rapid and efficient immunodiagnostics for chancroid. The principle of the competition ELISA for hybridoma screening should be widely applicable to the development of specific MAbs to other organisms in which immunological cross-reactivity is an impediment to hybridoma screening by conventional methods.

Infectivity-deficient vesicular stomatitis virus produced in the presence of interferon has a functional virion core

Interferon induces two antiviral actions against vesicular stomatitis virus by (i) inhibiting viral protein synthesis which leads to a reduction in virion production, and (ii) producing progeny which are deficient in infectivity (VSVIF). At low or physiological concentrations of interferon, while the virion production was decreased by less than 10-fold, the virion infectivity yield was suppressed more than 1000-fold. The VSVIF was found to be deficient (quantitatively) in envelop glycoprotein G and protein M. Tryptic peptide mapping indicated that there was no detectable structural abnormality in the G, M, and N proteins of VSVIF. The virion cores, lacking only the envelop G protein, isolated from VSVIF and control VSV have essentially identical specific infectivity. This indicated that the virion proteins L, N, NS, and M, as well as viral RNA that make up the virion core, must be functionally normal, and the observed deficiency in G protein was likely to be the cause of the functional deficiency of the virion. Low concentrations of DEAE-dextran, which is known to partially overcome the virion's dependence on the G protein for adsorption to the cell during infection, were found to enhance the infectivity of VSVIF more than the control virion. These results together indicated that the loss of infectivity in the VSVIF was due to the deficiency of the surface glycoprotein G.

Distinct domains of recombinant human IFN-gamma responsible for anti-viral effector function

A panel of 21 independently isolated neutralizing mAb directed against the human rIFN-gamma (rHuIFN-gamma) was used to characterize those epitopes that are involved in the antiviral function of the rHuIFN-gamma. A sandwich competition assay was developed to determine the cross-reactivities between the mAb. The 125I-labeled mAb were allowed to compete with varying amounts of unlabeled mAb for binding to rHuIFN-gamma under Ag-limiting conditions, and the 50% inhibition endpoints were determined for each of the 21 mAb. The competition of each heterologous mAb relative to the competition of the homologous mAb was determined. By grouping the competition patterns of the 21 mAb, it was apparent that at least two epitopes (E1 and E2) were important to the antiviral function of rHuIFN-gamma. The possibility of the separation of the receptor binding site and signal transduction effector site(s) is discussed.

Distinct domains of recombinant human IFN-gamma responsible for anti-viral effector function

A panel of 21 independently isolated neutralizing mAb directed against the human rIFN-gamma (rHuIFN-gamma) was used to characterize those epitopes that are involved in the antiviral function of the rHuIFN-gamma. A sandwich competition assay was developed to determine the cross-reactivities between the mAb. The 125I-labeled mAb were allowed to compete with varying amounts of unlabeled mAb for binding to rHuIFN-gamma under Ag-limiting conditions, and the 50% inhibition endpoints were determined for each of the 21 mAb. The competition of each heterologous mAb relative to the competition of the homologous mAb was determined. By grouping the competition patterns of the 21 mAb, it was apparent that at least two epitopes (E1 and E2) were important to the antiviral function of rHuIFN-gamma. The possibility of the separation of the receptor binding site and signal transduction effector site(s) is discussed.

Production of monoclonal antibodies against recombinant human interferon-gamma: screening of hybridomas without purified antigen

A panel of mouse monoclonal antibodies (MAbs) against the recombinant human gamma interferon (HuIFN-gamma) has been produced for the study of the structure-function relationships of this important lymphokine. Enzyme linked immunosorbent assay (ELISA) is the current method of choice to screen hybridomas for specific MAb production. The purity of the antigen used for screening dictates the specificity of the ELISA. As often is the case in many systems, adequately purified biologically active HuIFN-gamma was not readily available for this purpose. A sandwich ELISA which allowed the use of unpurified HuIFN-gamma for hybridoma screening was developed. A rabbit antiserum against the denatured HuIFN-gamma purified by SDS-PAGE was prepared and the nonspecific binding activity was removed by adsorption to control cell proteins immobilized on Sepharose. The adsorbed immunoglobulin fraction was bound to the ELISA plate: (i) to trap HuIFN-gamma specifically from the whole cell lysate, thus providing specificity for MAb detection, and (ii) to avoid direct adsorption of the HuIFN-gamma to the ELISA plate because others have found that this prevented detection of neutralizing MAb. The sandwich ELISA detected both neutralizing and non-neutralizing MAbs with relatively low false positive reactions. This approach to the development of an ELISA method to screen hybridomas without purified antigen should be applicable to the production of MAbs to other proteins.

Interferon induces the production of membrane protein-deficient and infectivity-defective vesicular stomatitis virions through interference in the virion assembly process

The reduced rate of synthesis, maturation and degradation as well as the level of accumulation of the intracellular virus proteins in VSV-infected cells may account for the overall reduction (less than 10-fold) of progeny virion yield due to interferon (IFN); however, the deficiency of the virions proteins, G and M, which apparently caused a drastic loss of infectivity of these progeny virions (about 1000-fold) cannot be easily explained, because the concentrations of G and M proteins relative to other virus proteins were not reduced in the cell. In fact, intracellular M protein was significantly increased. Moreover, the virus proteins in IFN-treated and control cells were synthesized and accumulated in large excess of the amount incorporated into the released virions. The reduction in the intracellular activity of GlcNac-P-P-Dol transferase did not appear to play a direct role in the antiviral mechanism in this system. Our results, however, do suggest that the deficiency of G and M proteins in the virion is related to specific inhibition of the incorporation of either or both of these proteins in the virus assembly process.

Eukaryotic translational control: adeno-associated virus protein synthesis is affected by a mutation in the adenovirus DNA-binding protein

Growth of adeno-associated virus (AAV) requires expression of certain adenovirus (Ad) genes in the same cell. AAV particles contain three proteins, VP1 (Mr 85,700), VP2 (Mr 72,000), and VP3 (Mr 61,500). These proteins have overlapping peptide maps. We recently reported that AAV RNAs make up a 3'-coterminal family of overlapping molecules. We report here that the most abundant AAV mRNA, a 2.3-kilobase spliced RNA, codes for all three proteins--VP1, VP2, and VP3--when translated in an in vitro reticulocyte lysate. This shows that the AAV capsid proteins are coded by the genome sequence between map positions 48.0 and 96.0 (1 map unit is 1% of the genome or 47 base pairs). When AAV was grown in human KB cells with the Ad temperature-sensitive mutant Ad5ts125 at the nonpermissive temperature (40 degrees C), the accumulation in vivo of AAV capsid proteins VP1, VP2, and VP3 was decreased to less than 1/50th. However, normal amounts of the 2.3-kilobase mRNA were accumulated, and this RNA could be efficiently translated in an in vitro reticulocyte lysate system to yield VP1, VP2, and VP3. These experiments suggest that in infected cells control is exerted upon the AAV 2.3-kilobase mRNA at the translational level and that this control can be influenced by mutations in Ad. These Ad mutations map in the region 2 early gene for the Ad DNA-binding protein. The temperature-sensitive system that we have studied may be useful for analysis of translational control of a eukaryotic mRNA.

Adenovirus helper function for growth of adeno-associated virus: effect of temperature-sensitive mutations in adenovirus early gene region 2

Adeno-associated virus (AAV) grows efficiently only in cells that are also infected with an adenovirus (Ad). We employed Ad mutants to determine which genes may be required for the AAV helper function. Two mutants of Ad type 5 (Ad5), Ad5ts125 and Ad5ts107, with temperature-sensitive lesions in the E72 DNA-binding protein coded by the Ad early region 2, were deficient for AAV helper functions at the nonpermissive temperature (40 degrees C). In contrast, Ad5ts149, with a temperature-sensitive lesion in the Ad early region 5, was an efficient helper of AAV at the nonpermissive temperature. In KB cells, with the Ad5ts125 or Ad5ts107 mutant as the helper, the accumulation of AAV capsid proteins and AAV particles was decreased by about two logs, whereas AAV DNA synthesis was decreased only severalfold. Cytoplasmic, polyadenylic acid-containing AAV RNA is composed of a set of overlapping, spliced RNAs having different 5' start points. With the ts125 helper at 40 degrees C there was a decreased accumulation of some but not all of these AAV RNAs. The Ad5 E72 protein may have an effect on transcription or more likely posttranscriptional processing of AAV RNA. These observations suggest additional pleiotropic effects of the multifunctional E72 protein and suggest further similarities in the actions of E72 and the simian virus 40 T-antigen.

Selective inhibition of glycoprotein and membrane protein of vesicular stomatitis virus from interferon-treated cells

A 200-fold inhibition in the titer of infectious vesicular stomatitis virus (VSV) was produced in cultures of Ly cells treated with 30 reference units of interferon per milliliter. Virus particle production, as measured by VSV particle-associated transcriptase, or nucleocapsid protein was inhibited by a maximum of tenfold. The glycoprotein and membrane protein content was reduced in VSV derived from interferon-treated cells. Thus interferon-treated cells may have produced VSV particles with low infectivity, which may be related to the reduced amount of glycoprotein incorporated into such particles. These findings resemble those reported in interferon-treated cells infected with murine leukemia viruses.

Induction of simian virus 40-specific tumour rejection by the Ad2+ND2 hybrid virus

Immunization of BALB/c mice with Ad2+ND2, a non-defective hybrid virus containing about half of the early region of simian virus 40 (SV40) DNA covalently integrated into the human adenovirus 2 (Ad2) genome, can confer protection against subsequent challenge by syngeneic SV40 tumour cells. Analysis of subcellular fractions from Ad2+ND2-infected cells shows a close correlation between the tumour rejection activity and the presence of the two SV40-specific proteins induced by this hybrid virus. These two proteins, with mol. wt. of 56 000 (56K) and 42 000 (42K), can be specifically immunoprecipitated using sera obtained from hamsters bearing SV40-induced tumours. Such immunoprecipitates, which contain no detectable contaminating components as determined by polyacrylamide gel electrophoresis, can efficiently immunize mice against SV40 tumour challenge, suggesting that the 56K and 42K proteins are directly responsible for the induction of tumour rejection. Moreover, we have found, by immunoprecipitation, a novel antigen in SV40-transformed BALB/c cells, also of 56 000 mol. wt.; possibly, this 56K protein is responsible for induction of transplantation immunity in SV40-transformed cells.

Parvovirus RNA transcripts containing sequences not present in mature mRNA: a method for isolation of putative mRNA precursor sequences

We report here a method of RNA preparation that may enrich for precursor RNA sequences and the results of an investigation of adeno-associated virus (AAV) RNA transcription that used this method. Whole cells were lysed with detergent and high salt and separated into supernatant and pellet (crude chromatin) fractions. These fractions were then separately deproteinized by proteolytic digestion and phenol extractions. DNA was removed from the preparation by two cycles of pancreatic DNase digestion and phenol extraction. Hybridization analyses of the RNA obtained from AAV/adenovirus-infected KB (human) cells revealed some AAV-specific RNA sequences that were not present in the mature 20S mRNA. These additional sequences were contained in AAV RNA molecules present in the pellet fraction, whereas the 20S AAV mRNA accumulated in the supernatant. A species of AAV-specific RNA (about 22S), which was associated only with the pellet fraction and was labeled only after a short pulse, appeared to have a kinetic relationship with the more stable cytoplasmic 20S mRNA. These putative AAV mRNA "precursors" and precursor sequences were not observed previously when conventional methods were used to obtain RNA from either whole cells or isolated nuclei.

Tumor-specific transplantation antigen: use of the Ad2+ND1 hybrid virus to identify the protein responsible for simian virus 40 tumor rejection and its genetic origin

Cells transformed by simian virus 40 (SV40) possess a tumor-specific transplantation antigen (TSTA) that has the property of immunizing animals against syngeneic tumor challenge. We find that the early SV40 DNA segment present in the human adenovirus 2 (Ad2)-SV40 hybrid, Ad2+ND1, is sufficient to induce this SV40-specific TSTA in BALB/c mice. Moreover, studies on the intracellular distribution of TSTA activity in Ad2+ND1-infected cells, as determined by the ability of various subcellular fractions to immunize mice against syngeneic tumor challenge, have suggested a correlation between this biological activity and the presence of the SV40-specific 28,000Mr protein in coded by this hybrid virus. Both the TSTA activity and the 28,000 Mr protein are found in the plasma membrane fraction and in the perinuclear region of infected cells but are virtually undetectable in the cytoplasmic fraction. Using a hamster antitumor antiserum that can specifically immunoprecipitate the 28,000 Mr protein, we are able to demonstrate a loss of TSTA activity concomitant with the removal of this SV40-coded protein. Thus, it appears that antigenic determinants responsible for SV40-specific tumor rejection in mice are contained within the 28,000 Mr protein coded for by the early SV40 DNA segment that extends from 0.17 to 0.28 map unit.

Biosynthesis, immunological specificity, and intracellular distribution of the simian virus 40-specific protein induced by the nondefective hybrid Ad2+ND1

Ad2(+)ND(1), a nondefective hybrid virus containing a segment of the early region of simian virus 40 (SV40) DNA covalently inserted into the human adenovirus 2 genome, enhances the growth of human adenoviruses in simian cells and induces the SV40 U antigen. This hybrid previously has been shown to code for a 28,000 (28K) molecular weight protein not present in wild-type adenovirus 2-infected cells. By radioimmunoprecipitation using sera from hamsters bearing SV40-specific tumors, we have established that the Ad2(+)ND(1)-induced 28K protein is SV40-specific. This Ad2(+)ND(1)-induced protein is synthesized as a 30K molecular weight precursor, which is detectable only when infected cells are pulse-labeled in the presence of the protease inhibitor tosylamino phenylethyl chloromethyl ketone. Upon fractionation of labeled cell extracts, about 80% of the 28K protein is found in the plasma membrane fraction, whereas the remaining 20% is associated with the outer nuclear membrane. This protein is not detectable either in the nucleus or in the cytoplasm. Blockage of proteolytic cleavage by tosylamino phenylethyl chloromethyl ketone did not alter the topographic distribution of this SV40-specific protein, although the amount of the precursor protein in the outer nuclear membrane increased fourfold while that in the plasma membrane was proportionately decreased. This result suggests that the 28K protein is transferred from the outer nuclear membrane to the plasma membrane after posttranslational cleavage of the 30K precursor polypeptide. These data offer further support to the proposal that the 28K protein contains the determinants for SV40 U antigen and is responsible for SV40 enhancement of adenovirus growth in simian cells.

Physical, morphological, and biochemical alterations in the membrane of AKR mouse cells after interferon treatment

Interferon treatment of AKR,C- cells was followed by the establishment of an antiviral state and apparently concomitant morphological, physical, and biochemical alterations of the cell plasma membrane. The density of the plasma membrane was significant altered, and the concentration of some plasma membrane glycoproteins and the number of intramembranous particles observed in freeze-fracture electron micrographs were increased. A parallel increase in the concentration of intramembranous particles and the resistance to viral infection during interferon treatment as well as their parallel decrease upon removal of interferon suggests a relationship between the particle density and the establishment of the antiviral state.

Identification of a transformation-specific protein induced by a Rous sarcoma virus

Using antisera obtained from rats bearing Schmidt-Ruppin strain Rous sarcoma virus-induced tumors, we have idnetified a protein with an apparent molecular weight of 56,000 daltons and an isoelectric point of 6.3 in extracts of chick embryo fibroblasts transformed by a wild-type nondefective Rous sarcoma virus (Schmidt-Ruppin strain). This protein was not found in cells infected by trnasformation-defective mutants with either a partial or complete deletion of the src gene, nor in cells infected by a nontransforming avian leukosis virus. The 56,000 dalton molecular weight protein was found to be synthesized at both the permissive and nonpermissive temperatures in cells infected by either of two conditionallethal mutants that are temperature-sensitive in cell transformation. The amount of this protein, however, accumulated in cells infected by these temperature-sensitive mutants, relative to the structural polypeptides, differed significnatly from that seen with the nondefective virus. Pulsechase experiments indicate that the protein is extremely unstable, with a half-life of about 20 min, and does not serve as a precursor to any of the detectable virion polypeptides. Furthermore, incubation of the rat antiserum with purified, disrupted virus did not affect its immunoreactivity to this particular protein. We conclude that this 56,000 dalton molecular weight protein is a nonstructural protein specific to cells transformed by Rous sarcoma virus.

Membrane alterations following interferon treatment

Interferon treatment appears to induce a number of changes in the plasma membrane of uninfected cells. Interferon treatment altered the surface exposure of gangliosides of both Ly and KB cell membranes. The differences were found in the amount and pattern of incorporation of tritium after galactose oxidase treatment. In AKR,C- (AKR-2B) mouse cells, not only was there an apparent increase in the number of intramembranous particles in response to treatment with interferon but also the kinetics of the increase followed that of the establishment of the antiviral activity. The buoyant density of plasma membrane was also found to be significantly increased in interferon-treated cells. Moloney murine leukemia virus produced in interferon-treated mouse thymus and bone marrow cells had a high particle to infectivity ration. This virus contained a prominent glycoprotein with a molecular weight of about 85,000. This large glycoprotein was only a very minor component of Moloney leukemia virus produced in control TB cells and might be an uncleaved precursor to gp 69-71.

Simian virus 40-specific ribosome-binding proteins induced by a nondefective adenovirus 2-simian virus 40 hybrid

We have studied the intracellular distribution of the two simian virus 40-specific proteins, with apparent molecular weights of 56,000 and 42,000, detectable in human KB cells infected by a nondefective adenovirus 2-simian virus 40 hybrid, Ad2+ND2. After a 20-min pulse of [35S]methionine, about two-thirds of the newly synthesized 56K protein and one-third of the 42K protein were found localized on the plasma membrane. The remainder of each protein was found in the cytoplasm, whereas the nuclear fraction was virtually free of either component. A significant portion of both proteins present in the cytoplasmic fraction was complexed to the 40S ribosomal subunits and was not removed by treatment with 0.5 M KCl. Moreover, the portion that was found free in the cytoplasm could bind preferentially and quantitatively to purified 40S ribosomes in vitro, leading us to propose that these simian virus 40 proteins may act as translational control elements in cells.

The separation of ribonucleic acids from Escherichia coli on lysin-agarose

Lysine-agarose provides a simple means of separating RNA species of different moleecular weight. When RNA from Escherichia coli is added to a small column of lysine-agarose and elution is carried out at neutral pH with a shallow linear gradient of NaCl the RNA species are eluted according to size; 4S and 5S RNA species are completely separated and after a delay the 16S and 23S species are eluted as separate peaks. The process is very reproducible and the different species are eluted at a fixed salt concentration even when changes are made in the gradient, provided other conditions, under which the column is run remain constant.

Persistence of the viral genome in interferon-treated cells infected with oncogneic or nononcogenic viruses

In AKR mouse cells chronically infected with a murine leukemia virus, treatment with interferon for nine days resulted in sustained inhibition of extracellular production of murine leukemia virus but no inhibition of viral intracellular p30 antigen or of reverse transcriptase. Removal of interferon resulted in rapid reversal of these effects. Interferon-treated mouse L-cells were infected with high multiplicities of vesicular stomatitis virus or herpes simplex virus type 1. Infectious virus and intracellular viral antigen were rapidly eliminated from the interferon-treated cultures infected with herpes simplex virus. In cultures infected with vesicular stomatitis virus, titers of virus remained low in interferon-treated cells, but after about two weeks they rose rapidly and the cultures were destroyed. If treatment with interferon was reinstituted as late as nine days after primary infection, infectious vesicular stomatitis virus was eliminated, and there was no evidence for survival of the viral genome in these cultures. In the cultures infected with murine leukemia virus, inhibition of production of virus by treatment with interferon was possible, but the viral genome was not eliminated. In cells acutely infected with vesicular stomatitis virus or herpes simplex virus, however, the viral genomes were apparently eliminated from cultures treated with interferon.

The use of a dipolar ion-exchanger for the fractionation of transfer ribonucleic acid

Transfer ribonucleic acid is well fractionated on columns of arginine-agarose, whose properties appear in general to be similar to those of DEAE-Sephadex. However, the amino acid acceptor species are separated into sharper peaks and in several instances, notably for methionine, glycine, serine, leucine and aspartate accepting tRNAs from Escherichia coli, isoaccepting species are well resolved. In the case of methionine accepting tRNA from E. coli the tRNA Met-m species is eluted before the tRNA Met-f species and since it is also eluted prior to the bulk of the tRNA it is obtained in a high degree of purity. By comparing the properties of columns of arginine-agarose and its methyl ester in which the carboxylate anion is blocked, it is seen that the carboxylate ion plays a role in the fractionation of the tRNA Met species.