Leukocyte migration inhibition demonstrates a human T-cell response to a membrane protein expressed in latent Epstein-Barr virus infection

Sequence analysis of Raji Epstein-Barr virus DNA

The DNA sequence of the EcoRI Dhet and part of the BamHI E fragments of Raji EBV has been determined. Precise locations of two deletions in Raji DNA have been identified and their consequences for gene structure evaluated. The deletion in Raji of reading frames BALF1, BARF1, and BZLF2 and truncation of BALF2 and BERF5 probably account for the replication defect in this strain. The degree of sequence variation between B95-8 and Raji has been examined and shows considerable variation between genes. The latent membrane protein gene is exceptionally polymorphic and the initiator methionine for the late productive cycle protein overlapping the latent membrane protein is absent in Raji.

Cellular and humoral immune responses to synthetic peptides deduced from the amino-acid sequences of Epstein-Barr virus-encoded proteins in EBV-transformed cells

Ten synthetic peptides containing 18-22 residues deduced from the amino-acid sequences of the EBV-encoded latent-infection-associated membrane protein (LMP) and the 2 principal nuclear antigens, EBNA-1 and EBNA-2, were tested for their ability to induce lymphokine release from sensitized T-cells of EBV-seropositive donors, as measured by the leukocyte migration inhibition assay (LMI). Only one of the 10 free peptides induced EBV-specific LMI. After Sepharose-coupling, 4 additional peptides were regularly active. In parallel, the sera of the same and other donors were screened for synthetic peptide-binding antibodies, as measured by an ELISA assay. Antibodies to 9 of the 10 peptides were detected in 25-80% of EBV-antibody-positive, but not in EBV-antibody-negative sera. A comparison of the two responses indicates that the humoral immune system tends to react with more epitopes on a given protein than the cellular immune system. Furthermore, the antibody reactivity pattern to different epitopes is more variable from individual to individual than the T-cell response. Also, the epitopes detected by antibodies and sensitized T-cells are often not identical.

Down-regulation of the EBV-encoded membrane protein (LMP) in Burkitt lymphomas

A radioimmunoassay (RIA) has been developed and used to determine the expression of LMP-a membrane protein encoded by the LT3 region of the Epstein-Barr virus (EBV) genome-in cell lines of various origins. The RIA was highly sensitive, specific and reproducible. All EBV-negative cell lines were LMP-negative and 18 of 21 EBV-carrying cells were LMP-positive. LMP concentrations varied widely, ranging approximately from less than 4 ng up to 650 ng/mg protein. In several instances comparisons were made between lymphoblastoid (LCLs) and Burkitt lymphoma (BL) cell lines (EBV-positive or EBV-converted sublines of originally EBV-negative BL) originating from the same patient. In all such cases LMP and LMP-specific mRNA levels were higher in the LCLs. Most of the LMP was found in the cytosol fraction, yet this fraction was negative in immunoblotting tests. However, antiserum preincubated with the cytosol lost its ability to react in immunoblotting with membrane LMP, indicating that the 2 LMP forms (membrane and cytosol) are completely cross-reactive.

Stable transfection of a human lymphoma line by sub-genomic fragments of Epstein-Barr virus DNA to measure humoral and cellular immunity to the corresponding proteins

An Epstein-Barr virus (EBV)-negative human lymphoid B-cell line, DG75, was stably transfected with recombinant selection vectors that carry a subfragment of the BamHI WYH region (nucleotides 44664 to 50628), the BamHI K fragment, or a subfragment of the EcoRI D region (nucleotides 166614 to 170149) of B95-8 EBV DNA. These fragments contain the coding exons for the EBV-determined nuclear antigens EBNA2 and EBNA1, and the membrane antigen LMP, respectively. Antigen expression of the cells was detected by immunofluorescence. EBNA2 was expressed in 80-100% of the transfected cells, in contrast to EBNA1 which was expressed in only 25%, and LMP in only about 5% of the cells. Humoral antibody responses were measured by immunofluorescence and compared to cellular immunity as determined by the leukocyte migration inhibition (LMI) technique. Extracts from transfected cell lines expressing EBNA1, EBNA2 or LMP elicited an LMI response with cells from healthy EBV-seropositive individuals whereas the extract from the parental DG75 cell line did not. The results demonstrate the value of stably transfected cell lines expressing a defined EBV antigen for the monospecific analysis of host responses to the EBV-encoded antigen complex in growth-transformed cells.

Enhancement of Epstein-Barr virus membrane protein (LMP) expression by serum, TPA, or n-butyrate in latently infected Raji cells

The BamHI Nhet region of the EBV DNA is known to code for two proteins. One is a membrane protein (LMP) with an apparent molecular weight of 60,000 on SDS-PAGE which is expressed in latently EBV infected cells. The second protein, so far unidentified, is presumably a late protein with a calculated molecular weight of 28,000 Da. Antisera against both proteins were generated by immunizing rabbits with either a fusion protein containing 155 amino acids of the C-terminus of LMP and a 37,000 mol wt piece of the bacterial anthranilate synthase or with a C-terminal synthetic peptide of 7 amino acids. These sera reacted with a protein varying in size between 60,000 and 65,000 mol wt on SDS-PAGE, found in all cell lines harboring EBV. In addition, these sera identified a second protein with an apparent molecular weight of 49,000 on SDS-PAGE in B95-8, P3HR-1, and M-ABA cells, which is presumably identical with the 28,000-Da protein mentioned above. Furthermore, with these sera a positive cytoplasmic immunofluorescence in 1 to 10% of the cells was obtained, depending on the cell line examined. Analyzing the nonproducer Raji cell line, the number of immunofluorescence-positive cells and the amount of the 60,000 protein, as judged by immunoblotting, was rapidly increased by addition of fresh medium with 10% fetal calf serum as well as by the tumor promoter TPA or to an even higher extend by n-butyrate. The kinetics of induction reached a maximum 24 hr after addition of medium plus 10% fresh serum or TPA or n-butyrate and decreased after 24 to 48 hr. Since the induction of the EBV early antigen (EA) associated proteins by TPA or n-butyrate exhibits a diverse kinetic with a maximum at 72 hr, the regulation of the 60,000 protein synthesis appears to be different from known EA-associated proteins.

Epstein-Barr virus (EBV) antigen-specific leukocyte migration inhibition (LMI) in infectious mononucleosis (IM). I. Kinetics and response to a membrane protein on EBV-transformed cells

Cell-mediated immune response of mononucleosis (IM) patients to Epstein-Barr virus (EBV)-determined antigens was measured by the leukocyte migration inhibition (LMI) assay. Patients in the acute phase of the disease failed to respond to partially purified nuclear antigen, EBNA, or to cell extracts that contained EBNA as the predominant EBV antigen. They showed a strong specific response to cell extracts enriched in early antigen (EA) and virus capsid antigen (VCA). The LMI response to EBNA appeared in convalescence in parallel with EBNA-specific antibodies, slightly later in children than in adults. Membrane fractions of EBV-carrying, virus nonproducer Raji cells induced an EBV-specific LMI at approximately the same time. A bacterial fusion protein containing the hydrophilic part of the virus-coded membrane antigen of latently EBV-infected cells also induced an EBV-specific response that parallelled the LMI reaction elicited by the Raji membrane fraction. This is in line with our previous finding (D. Sulitzeanu et al., J. Virol. 58, 230, 1986) that this fusion protein shares an epitope with Raji cell membranes.

Nucleotide sequences of mRNAs encoding Epstein-Barr virus nuclear proteins: a probable transcriptional initiation site

Three cDNA clones of the second Epstein-Barr virus nuclear antigen (EBNA2) mRNA and two of the EBNA1 mRNA were analyzed. Two EBNA2 clones begin 42 bases 3' to a promoter in the Epstein-Barr virus long internal repeat, which is likely to be the EBNA2 promoter. Surprisingly, the first splice creates an AUG at the beginning of the first of two nonoverlapping open reading frames. The second open reading frame encodes EBNA2. Two incomplete EBNA1 mRNA cDNA clones begin with parts of two of the EBNA2 exons and contain two other exons that map 19 and 59 kilobases 3' to the EBNA2 coding domain. The 3' exon of this mRNA encodes EBNA1. A model for regulation of transcription of these RNAs is presented.