YAC-1 MHC class I variants reveal an association between decreased NK sensitivity and increased H-2 expression after interferon treatment or in vivo passage

Two H-2 negative variants of the YAC-1 lymphoma were selected by mutagenization and sequential in vitro selections and compared with wild-type cells for changes in NK sensitivity and H-2 expression after interferon treatment or in vivo passage. The H-2 negative variants and the low H-2 expressor YAC-1 wild-type cells had similar NK sensitivity. However, IFN-beta or recombinant IFN-gamma pretreatments increased the H-2 expression of YAC-1 and protected them from NK lysis, whereas the H-2 variants, which remained H-2 negative, were not protected and often more sensitive to NK lysis. The H-2 variants were similarly susceptible as wild-type cells to three other cellular effects of interferon: protection from virus infection, modulation of Con A capping, and inhibition of cell proliferation. Thus, the only interferon-mediated effect that distinguished the H-2 negative variants from wild-type cells was the inability of the former to increase their H-2 expression and decrease their NK sensitivity. The wild-type YAC-1 line showed increased H-2 expression and decreased NK sensitivity after in vivo passage. In contrast, in vivo passaged H-2 variants showed no reexpression of H-2, and remained NK sensitive. The altered responses to interferon and in vivo passage were specific for loss or down-regulation of H-2, because Thy-1 loss (H-2 positive) YAC-1 variants behaved as the wild-type cells in all respects. This study supports the hypothesis that NK cells may function in vivo to eliminate host cells that fail to express H-2 after interferon stimulation during an immune response; such cells are a potential threat because they may escape recognition by T lymphocytes despite the expression of viral or tumor-associated antigens.

Cellular and viral DNA hypomethylation associated with induction of Epstein-Barr virus lytic cycle

Epstein-Barr virus (EBV) producer and nonproducer cell lines have been treated with a combination of phorbol 12-myristate 13-acetate and n-butyrate (sodium salt). These inducers caused a massive hypomethylation of the EBV producer line P3HR-1 DNA (about 30%) at the time when DNA replication was inhibited. The viral DNA in these cells is heavily methylated as judged by digestion with Hpa II and probing with the Bam HI H fragment of EBV. However, upon induction with phorbol 12-myristate 13-acetate and n-butyrate, total hypomethylation of this viral DNA region was observed within 24 hr. This hypomethylation preceded EBV amplification, which became apparent only 32-36 hr after induction. When induction was carried out in the presence of retinoic acid, hypomethylation of cellular and viral DNA, viral DNA amplification, and production of the viral early antigen and viral capsid antigen were substantially inhibited. EBV DNA in another producer line (Jijoye nude) and in the nonproducer line Raji was hypomethylated and did not undergo further hypomethylation in response to induction. The observed hypomethylation of P3HR-1 and EBV DNA in the absence of DNA replication suggests that it is achieved by an active demethylation mechanism. This changes our perception of the DNA methylation phenomenon, since it has been generally accepted that hypomethylation of DNA takes place by a passive mechanism that involves DNA replication in the absence of methylation.

YAC-1 MHC class I variants reveal an association between decreased NK sensitivity and increased H-2 expression after interferon treatment or in vivo passage

Two H-2 negative variants of the YAC-1 lymphoma were selected by mutagenization and sequential in vitro selections and compared with wild-type cells for changes in NK sensitivity and H-2 expression after interferon treatment or in vivo passage. The H-2 negative variants and the low H-2 expressor YAC-1 wild-type cells had similar NK sensitivity. However, IFN-beta or recombinant IFN-gamma pretreatments increased the H-2 expression of YAC-1 and protected them from NK lysis, whereas the H-2 variants, which remained H-2 negative, were not protected and often more sensitive to NK lysis. The H-2 variants were similarly susceptible as wild-type cells to three other cellular effects of interferon: protection from virus infection, modulation of Con A capping, and inhibition of cell proliferation. Thus, the only interferon-mediated effect that distinguished the H-2 negative variants from wild-type cells was the inability of the former to increase their H-2 expression and decrease their NK sensitivity. The wild-type YAC-1 line showed increased H-2 expression and decreased NK sensitivity after in vivo passage. In contrast, in vivo passaged H-2 variants showed no reexpression of H-2, and remained NK sensitive. The altered responses to interferon and in vivo passage were specific for loss or down-regulation of H-2, because Thy-1 loss (H-2 positive) YAC-1 variants behaved as the wild-type cells in all respects. This study supports the hypothesis that NK cells may function in vivo to eliminate host cells that fail to express H-2 after interferon stimulation during an immune response; such cells are a potential threat because they may escape recognition by T lymphocytes despite the expression of viral or tumor-associated antigens.

Mapping of the c-myc, pvt-1 and immunoglobulin kappa genes in relation to the mouse plasmacytoma-associated variant (6;15) translocation breakpoint

A variant mouse plasmacytoma (MPC)-associated translocation chromosome has arisen by pericentric inversion and exchange of the distal segments of a Robertsonian 6;15 fusion chromosome in the CAK TEPC 1198 mouse plasmacytoma, as described earlier. In situ hybridization was performed on the normal and the inverted Rb chromosomes, using myc and kappa probes. On the normal Rb chromosome, myc was in the 15 D2/3 region, whereas kappa hybridized in the 6 C2 area, as expected. On the inverted Rb chromosome, myc remains on the centrometric side of the translocation breakpoint on the chromosome 15-derived portion, whereas kappa has moved to the chromosome 6-derived segment that joined the same breakpoint on the telomeric side. Taken together with our recent demonstration that the murine c-myc locus is oriented 'head up' on chromosome 15, and with the results of Cory and co-workers concerning the relationship between the kappa gene and the associated pvt-1 region in the CAK TEPC 1198 tumor, the following conclusions can be drawn: (i) in the variant translocation of the CAK TEPC 1198 MPC, the breakage occurs 3' of the c-myc gene, as in the human Burkitt lymphoma-associated variant translocations; (ii) the pvt-1 gene on chromosome 15 is distal to the myc gene; (iii) the kappa light chain locus is oriented 'head up' on mouse chromosome 6 and faces pvt-1 and, beyond it, c-myc, in a head-to-tail configuration.

Lung colonization and metastasis by disseminated B16 melanoma cells: H-2 associated control at the level of the host and the tumor cell

We have studied the experimental metastasis of H-2+ and H-2- melanoma sublines in H-2b/b and H-2a/b hosts by enumerating pulmonary colonies 20-50 days after i.v. inoculation of tumor cells. In H-2b/b hosts, the H-2+ "B16-S" cells gave rise to a moderate number of metastatic colonies (mean: 6.3 +/- 6). The "BL16-L" sublines that had lost the expression of MHC class-I antigens, according to FACS-analysis and quantitative absorption tests, gave no metastases under the same conditions. Pretreatment of the H-2+ met+ B16-S with interferons (beta or alpha + beta) increased their H-2 antigen expression and the number of metastatic colonies (mean: 25 +/- 16). Interferon pretreatment of B16-L cells partially restored their H-2b expression and induced them to form a small number of metastatic colonies. The reduction in pulmonary colonization by the H-2 negative B16-L cells could be attributed to their rapid elimination by natural killer cells, already observed within 24 hr of inoculation of radiolabelled cells. H-2- B16-L cells were more susceptible than H-2+ B16-S cells to in vitro lysis by poly I:C-treated splenocytes, and they acquired full metastatic abilities if the hosts were treated with anti-asialo GM-I serum. In H-2a/b heterozygous hosts, the H-2+ B16-S cells also failed to metastasize. Reduced pulmonary colonization was evident by 24 hr after injection in comparison with H-2b/b hosts, and could be reversed by anti-asialo GM-I treatment of the hosts. In vitro, H-2a/b splenocytes were more cytotoxic to the B16 cells than syngeneic effectors. The results are discussed in relation to a recent hypothesis on a surveillance mechanism for elimination of cells on the basis of their lack (or insufficient expression) of host MHC genes.

Gene localization on sorted chromosomes: definitive evidence on the relative positioning of genes participating in the mouse plasmacytoma-associated typical translocation

Experiments have been carried out to establish the relative position of the mouse Ig heavy chain locus and the c-myc oncogene. In mouse plasmacytoma with the typical rcpt(12;15) chromosome translocation the c-myc oncogene is juxtaposed to one of the heavy chain genes in a head-to-head orientation. Since the relative orientations of the c-myc locus and the Ig heavy chain gene cluster on the corresponding mouse chromosomes had not been settled, it was not known whether the rearranged c-myc gene is transposed to chromosome 12 or remains on chromosome 15. To decide which of the two alternatives is correct, we separated the translocation chromosomes by fluorescence-activated chromosome sorting. The separated chromosomal fractions were hybridized with myc-specific DNA probes corresponding to the first or second/third exons in a chromosome spot assay. The results presented here indicate that the c-myc gene in mouse plasmacytoma carrying the typical translocation, as in the human Burkitt lymphoma analogous translocation, transposes to the chromosome carrying the Ig heavy chain locus. These results also establish the orientations of the Ig heavy chain locus and the c-myc locus on their normal chromosomes.

Surface marker characterization of EBV target cells in normal blood and tonsil B lymphocyte populations

Human FACS-sorted B lymphocyte subpopulations were investigated for their susceptibility to immortalization by Epstein Barr virus (EBV). Only B cells reacting with the monoclonal antibody B2 were immortalized, whereas cells reacting with anti-human IgG or the monoclonal antibody BB2 were not responding. Cells positive or negative for IgM, IgD, Burkitt's lymphoma antigen (BLA), BB1, and HB2 were all transformed by EBV.

Surface marker characterization of EBV target cells in normal blood and tonsil B lymphocyte populations

Human FACS-sorted B lymphocyte subpopulations were investigated for their susceptibility to immortalization by Epstein Barr virus (EBV). Only B cells reacting with the monoclonal antibody B2 were immortalized, whereas cells reacting with anti-human IgG or the monoclonal antibody BB2 were not responding. Cells positive or negative for IgM, IgD, Burkitt's lymphoma antigen (BLA), BB1, and HB2 were all transformed by EBV.

Amplification of the c-myc oncogene in human plasma-cell leukemia

We have examined primary leukemia cells from multiple myeloma and plasma-cell leukemia patients for rearrangement, amplification and expression of c-myc oncogene. No rearrangement or detectable amplification of the c-myc could be found in 21 cases of multiple myeloma. In contrast, 2/3 cases of plasma-cell leukemia showed amplification of the oncogene with concomitant higher level of expression.

[Physiologic effect of short AV intervals on LV filling time in VDD pacemakers--mitral valve closure in relation to atrial and ventricular contraction]

The effect of mitral valve closure on LV filling time and the onset of LV systole were assessed in 21 normals, 11 patients with left bundle branch block and in 19 patients with VDD pacemakers, which were programmed for the AV intervals 50, 150 and 250 ms, by means of echo-apexcardiography. Mitral valve closure was significantly delayed with increasing delay of intraventricular conduction: 52 +/- 11 ms in normals, 65 +/- 20 ms in LBBB patients and 127 +/- 14 ms in VDD patients. There was a similar distribution of the apexcardiographic upstroke and aortic valve opening in the 3 groups. With increasing AV intervals mitral valve closure was earlier: 127 +/- 14 ms at AV = 50 ms, 83 +/- 38 ms at AV = 150 ms and 20 +/- 75 ms at AV = 250 ms whereas the onset of LV systole and mitral valve opening remained unaltered. Thus filling time expressed in percent of cycle length was reduced from 50 +/- 6% at AV = 50 ms to 45 +/- 9% and to 38 +/- 10% at AV = 250 ms (p less than 0.001). The late onset of LV systole in VDD pacemaker patients therefore reduces LV filling time unless this is compensated by programming a short AV interval in order to maintain the physiological interval between atrial and ventricular contraction.

A new approach to gene mapping by in situ hybridization on isolated chromosomes

A new technique was developed for in situ hybridization on isolated murine chromosomes. The safety and relative rapidity of the method is due to the ready availability of large numbers of isolated "target" chromosomes with well preserved morphology. Its applicability was demonstrated by mapping c-myc to band 15D of Robertsonian (6;15) fusion chromosomes. This localization coincides with the cytogenetic mapping of the translocation breakpoints in mouse plasmacytomas that carry the typical rcpt (12;15) translocation.

[Autoimmune hemolysis caused by anti-Pr]

Following an infection with mycoplasma pneumoniae, an anti-Pr-antibody developed in a hitherto healthy man, aged 41. Within a period of 5 days the antibody caused a severe autoimmune hemolytic reaction. The patient died on the fifth day after admission due to hemolysis and uremia. The autoantibody showed a reactivity with a broad thermal range from 4 degrees C to 37 degrees C. As an initial warning sign, the patient presented an expressed livedo reticularis. Massive wholeblood exchanges could not stop the fatal process.

Antibodies against synthetic peptides react with the second Epstein-Barr virus-associated nuclear antigen

Five peptides were synthesized on the basis of amino acid sequences predicted from the transformation-associated BamHI WYH region of the genome of the Epstein-Barr virus (EBV). Antisera to two peptides deduced from a 1.6-kb open reading frame in the BamHI H fragment identified an 87 000-dalton nuclear polypeptide that was present in EBV-carrying cell lines that expressed the second EBV-determined nuclear antigen (EBNA-2). This polypeptide was not detected in cell lines that carried EBV variants with a deleted BamHI WYH region or in EBV-negative cell lines. Three peptides deduced from the 1.6-kb open reading frame reacted with human EBNA-positive sera, but not with EBNA-negative sera. Following affinity purification with the peptides, two of the corresponding human antibodies also reacted with the 87 000-dalton polypeptide.

Nuclear medical determination of left ventricular diastolic function in coronary heart disease

In 64 patients with coronary heart disease, the left ventricular diastolic function was determined by means of a new nuclear medical method (nuclear stethoscope). The investigations revealed an abnormal diastolic filling in 85.9% of the cases on the basis of the parameters peak filling rate and time to peak filling rate as manifestation of a disturbed ventricular function.

Evolution of tumours and the impact of molecular oncology

It is generally accepted that tumours arise through the accumulation of several changes affecting the control of cell growth. Recent advances in molecular biology have made it possible to define some of these changes in molecular terms and to trace the steps by which certain tumours evolve.

[Studies on the differentiation of chondrocytes in connection with poly ADP ribose synthesis]

Cell differentiation and the behaviour of poly-(ADP-ribose)-synthesis after treatment with methoxybenzamide and procaine was examined in chondrocytes of cell cultures from albino rats. In this study an increase in cell differentiation was connected with a higher level of poly(ADP-ribose)-synthesis. On the basis of an increase in poly(ADP-ribose)-synthesis in chondrocytes an improved scheme of treatment of some rheumatic diseases could be developed.

Characterization of a second Epstein-Barr virus-determined nuclear antigen associated with the BamHI WYH region of EBV DNA

The Epstein-Barr virus-determined nuclear antigen (EBNA) is the only known virally-determined component that is regularly associated with EBV-transformed cells. A main component of EBNA, herein designated EBNA-1, has been conclusively localized to the BamHI K fragment of the viral genome. EBNA-1 is present in all EBV-carrying cell lines so far studied. Our current study deals with a second component. We have found that the EBNA reaction detected by anti-complement immunofluorescence (ACIF) in Burkitt lymphoma lines Daudi, Jijoye, and P3HR-1 could be completely removed by preabsorption of sera with any one of these 3 lines, when tested against any other of them. The same absorbed sera still gave a brilliant nuclear staining against other EBV-carrying lines, e.g. Raji or B95-8. The 3 lines in the first category carry EBV genomes that have deletions in the BamHI WYH region of the EBV genome. This region is intact in the second group of lines. This result is interpreted as showing the existence of 2 different ACIF-stainable EBV-determined nuclear antigens, one of which is associated with the BamHI WYH region. We designate this antigen as EBNA-2. We found that the two different EBNAs are different with regard to their association with metaphase chromosomes. In lines positive for both EBNA subtypes, metaphase chromosomes gave brilliant EBNA-1 staining, but could not be stained for EBNA-2, indicating differences in chromatin association of the two EBNAs. An 86 kd polypeptide was identified by immunoblotting of DNA-binding proteins from EBV-transformed lymphoid cell lines. EBV-specificity of the polypeptide was demonstrated by the presence of antibodies against this polypeptide in antisera from a population of EBV-seropositive donors, but not from seronegative donors, by the presence of the polypeptide itself in EBV-carrying but not in EBV-negative cell lines and by the appearance of antibodies against this polypeptide during the course of infectious mononucleosis (IM). The polypeptide was absent from the EBV-carrying P3HR-1, Daudi and Jijoye cell lines, which suggested that it may be encoded by the BamHI WYH region that is deleted from the viral substrains carried by these lines.

Effect of cyclosporin-A (CsA) on the ability of T lymphocyte subsets to inhibit the proliferation of autologous EBV-transformed B cells

We have analyzed the effect of Cyclosporin-A (CsA) on the in vitro suppression of Epstein-Barr virus (EBV)-induced B-cell proliferations separated on the basis of cell density. CsA abolished the growth-inhibitory capacity of high-density T cells but influenced only marginally the activity of low-density lymphocytes; this suggested that different mechanisms mediate suppression in the two subsets. Stimulation with irradiated EBV-transformed cells had a different impact on the activity of low- and high-density lymphocytes. Proliferative and cytotoxic responses were inversely correlated, i.e. high-density cells proliferated but exerted low cytotoxicity, while the lytic activity of the low-density subset was stronger in the absence of significant cell proliferation. Proliferation and generation of cytotoxicity were abrogated by CsA in both subsets. The activities could be restored by addition of exogenous IL-2, suggesting that the drug may interfere with the cascade of lymphokine--cell interactions which leads to activation of immune responses. From the analysis of athe CsA effects on the two subsets it seems that the high-density one contains specific memory T cells which are activated and proliferate upon encounter with EBV-infected cells. On the other hand, low-density lymphocytes are induced to release soluble factors with antiproliferative activity. The secretory function was resistant to the suppressive effect of CsA.

Thyroid function in epileptic mothers and their infants at birth

It has been suggested that patients receiving anticonvulsant therapy have depressed thyroid function. Thyroid function was studied in 16 pregnant epileptic women who were receiving various anticonvulsants; 20 nonepileptic pregnant women served as controls. Maternal and umbilical cord blood was collected at delivery and serum thyrotropin, total thyroxine, triiodothyronine, triiodothyronine resin uptake, and free thyroxine levels were measured. The free thyroxine index was calculated from the thyroxine and triiodothyronine resin uptake data. There were no significant differences in any of the maternal parameters. In cord serum, the thyroxine level was significantly lower (p less than 0.001) in the infants of the epileptic mothers. The triiodothyronine resin uptake was slightly increased in the epileptic group (p less than 0.05) so that the free thyroxine index largely compensated for this. The thyrotropin, free thyroxine, and triiodothyronine levels did not differ between the two groups. Thus the low thyroxine values in cord blood of infants of epileptic mothers receiving anticonvulsants probably reflect an alteration in protein binding rather than a true alteration in thyroid function.