Effects of acute systemic treatment with the 5 HT-uptake blocker alaproclate on tissue levels and release of substance P in rat periaqueductal grey

The effects of acute systemic treatment with alaproclate, a serotonin uptake blocker on regional brain tissue levels of substance P, neurokinin A and cholecystokinin were studied in the rat. The peptide levels of all three peptides were increased (23-35%) in the rat periaqueductal grey 60 min after treatment with alaproclate (20 mumol/kg peroral, p.o.), compared to controls. In the cingulate cortex, the tissue levels of substance P and cholecystokinin were increased (19-32%) after subcutaneous (s.c.) treatment with alaproclate, compared to controls. Higher tissue levels of all three peptides (20-38%) in the periaqueductal grey, and lower levels of substance P and cholecystokinin in the cingulate cortex were found following saline s.c. compared to saline p.o., probably due to different degrees of stress. In microdialysis experiments, a s.c. injection of either saline (2 ml/kg), alaproclate (20 mumol/kg) or morphine (3 mg/kg) was found to slowly increase the substance P release in the periaqueductal grey. Experiments with the selective 5-HT neurotoxin, 5,7-dihydroxytryptamine indicated no neuronal co-existence of substance P and serotonin in the periaqueductal grey and cingulate cortex. In conclusion, acute treatment with the serotonin uptake blocker alaproclate increases both the tissue level and the release of substance P in the periaqueductal grey.

Genomic organization and complete cDNA sequence of the human phosphoinositide-specific phospholipase C beta 3 gene (PLCB3)

We have characterized the complete cDNA sequence, genomic structure, and expression of the human phosphoinositide-specific phospholipase C beta 3 (PLC beta 3) gene (gene symbol PLCB3). PLC beta 3 plays an important role in initiating receptor-mediated signal transduction. Activation of PLC takes place in many cells as a response to stimulation by hormones, growth factors, neurotransmitters, and other ligands. The partial cDNA sequence of PLC beta 3, previously published, was extended with 876 bp in the 5' direction, giving a transcript of 4400 bp and a total open reading frame of 1234 amino acids. This was in accordance with expression analysis by Northern blotting that revealed a single 4.4-kb transcript in all tissues tested. Genomic data were obtained by sequencing plasmid subclones of a cosmid that contained the whole gene. The size of the complete transcription unit was estimated to be on the order of 15 kb. The gene contains 31 exons, with all splice donor and acceptor sites conforming to the GT/AG rule. No exon exceeds 571 bp in length, and the shortest exon spans only 36 bp. More than half of the introns are smaller than 200 bp, with the smallest being only 79 bp long. The transcription initiation site was determined to be within an 8-bp cluster 328-321 bp upstream of the translation initiation site. The 5'flanking region is highly GC rich, with multiple CpG doublets, and contains multiple binding sites for Sp1. Lacking typical transcriptional regulatory sequences such as TATA and CAAT boxes, the putative promoter region conforms to the group of housekeeping promoters.

EBV infection of B-CLL cells in vitro potentiates their allostimulatory capacity if accompanied by acquisition of the activated phenotype

Epstein-Barr virus (EBV)-carrying immortalized lymphoblastoid cell lines (LCLs) stimulate autologous T lymphocytes in vitro. This T-cell response is independent of the EBV-specific cellular memory because it also occurs in experiments with cells of seronegative individuals. The question can be posed whether the T-cell-stimulatory potential of the LCL is coupled to its immortalized state. B-CLL cells were exploited to study this question because the majority of clones, represented by different patients, can be infected with EBV but they rarely become immortalized. We have investigated the phenotypic changes and the T-cell-stimulatory capacity of EBV-infected B-CLL cells. One aliquot of CLL cells was infected with EBV, another was activated with a mixture of Staphylococcus aureus (SAC), IL-2 and the supernatant from the T-cell hybridoma MP6 (activation mixture, AcMx) and the third aliquot received both treatments. In accordance with the individual features of the clonal populations represented by each patient, the immunophenotypic changes imposed by these treatments differed. With the samples of 3 patients the allo-stimulatory potential showed the following ranking order: EBV and AcMx-treated cells > AcMx-treated > EBV-infected. An analysis of several activation-related surface markers and adhesion molecules on the cells did not reveal any association between their expression and the EBV-imposed potentiation of allostimulatory capacity. These results may be extrapolated to EBV-genome-carrying normal B cells, suggesting that they can persist in vivo only as long as they have the resting phenotype. Once they are activated, these cells may be recognized and eliminated by T lymphocytes.

Multiple molecular forms of tachykinins in rat spinal cord: a study comparing different extraction methods

Various procedures for extraction at acid, neutral and alkaline pH were compared with regard to the yield of different tachykinins and tachykinin-like substances from rat spinal cord. Reverse phase high performance liquid chromatography (RP-HPLC) and radioimmunoassay with various C-terminally directed tachykinin antisera and a newly developed N-terminally directed substance P (SP)-antiserum (SPN 1) were used. Antiserum SPN 1 fully reacts with SP-analogues modified at the C-terminal end (SP free acid and SP-Gly-Lys) and also (77%) with SP(1-9) but not with C-terminal SP-fragments lacking 2 or more N-terminal amino acids. The highest levels of SP-like immunoreactivity (LI) and neurokinin A (NKA)-LI were measured after combined water and acetic acid extraction procedures. Also when measuring cholecystokinin-like immunoreactivity the highest level was obtained following this extraction procedure. RP-HPLC revealed a major component of SP-LI at the position of synthetic SP irrespectively of the extraction method and if the C- or N-terminally directed antiserum was used. Neutral water extracts contained a late eluting component detected with the C-terminally, but not with the N-terminally, directed antiserum. Acid and alkaline extracts, in contrast, contained components which could be detected with the N-terminally, but not with the C-terminally, directed SP-antiserum. Immunoreactive components eluting at the position of NKA and NKB were found in all types of extracts with NKA-, kassinin- and eledoisin-antisera. The NKB- and neuropeptide K (NPK)-components were more prominent in acid than in neutral and alkaline extracts. In conclusion, the present results indicate that rat spinal cord may contain molecular forms of tachykinin-like immunoreactivity in addition to those previously described and illustrate the importance of the choice of extraction method in immunochemical studies. Combined extraction in water and acetic acid appears to be a suitable method when the content of peptides with different chemical properties are to be measured in a tissue sample.

Effects of sequential removal of rats from a group cage, and of individual housing of rats, on substance P, cholecystokinin and somatostatin levels in the periaqueductal grey and limbic regions

The effect of specific stressful stimuli on neuropeptide levels was studied in rat brain regions known to be involved in the mediation of stress responses and anxiety. Rats were sequentially removed, one by one with 20-min intervals from group cages and immediately decapitated. A selective increase of the somatostatin level was observed in the amygdala in the rats taken for sacrifice second last and last, compared to the rats taken earlier from the respective group cage (increases by 40 to 69%, p < 0.05 or p < 0.01). Isolation of rats in single cages for 24 h or 1 week before sacrifice, increased the substance P level in the dorsal periaqueductal grey by 26 and 27% (p < 0.05 in both cases), respectively, compared to group housed rats. In group housed rats treated with diazepam (5 mg/kg, s.c.) 140 min before sacrifice, the level of substance P in the rostral hippocampus and dorsal periaqueductal grey was reduced by 40% (p < 0.001) and 28% (p < 0.05), respectively, compared to saline treated controls. In conclusion, handling, as well as a single dose of the anxiolytic drug diazepam, appears to induce rapid, selective and region-specific changes of regional brain peptide levels in the rat. The effects of handling are likely to be related to the acute stress response and are probably not secondary to increased plasma glucocorticoid levels.

Epstein-Barr virus (EBV) can immortalize B-cll cells activated by cytokines

B-type of chronic lymphocytic leukemia (B-CLL) cells are inert to the potent transforming action of Epstein-Barr virus (EBV). The mitogenic action of Staphylococcus aureus Cowan I (SAC), MP6-thioredoxin, and interleukin 2 (IL-2), agents previously shown to induce proliferation in normal as well as in B-CLL cells, lifted this block, and EBV-positive cell lines could be established. It was not possible to establish cell lines of leukemic origin from cultures that were incubated with EBV alone or cytokine mix alone. CLL-cells infected with EBV only, expressed the viral nuclear antigen complex (EBNA), but not the viral latent membrane protein (LMP). They were not activated as measured by cell size and 3H-thymidine incorporation. In contrast, cells incubated with EBV and cytokine mix expressed both EBNA and LMP in parallel with enlargement and increased 3H-thymidine incorporation. These results emphasize that LMP expression is a prerequisite for growth transformation and immortalization and that cytokine activation signals are required for its expression in B-CLLs. Cells incubated with SAC/MP6-thioredoxin/IL-2 did not express any of the viral antigens, but were activated with regard to the mentioned parameters. Nine cell lines were established from six patients. From each of the three patients, we obtained 'twin'-pair lines: one corresponding to the malignant cell and the other to a normal B-lymphoblastoid cell. Thus, malignant and normal B-cell counterparts, from the very same donor, are at hand for comparative studies. The cell lines have been carried out for more than 12 months in culture. We conclude that B-CLL that are refractory to EBV-transformation can be rendered susceptible through in vitro cytokine activation.

Higher proliferative response in B-chronic lymphocytic leukemia (B-CLL) as compared to B-monoclonal lymphocytosis of undetermined significance (B-MLUS) after stimulation with Staphylococcus aureus and anti-CD40 monoclonal antibodies

B-CLL is a malignant monoclonal B-cell disorder and B-MLUS is the benign counterpart. The proliferative response and the capacity to secrete IgM was measured in B-CLL and B-MLUS, respectively, and compared to normal B-cells. SAC and a mAb against CD40 were used as stimulatory agents. No cell population responded to anti-CD40 mAb alone. SAC only induced a high DNA synthesis rate in normal B-cells as well as in B-CLL cells, although the magnitude was three-fold lower and delayed for about 48 h in B-CLL. B-MLUS cells did not proliferate in response to SAC. The combination of anti-CD40 and SAC enhanced the proliferative capacity of normal B-cells and produced a more rapid response in B-CLL. B-MLUS cells were not activated. Normal B-cells and B-MLUS did not secrete IgM after SAC stimulation, while B-CLL cells had a continuous increase in the IgM production during a 6-day culture period. The higher proliferative capacity of B-CLL cells compared with B-MLUS cells may be explained by an increased expression of activation molecules e.g. receptors for various cytokines and growth factors. Moreover, the inertness and inability of B-MLUS cells in comparison to normal B- and B-CLL cells to respond to powerful activation signals might indicate an intrinsic defect of B-MLUS cells in the signal transduction leading to a block of mitosis and a benign course of the disease.

Monoclonal antibody against a lactose epitope of glycosphingolipids binds to melanoma tumour cells

Mice were immunized with a neoglycoprotein consisting of a chemically modified carbohydrate moiety (reductively aminated 3'-sialyllactose) linked to human serum albumin. By this procedure an antibody response to the normally non-immunogenic carbohydrate structure was obtained. Hybridomas were established, and monoclonal antibodies were selected in ELISA based on their binding to the saccharide hapten, or to a lactosylceramide-mimicking neoglycolipid, lactose-bis-sulfone. One of the selected antibodies, 2H4, was of particular interest, since it also bound to glycolipids present on melanoma cells. FACS analysis of a panel of 14 melanoma cell lines showed that the 2H4 antibody bound to the majority of these. In frozen, non-fixed sections or paraffin sections of biopsies the monoclonal antibody 2H4 stained melanoma cells, but not tumour infiltrating lymphocytes or normal skin. Detailed immunochemical analysis of 2H4, using thin layer chromatography revealed that it recognized an internal lactose epitope in several glycosphingolipids.

CD23 and CD21 function as adhesion molecules in homotypic aggregation of human B lymphocytes

We have previously found that interleukin-4 and CD40 monoclonal antibodies (mAb) are strong potentiators of homotypic B cell aggregation which is dependent on LFA-1. We show here that CD23 mAb were also able to inhibit aggregation to a similar extent as LFA-1 antibodies. This inhibition was restricted to the MHM6 epitope of CD23 and antibodies to other epitopes [Epstein-Barr virus (EBV) CS-1, EBV CS-2, EBV CS-5 and mAb 25] or occupation of the Fc-binding site by IgE had no or a slightly enhancing effect on aggregation. When testing two antibodies to CD21, the recently defined ligand for CD23, one of these (BU32) was found to be inhibitory whereas the other (THB5) had no effect. By combining antibodies to LFA-1 and CD23, aggregation was often completely inhibited. These data suggest that LFA-1/ICAM-1 and CD23/CD21 are the major molecules involved in homotypic aggregation of human B cells.

Neutralizing human monoclonal antibodies against Puumala virus, causative agent of nephropathia epidemica: a novel method using antigen-coated magnetic beads for specific B cell isolation

Human monoclonal antibodies (MAbs) against Puumala (PUU) virus were generated and characterized. Human spleen B lymphocytes were preselected for specific surface immunoglobulin (Ig) using magnetic beads coated with the viral glycoproteins, and subsequently immortalized by Epstein-Barr virus transformation. Four IgG-positive monoclonal lymphoblastoid cell lines (LCLs) were established and have remained stable MAb secretors for over 12 months. Analyses of the antigen and epitope specificities recognized by the MAbs showed overlapping binding patterns of four anti-glycoprotein 2-specific clones. Identical isotypes (IgGl lambda) and isoelectric points (9.2) of the four MAbs suggested that they were derived from the same original clone. The MAbs reacted with eight PUU virus-like strains, but were negative for Hantaan, Seoul, and Prospect Hill viruses in an immunofluorescence assay, indicating binding to a conserved epitope unique for strains associated with the European form of haemorrhagic fever with renal syndrome, nephropathia epidemica. The MAbs neutralized all investigated PUU virus-like strains in a focus reduction neutralization test. The MAb neutralizing activity was significantly enhanced in the presence of human or guinea-pig complement. To stabilize and increase antibody secretion and to reduce the demand for culture medium supplements (e.g. fetal calf serum), three of the monoclonal LCLs were fused with the non-secreting human x mouse partner SPAM-8. Several of the established human x (human x mouse) monoclonal triomas grew faster and produced larger amounts of MAbs when compared with the original LCLs.

Position-dependent nuclear accumulation of the retinoblastoma (RB) protein during in vitro myogenesis

The expression of the retinoblastoma (RB) protein has been studied during in vitro muscle differentiation by immunofluorescence staining with three different antibodies against RB protein. Proliferating mononucleate L6 rat myoblasts showed a low level of expression. As cells began to enter a nonreplicating G0 state, the cell population became heterogeneous. Some nonreplicating cells showed a high level of expression. Nuclei at the two ends of myotubes were strongly positive, whereas centrally located nuclei showed low RB expression. Overexpression of the human RB protein in rat L6 myotubes from a Semliki forest virus (SFV)-based, transient expression vector produced a similar picture. Terminally located nuclei expressed human RB at a much higher level than did the centrally located nuclei. The results suggest that individual nuclei with a multinucleated syncytium may undergo position-dependent specialization.

Double-blind trial of aspirin in primary prevention of myocardial infarction in patients with stable chronic angina pectoris. The Swedish Angina Pectoris Aspirin Trial (SAPAT) Group

Clinical trials have demonstrated a prophylactic role for aspirin in myocardial infarction and in unstable angina pectoris. The Swedish Angina Pectoris Aspirin Trial (SAPAT) is the first prospective study of aspirin in stable angina. 2035 patients were randomised double-blind to treatment with aspirin 75 mg daily or placebo. All patients were treated with sotalol for control of symptoms. The median duration of follow-up was 50 months. Compared with the placebo+sotalol group, the aspirin+sotalol group had a 34% (81 vs 124 patients) reduction in primary outcome events (myocardial infarction and sudden death; 95% confidence interval 24-49%; p = 0.003) and the reduction observed in secondary outcome events (vascular events, vascular death, all cause mortality, stroke) ranged from 22% to 32%. Treatment withdrawal caused by adverse events occurred in 109 patients in the aspirin+sotalol group and 100 in patients in the placebo+sotalol group; major bleeds, including haemorrhagic stroke, occurred in 20 and 13 patients, respectively (not significant). The addition of a low dose of aspirin to sotalol treatment showed significant benefit in terms of cardiovascular events, including a significant reduction in the incidence of first myocardial infarction in patients with symptoms of stable angina pectoris.

Anti-GM3-lactam monoclonal antibodies of the IgG type recognize natural GM3-ganglioside lactone but not GM3-ganglioside

Immunization of mice with a synthetic GM3-lactam-BSA (bovine serum albumin) conjugate (designed to emulate the corresponding natural GM3-lactone conjugate), followed by fusion of splenocytes with myeloma cells, gave rise to more than 300 monoclonal hybridomas producing antibodies to GM3-lactam-BSA, which did not react with Glc-BSA and BSA. Eight antibody clones were randomly chosen from the positive 300 hybridomas. The eight clones, all belonging to the IgG class, were unreactive against GM3-ganglioside, whereas two antibodies (P5-1 and P5-3, both IgG1, kappa) reacted with GM3-ganglioside lactone. Binding of these two antibodies to the GM3-lactam-BSA conjugate was inhibited by soluble glycosides of GM2-, GM3-, and GM4-lactam and by GM3- and GM4-lactam, respectively, but not by Gb3 or asialo-GM1 and GM2-saccharides. A third antibody (P3; IgG2b, kappa) was inhibited by GM2-, GM3-, and GM4-lactam, but did not recognize GM3-ganglioside lactone.

Short-term restraint stress and s.c. saline injection alter the tissue levels of substance P and cholecystokinin in the peri-aqueductal grey and limbic regions of rat brain

Rats were exposed to short-term restraint (held by the tail for 1 min), injected s.c. with saline or subjected to the combination of these treatments. Fifteen and 30 min after these treatments the means serum corticosterone level was significantly increased by more than four times, compared to rats taken directly from their home cages, indicating a stress response. In the peri-aqueductal grey, the level of substance P-like immunoreactivity was increased by 45% (P < 0.01) and 65% (P < 0.01) 30 and 60 min after the combined treatment, respectively. Significant increases of the level of substance P-like immunoreactivity in the peri-aqueductal grey were also found after restraint only and after a s.c. saline injection. Similar, but less marked, changes in the level of cholecystokinin-like immunoreactivity in the PAG were also seen. In the accumbens a significantly decreased level of substance P-like immunoreactivity was encountered at 15 and 30 min after treatment, while the levels of cholecystokinin- and neuropeptide Y-like immunoreactivity were not significantly changed. In other regions studied, no effects on peptide levels were seen. The changes in peptide levels had a time course similar to that of the increase in serum corticosterone. Also the successive removal of rats from a common cage was found to increase significantly the serum corticosterone and the substance P-like immunoreactivity in the peri-aqueductal grey in the animals that were taken late in sequence from the cage.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretion of thioredoxin after in vitro activation of human B cells

The redox-active enzyme thioredoxin (Trx) is secreted by various virus-transformed cell lines of B- and T-cell origin and has been considered to play an autoregulatory role as a cofactor during cellular growth processes. We show in this paper that exposure of B lymphocytes from normal, healthy donors and B cells from B-type chronic lymphocytic leukemia (B-CLL) to Staphylococcus aureus Cowan I (SAC) induced expression of Trx mRNA. By combining SAC, or the phorbol ester TPA, with IL-2 and the conditioned medium of a T-cell hybridoma (BSF-MP6), we could strongly enhance the Trx expression. After [35S]methionine labeling of stimulated B-CLL cells in vitro, Trx was immunoprecipitated both from cell extracts and from the medium with antibodies against human placenta Trx. Secretion of newly synthesized Trx was also confirmed by a quantitative radioimmunoassay for human Trx. During 24 h cultivation experiments, treatment with SAC induced a 5-fold increase of the Trx content of normal B lymphocytes as well as in B-CLL cells. Approximately two-thirds of the total amount of the enzyme was released into the medium.

Transcription of unrearranged Ig H chain genes in human B cell malignancies. Biased expression of genes encoded within the first duplication unit of the Ig H chain locus

Analysis of the H chain class switch recombination events on the productive and nonproductive alleles of several human B cell lines has demonstrated that, in the majority of cases, the two loci had rearranged different CH genes. The absence of a strict correlation between the two rearrangement events has been interpreted in favor of a stochastic switching mechanism in human B cells. Based on the accessibility model for the H chain class switch, we have considered an alternative explanation, namely, that transcriptional activation of more than one CH gene could render more than one isotype accessible for recombination. In order to test this possibility, we have stimulated a number of IgM-bearing B cell tumors and analyzed the transcriptional response of their unrearranged C gamma and C alpha H chain genes at the Ig class level by Northern hybridization and at the subclass level by RNA-RNA solution hybridization. Our data show that human clonal B cell populations can simultaneously express germ-line transcripts of both gamma and alpha genes. Our data also demonstrate a bias in the expression of the different isotypes in the B cell chronic lymphocytic leukemias analyzed, with the genes present with the first duplication unit of the H chain locus (gamma 3, gamma 1, and alpha 1) being expressed almost exclusively. These findings indicate that transcriptional activation of large chromosomal regions containing more than one CH gene could render all the genes available for recombination and, therefore, provide an explanation for the asymmetry in the rearrangement events that have previously been described in human B cell tumors. The possible relevance of our findings to the molecular mechanism of the H chain class switch is discussed.

Transcription of unrearranged Ig H chain genes in human B cell malignancies. Biased expression of genes encoded within the first duplication unit of the Ig H chain locus

Analysis of the H chain class switch recombination events on the productive and nonproductive alleles of several human B cell lines has demonstrated that, in the majority of cases, the two loci had rearranged different CH genes. The absence of a strict correlation between the two rearrangement events has been interpreted in favor of a stochastic switching mechanism in human B cells. Based on the accessibility model for the H chain class switch, we have considered an alternative explanation, namely, that transcriptional activation of more than one CH gene could render more than one isotype accessible for recombination. In order to test this possibility, we have stimulated a number of IgM-bearing B cell tumors and analyzed the transcriptional response of their unrearranged C gamma and C alpha H chain genes at the Ig class level by Northern hybridization and at the subclass level by RNA-RNA solution hybridization. Our data show that human clonal B cell populations can simultaneously express germ-line transcripts of both gamma and alpha genes. Our data also demonstrate a bias in the expression of the different isotypes in the B cell chronic lymphocytic leukemias analyzed, with the genes present with the first duplication unit of the H chain locus (gamma 3, gamma 1, and alpha 1) being expressed almost exclusively. These findings indicate that transcriptional activation of large chromosomal regions containing more than one CH gene could render all the genes available for recombination and, therefore, provide an explanation for the asymmetry in the rearrangement events that have previously been described in human B cell tumors. The possible relevance of our findings to the molecular mechanism of the H chain class switch is discussed.

Cell phenotype (CD23)-dependent variation in EBV genome copy numbers within lymphoblastoid cell lines (LCL)

Three Epstein-Barr-virus-transformed lymphoblastoid cell lines (LCL) were analysed on the basis of their CD23 expression. Levels of EBV-DNA were compared in the positive and negative subpopulations. Two lines were further analysed with regard to EBNA, cytoplasmic immunoglobulin (cIg) and lytic (EA/VCA) protein expression. Both subpopulations had a similar MHC class-II transcription, but the CD23- subpopulation had a lower plating efficiency and a lower rate of DNA synthesis. In the B6, NAD50 and 0467.3 cell lines, CD23- cells contained 2 +/- 0.2 - 6.4 +/- 3.0 times less EBV DNA than the corresponding CD23+ population. EBNA was expressed in 81 +/- 4.2% - 93 +/- 3.8% of the CD23+ cells and in 0 - 46 +/- 8.0% of the CD23- cells. No CD23+ cells in B6 or NAD50 contained any EA/VCA, while 19 +/- 2.8% - 24 +/- 4.2% of the CD23- cells were positive for the lytic-cycle-associated antigens. Of the CD23- cells, 70 +/- 8.6% - 86 +/- 6.0% were positive for cytoplasmic immunoglobulin compared to 14.7 +/- 2.7% - 14.9 +/- 1.8% in the corresponding CD23+ population. We have previously shown that only 18% of the cIg-positive cells were EBNA-positive in the B6 line compared to 94% in the cIg- population. This was open to 2 alternative interpretations: loss of EBV genomes from a fraction of the cells with subsequent differentiation to secretory immunoglobulin production, or down-regulation of EBNA expression in differentiating, EBV-genome-positive cells. Our present findings speak for the first alternative, indicating that a certain proportion of the cells may lose their EBV genomes in both long-established and freshly transformed LCLs. This is accompanied by a reduced percentage of EBNA-positive cells, the disappearance of at least one activation marker (CD23) associated with the virally induced blast transformation, and an increased synthesis of cIg.

Co-localization of the retinoblastoma protein and the Epstein-Barr virus-encoded nuclear antigen EBNA-5

A monoclonal antibody (aRB1C1) raised against an Rb fusion protein detects a limited number (4-10) of relatively large intranuclear foci in an EBV-immortalized cord blood cell line (IB4). These domains also bind an anti-EBNA-5 monoclonal antibody. The Rb antibody reactive sites also co-localize with the SV40 T antigen in transformed monkey cells (COS). The nuclear structures stained by aRB1C1 and EBNA-5 antibodies are distinct from the structures detected with antibodies against centromeric proteins and certain snRNP epitopes. EBNA-5/Rb-positive domains do not selectively react with antibodies against the La antigen known to associate with the small EBV-encoded nuclear RNA species designated as the EBERs.