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Nuclear DNA-binding proteins were extracted from lymphoblastoid cell lines transformed with Epstein-Barr virus (EBV) or with the related lymphotropic herpesviruses of gorilla (Herpesvirus gorilla), chimpanzee (H. pan), baboon (H. papio) or orang-utan (H. pongo). They were immunoblotted with the sera of all four simian species in comparison with EBV antibody-positive human sera. Eight nuclear proteins were identified, and were designated GONA-1 and GONA-2 for H. gorilla-determined nuclear antigens, PANA-1A, PANA-1B and PANA-2 for H. pan, PONA-2 for H. pongo and HUPNA-1 and HUPNA-2 for H. papio-determined nuclear antigens. One of two tested HUPNA-2-positive baboon sera and one PONA-2-positive orang-utan serum also reacted with EBNA-2 in EBV-transformed cells. A human serum that contained antibodies to all five EBNA proteins cross-reacted only with PANA-2 and PONA-2. Monospecific anti-peptide antibodies against EBNA-2, type A, also reacted with PONA-2, but not with the other simian nuclear antigens. The data provide evidence that EBV-like simian lymphotropic herpesviruses induce EBNA-like nuclear antigens and that EBNA-2 and some simian EBNA-related proteins contain an epitope that has been conserved during the evolution of the EBV family of viruses.

Cotton-topped (CT) or white-lipped (WL) marmoset lymphocytes were transformed in vitro with herpesvirus papio (HVP) into permanently growing lymphoblastoid cell lines (LCL). Five of 9 HVP-transformed CT cell lines contained cells with antigens reacting with antibodies to Epstein-Barr virus (EBV) capsid antigen (VCA) and/or to EBV-induced early antigens (EA). None of 12 WL LCL revealed such antigen-producing cells. Cells from both groups of cultures failed to react with antibodies to the EBV-specified nuclear antigen (EBNA). Exposure of baboon circulating lymphocytes to X-irradiated HVP or EBV-carring cells, or to suspensions of EBV resulted in establishment of LCL which all contained VCA and/or EA-positive, but no EBNA-positive cells. Nuclear antigens were undetectable also with anti-VCA-positive sera from baboons, chimpanzees, or other non-human primates. DNA-complementary RNA (cRNA) filter hybridization with EBV cRNA showed that with one exception transformed CT or WL marmoset cells contained at least 1-2 virus genome equivalents per cell, while at least 12-25 virus genome equivalents per cell were detected in transformed baboon cells. These data need confirmation by DNA-DNA reassociation kinetics.

Blastoid cell cultures derived from leukocytes of patients in the acute stage of infectious mononucleosis (IM) and harboring Epstein-Barr (EB) virus in at least 1% of the cells were found to possess antigens in their membranes which presently are indistinguishable from those detected in Burkitt's lymphoma (BL) cells by the techniques employed. It was noted that, in the course of IM, antibodies are formed which react in indirect immunofluorescence tests with membrane antigens of live cells from Burkitt tumor lines as well as from IM leukocyte cultures, including an autochthonous line in the case of one patient. Sets of sera from IM patients were tested which included a serum collected weeks to years before onset of illness. In the majority of these the pre-IM serum failed to react in membrane immunofluorescence (MIF) tests with any of several Burkitt tumor cell lines employed, but in some cases the presera reacted with cells of some but not others of the lines. Possible explanations for these discrepant results have been discussed. The antibodies involved in the MIF test are evidently distinct from those responsible for the EBV and heterophile reactions. Maximal MIF activity is attained long after the other two antibodies have reached maximal titers and antibodies to EBV and membrane antigens seem to persist for years whereas the heterophile reaction turns negative within a few months.

Cultured Burkitt cells were examined by immunofluorescence, autoradiography, and electron microscopy in an effort to identify the stainable cells with those harboring herpes-type virus particles. Immediately after a 2-hr pulse of (3)H-thymidine, from 30 to 60% of the cells revealed heavy nuclear labeling. In most cases the grains were evenly dispersed, but in about 3 to 5% the grains showed a focal distribution and occasionally they extended into the cytoplasm. Such nuclear foci were rarely seen at 8 hr after the pulse. When the analysis was restricted to preselected immunofluorescent cells, up to 80% showed label at 8 hr and cytoplasmic grains were prominent. To reduce cellular deoxyribonucleic acid (DNA) synthesis, cells were X-irradiated with 3,000 to 6,000 R, and the isotope pulse was applied 1, 4, or 7 days later. Whereas the total number of labeled cells decreased in roughly twofold steps at the respective intervals (from 40 to 10%), the incorporation of (3)H-thymidine into fluorescent cells was not affected by X irradiation. In each series, about 70% of the fluorescent cells contained label when they were examined at 24 and 48 hr after the pulse, whereas at 8 and 72 hr fewer were positive. At the earlier intervals, unlabeled fluorescent cells most likely represented cells which had completed viral DNA synthesis prior to the pulse; at the later intervals, unlabeled fluorescent cells were probably cells which commenced viral replication after the pulse. These data support the conclusion that the immunofluorescent cells are the ones which harbor virus, and also confirm the expectation that the virus is a DNA virus from a member of the herpes group. This conclusion was firmly established by sectioning and electron microscopic examination of individual fluorescent cells, all of which contained numerous virus particles, whereas the nonstained cells prepared in a similar manner were free of them.

Efforts were made to elucidate the nature of the resistance to vesicular stomatitis virus (VSV) observed in MCN cultures persistently infected with Newcastle disease, mumps, or 6-6 viruses (MCN(NDV), MCN(Mps) and MCN(6-6), respectively). Cells derived from persistently infected cultures adsorbed VSV to the same extent as their uninfected counterparts. Only a fraction of the adsorbed virus could be recovered from the cells indicating that it enters into an eclipse in all of the cell types. While propagation of VSV in MCN cells is largely inhibited at low pH levels, the resistance of persistently infected cultures could not be ascribed to their increased lactic acid formation. Resistance was not absolute in that a few cells in persistently infected cultures apparently supported VSV reproduction. Furthermore resistance of the cultures was found to be transitory in that the VSV infection gradually gained the upper hand after 2 to 4 weeks of incubation. Addition of ultraviolet-inactivated NDV to MCN cultures induced resistance to VSV as long as the equivalent of at least one ID(50) (for chick embryos) of inactivated virus was provided per cell. Establishment of resistance required some time and its duration depended upon whether or not the free inactivated NDV was removed or neutralized after given adsorption periods. The transitory nature of resistance in persistently infected cultures, or in MCN cells following adsorption of inactivated NDV, is most likely explained by the fact that the cells continue to divide and that the daughter cells are, at least in part, susceptible to VSV. The results are compatible with the conclusion that the resistance observed represents another example of interference between 2 viruses.

Cultured cells derived from male patients with Burkitt's lymphoma and harboring herpes-type virus particles were lethally irradiated. These irradiated cells induced normal peripheral leukocytes of female infants to grow within 2 to 4 weeks after mixed cultivation. Cells of a line free of this agent failed to stimulate growth. If either type of cell was cultured separately, it did not survive under the experimental conditions. Herpes-type viral antigen and C-group chromosomal marker previously described in cultured Burkitt cells were found in all of the female cell cultures that were obtained.

After incubation at 37 C for 2 or more days, Basal Medium Eagle (BME) supplemented with 25% fetal calf serum (FCS) was not able to support adequate growth of EB3 and other lines of Burkitt tumor cells. The medium did, however, increase, by a factor of about 10, the number of cells synthesizing herpes-type virus with which the cultures were persistently infected. Not every lot of FCS produced these effects, nor were these effects seen when BME and FCS were incubated separately for 7 days before the medium was completed. At 37 C, appropriate lots of FCS interacted with several of the amino acids present in BME; this interaction resulted in an inhibition of cellular growth, whereas interaction with arginine yielded the virus-enhancing effect. Arginine-free BME, supplemented with 25% FCS and used without prior incubation, prevented cellular replication and promoted viral infection to a similar extent as did preincubated complete medium. Replenishment of arginine reduced, but did not regularly abolish, the virus-enhancing activity of preincubated media. RPMI-1629 medium was less affected by preincubation with FCS because it contained twice the amount of arginine that BME contained. The FCS factors which act upon arginine and other amino acids are not dialyzable and are partially resistant to heating at 56 or 60 C for 30 to 60 min. Calf and horse sera appear to be devoid of these activities. The nature of these interactions, as well as the mechanism by which arginine deficiency enhanced the viral infection, remains to be ascertained.

A comparison was made of the immunofluorescence tests for detection of cell membrane and Epstein-Barr virus antigens in cells from Burkitt tumor biopsies or continuous cultures derived therefrom. On the whole, cell membrane fluorescence in established lines appeared to depend not only upon the presence of EBV but to a considerable degree also upon the extent of the persistent viral infection. There was no constant relationship, however, between the results of the two tests and exceptions to the rule were noted. These observations indicate that different antigens are involved in the two tests. Biopsy cells in general and young cultures may reveal strong MIF activity but few, if any, EBV-positive cells. The reverse, the presence of relatively large numbers of EBV antigen-containing cells in the absence of significant MIF reactions, was also noted on occasion in a few established cultures. The possible interpretations of these findings have been discussed.

CULTURES WERE INITIATED WITH PERIPHERAL LEUKOCYTES FROM INDIVIDUALS: (i) in the acute stage of infectious mononucleosis (IM); (ii) with past histories of IM; and (iii) without histories of IM and without antibodies to EB virus (EBV). In confirmation of other reports, the first group of cultures developed readily and rapidly into lines of blastoid cells. Cellular replication commenced in 24 of 25 attempts within 17 to 28 days, regardless of the technique employed; i.e., initial seeding of the leukocytes with or without addition of phytohemagglutinin onto monolayers of human diploid cells (WI-38) or direct establishment of suspension cultures. EBV was detected in all cultures by immunofluorescence and also by electron microscopy when tested. Furthermore, the nine cultures which were examined cytogenetically revealed the C-group (#10) chromosomal marker previously found in cultured Burkitt tumor cells. These findings supported the earlier conclusion that EBV is related to, if not identical with, the causative agent of IM. Cultures of the second group commenced growth only within 30 to 60 days in five of seven attempts, depending apparently upon the early presence of WI-38 cells. These cultures also revealed the presence of EBV and, in the three examined, the C-group chromosomal marker. Leukocytes of the third group, seeded onto WI-38 monolayers, failed to become established in four attempts. The possible implications of these findings are discussed.

Inoculation of 64-10 or Raji cultures with Epstein-Barr virus derived from the HRI-K clone of the P3J Burkitt's lymphoma line caused abortive infections in most of the lymphoblastoid cells with synthesis of "early antigens" but few, if any, capsids. Antibodies to early antigens were detected by indirect immunofluorescence in serums of many patients with infectious mononucleosis, Burkitt's lymphoma, or nasopharyngeal carcinoma. These antibodies were rarely present in other serums even though some of them showed high titers of antibodies to Epstein-Barr virus when assayed on EB3 Burkitt tumor cells; they also prevented synthesis of early antigens, provided the serums were mixed with the virus prior to inoculation. Antibodies to early antigens possibly reflect current or recent disease processes that are associated with the virus.