Epstein-Barr virus susceptibility of normal human B lymphocyte populations.

Human blood and tonsil B lymphocytes were fractionated on density gradients and tested for virus binding and penetration into the cells. Epstein-Barr Virus (EBV) transformation was detected by immunofluorescence staining for EBV-determined nuclear antigen (EBNA). EBV bound to and penetrated all B cell populations, but only the high density populations were transformed. Activated B lymphocytes were found in the low density fractions and these cells were resistant to EBV infection. Infected and noninfected B lymphocytes were density-analyzed during in vitro culture. A spontaneous, not virus-induced, density decrease was found to precede the production of EBNA. Cells remaining at high density never expressed EBNA. The results suggest that EBV can transform only small resting B lymphocytes and that a virus-independent activation of the infected cells induces the EBNA production and transformation.

Surface marker characterization of EBV-carrying cells in blood of healthy seropositive individuals.

We have determined the phenotype of EBV-carrying cells in human blood by establishing spontaneous LCLs from populations selected according to three B cell markers, B1, B2, and 35.1C5. LCLs grew from the B1-positive, B2-positive, B2-negative and 35.1C5-positive population. Thus, EBV-carrying cells in blood of seropositive individuals are restricted to the B cell lineage. These B cells may or may not express the B2 epitope, and they may be derived from the lymph node mantle zone or the splenic marginal zone. These in vivo EBV-carrying cells could enter the viral productive cycle and transform coresident B cells during the initial 3 days in vitro. The characteristic of the LCLs with regard to these 3 B cell markers did not correspond to the original B cell population from which they were derived.

Distinction between Burkitt lymphoma subgroups by monoclonal antibodies: relationships between antigen expression and type of chromosomal translocation.

Twenty-six lines derived from 22 Burkitt lymphoma patients were examined for cytoplasmic vs. surface immunoglobulin and the expression of the monoclonal-antibody-detected BLA, CALLA and LB-I antigens. Six of the lines carried the variant translocations 8;2 or 8;22 (three each), 17 lines had the typical 8;14 translocation, I was translocation-negative (BJAB) and 2 were not examined cytogenetically. Depending on their immunoglobulin and surface marker expression, the BL lines could be subdivided into several subgroups. There was a strong inverse correlation between the expression of the CALLA and the LB-I marker. All BLA-lines were CALLA-, whereas the CALLA+ lines could be either BLA- or BLA+. All six variant translocations belonged to the CALLA-BLA-LBI+ category. Only one set of three lines, derived from the patient with the 8;14 translocation, belonged to the same subgroup. This suggests that the typical vs. the variant translocation freezes the BL cell at a different stage of differentiation. The variant translocation-carrying subtypes represent probably a somewhat more advanced stage of differentiation.

gp140, the C3d receptor of human B lymphocytes, is also the Epstein-Barr virus receptor.

The relationship between gp140, the membrane C3d receptor (CR2) of human B lymphocytes, and the Epstein-Barr virus receptor (EBVR) was analyzed by using the polyclonal anti-gp140, previously prepared by immunizing rabbits with highly purified gp140 (isolated by some of us) from CR2/EBVR-positive Raji cells. Polyclonal anti-gp72, a C3-binding membrane component, not related to the EBVR but also expressed on the Raji cell surface, was used as a control. Binding of rabbit IgG and EBV on cells was assessed by using immunofluorescence techniques with analysis by flow cytofluorometry. A semiquantitative bioassay was also used to measure the EBV binding. Polyclonal monospecific anti-gp140 IgG inhibits directly the binding of EBV to Raji cells at the same concentration that inhibits the binding of EC3d on cells, whereas a 35 times higher concentration of anti-gp72 IgG or preimmune serum IgG does not. Anti-gp140 IgG treatment also inhibits the induction of EBV-determined nuclear antigen in normal tonsil B lymphocytes or in EBV-negative Ramos cells, whereas high concentrations of anti-gp72 IgG or preimmune serum IgG have no effect. These data strongly suggest that gp140, the CR2 of human B lymphocytes, is also the EBVR.

Subgroup analysis of BL-cell lines with polyclonal BL-specific antibodies.

A Burkitt's lymphoma (BL)-specific antibody (anti-GP70), previously described, was used to analyse 22 different BL-cell lines. The results indicated specificity of antibodies to lines that contain both surface membrane Ig (SmIg) and cytoplasmic Ig (CyIg). BL-cell lines derived from more immature B cells that do not have SmIg but rather have only CyIg were negative. A comparative study with antibody to common ALL antigen (CALLA) and to another BL-specific antigen (BLA) revealed coexpression of GP70 with those two antigens, but no identity between them.

Immunophenotypic characterization of follicle-center-cell-derived non-Hodgkin's lymphomas.

The distribution of the BLA, CALLA (CD 10), AC-2 (CD 39), MHM-6 (CD 23), LB-I, and 351C5 (CD 45R) antigens in 40 non-Hodgkin's lymphomas was demonstrated by immunohistochemical staining of frozen tissue sections. Nine out of 10 centroblastic and centrocytic follicular and diffuse type of lymphomas (CB/CC F/D) and all 10 cases of CB/CC follicular lymphomas were BLA+ and CALLA+. A few cases also showed weak expression of activation antigens (AC-2, MHM-6 and LB-I) and 351C5. In contrast, 3 CC and 3 lymphoblastic (non-Burkitt) lymphomas showed a heterogeneous pattern of distribution with dominating activation antigen expression. A single case of lymphoblastic lymphoma of Burkitt-like type expressed BLA and CALLA but not activation antigens. In reactive follicular center and FCC lymphomas different cell populations appeared to express BLA and activation antigens, respectively. Assessment of staining intensity and proportion of the stained cells indicated that almost all BLA+ cells are CALLA+. CALLA+ BLA- cells were regularly present, in addition. The co-expression of BLA and CALLA in the same cell was confirmed by double immuno-enzymatic staining. By the same technique, BLA+ and CALLA+ cells were shown to be activation-antigen negative.

Correlation between the growth-inhibitory effect of TGF-beta 1 and phenotypic characteristics in a panel of B-cell lines.

Human B-cell lines established from Burkitt lymphoma (BL) and normal B cells immortalized in vitro by EBV (LCLs) differ in phenotype. While the BL correspond to resting B cells, the LCLs resemble activated B cells. When BLs which have the EBV genome are carried in vitro, they acquire some of the features of LCLs, such as expression of B-cell activation markers and the tendency to form aggregates. Comparison of several B-cell lines for sensitivity to TGF-beta showed that the growth of BLs (with few exceptions), but not of the LCLs, was inhibited. The results suggested that the sensitivity to TGF-beta correlates with the cellular phenotype. In the present work, this assumption is even more critically substantiated by studying 2 sublines of an EBV-genome carrying BL line, Mutu, which were selected for single cells and aggregates. The former (with resting phenotype) was inhibited, while the subline of aggregated cells, which also expressed B-cell activation markers, was not inhibited. Somatic-cell hybrids between BLs, LCLs and non-B cells provided lines with phenotypic differences. Results with a panel of such hybrid lines also showed that those which express the activated B-cell phenotype are not inhibited by TGF-beta. Differences in the levels of expression of activation markers did not influence the response to TGF-beta.

Scavenger receptors mediate adhesion of activated B lymphocytes.

The scavenger receptor (SR-A) is considered to play a role in host defense by scavenging endotoxins, oxidized proteins, and denatured or otherwise modified self components, which are routed toward degradation in macrophages. Recent data suggest that SR-A also functions as an adhesion molecule. Our previous finding of SR-A expression by high endothelial cells of venules and on follicular dendritic cells in peripheral lymph nodes prompted us to investigate whether SR-A can act as an addressin for lymphocytes. We describe here that activated B cells adhere to CHO cells transfected with either the type I or type II isoform of SR-A. In contrast, resting B cells isolated from peripheral blood did not adhere to SR-A transfected CHO cells. Other types of leukocytes did not bind to SR-A. The adhesive properties of B lymphocytes in different stages of activation were further explored using lymphoma cell lines of the B cell lineage. The in vitro EBV-transformed B cell line IARC171 showed enhanced adhesiveness to SR-A, whereas the Burkitt lymphoma cell lines, BL41, Rael, and Bl16 did not. The SR-A-dependent adhesion of B-lymphoblasts occurred both at 37 and 4 degrees C, suggesting that it was not dependent on cell metabolism. The known polyanionic ligands for SR-A, fucoidan, and acetylated low density lipoprotein, which bind to a positively charged portion of the collagen-like domain of SR-A, did not inhibit adhesion. This finding suggests that SR-A mediates adhesion of activated B lymphocytes through a binding site that differs from the one that binds polyanionic ligands. Together, our data suggest that SR-A plays a role in the recruitment of activated B cells into lymph nodes and inflammatory lesions by acting as an adhesion molecule for such cells.

Induction of an activated b lymphocyte-associated surface moiety defined by the B2 monoclonal antibody by ebv conversion of an EBV-negative lymphoma line (Ramos): differential effect of transforming (B95-8) and nontransforming (P3HR-1) EBV substrains.

The expression of the B2 antigen, defined by a monoclonal antibody, was studied on Burkitt lymphoma lines, lymphoblastoid cell lines, leukemia and myeloma lines, hybrids between different hemapoetic cell lines, and EBV-converted sublines of originally EBV-negative, B2-negative B lymphoma lines. In confirmation of earlier results, the expression of B2 was found to be restricted to a relatively narrow portion of the B cell maturation pathway. Non-B cell-derived lines were uniformly negative. Hybrids derived from the fusion of highly B2-positive and B2-negative or low B2 expressing lines of B cell origin were B2-positive. In contrast, fusion of B2-positive Burkitt lymphoma lines with the primitive human erythroleukemia line K562 resulted in the complete extinction of B2 expression. These findings are in line with the expected behavior of a B cell differentiation marker. EBV conversion of the EBV-negative, B2-negative Ramos lymphoma line by the transforming B95-8 substrain of the virus regularly induced the expression of B2, whereas conversion with the nontransforming P3HR-1 substrain had no such effect, in spite of the continued presence of EBV-DNA and EBNA in both types of EBV-converted sublines. The possibility that B2 induction may reflect the action of the transforming gene(s), present in B95-8 but deleted from the P3HR-1 virus, and the implications of this possibility for the functional mapping of the EBV genome are discussed.

Expression of B-cell-specific markers in different Burkitt lymphoma subgroups.

Forty-three Burkitt lymphoma (BL) lines were examined for the expression of 5 monoclonal antibody (MAb)-identified B-cell-specific markers and immunoglobulin production. All (13) EBV-negative BL lines were CALLA+ LB-1-, whereas 30 EBV-carrying lines showed a more heterogeneous pattern. In the EBV-negative lines, the follicle mantle zone markers BA-1 and 35.1C5 were expressed concordantly, at a different level in each line. This coordination was disrupted in EBV-carrying lines. In the EBV-negative lines, there was also an inverted correlation between the expression of 35.1C5 and the germinal center marker BLA, suggesting that some etiologically important event, perhaps the translocation, had fixed the cells at different stages of their transition from one zone to the other. This inverted relationship was also disrupted in the EBV-carrying lines, suggesting that EBV can interfere with the maturation program of the BL cell. This conclusion was also supported by a comparison between 5 EBV-negative BL lines and their EBV-converted sublines. All converted lines have undergone marker changes, but the degree and nature of these changes was different for each EBV-BL line. Both the coordinated expression of BA-1 and 35.1C5 and the inverted relationship between CALLA and LB-1 were disrupted in several other convertants. We have reexamined our previous finding (Ehlin-Henriksson and Klein, 1984) that the majority of the variant translocation-carrying BL lines were CALLA- LB-1+, in contrast to the majority of the typical translocation carriers that were mostly CALLA+ LB-1-. All II EBV-negative lines were CALLA+ LB-1-, irrespective of the type of translocation. Among the EBV-carrying lines, 4 of 17 typical (8;14) translocation carriers were CALLA- LB-1+, whereas 7 of the 12 variant translocation-carrying lines were CALLA- LB-1+. The remaining two expressed both antigens to some extent. The difference is statistically significant at the 0.03 level.

A p50 surface antigen restricted to human urinary bladder carcinomas and B lymphocytes.

We have previously described the derivation of a monoclonal antibody, S2C6, to a novel 50 Kdalton antigen associated with human urinary bladder carcinoma. No reactions were obtained with carcinomas of unrelated origin or with normal urothelial cells. However, the antibody also reacted with a similar antigen on some cell lines of B lymphocyte origin. Using large panels of target cells we have now shown that this reactivity was entirely restricted to cells of the B lineage within the haematopoietic system. As opposed to its apparent restriction to malignant cells of the urothelium, the S2C6 antigen was expressed by normal B lymphocytes as well as by many malignant B cells (chronic lymphocytic leukaemia, hairy cell leukaemia and immunocytoma). Pre-B cells derived from acute lymphocytic leukaemia and plasma cells from multiple myeloma lacked the antigen. Expression was significantly enhanced on cultured B cells from Burkitt lymphomas and on Epstein-Barr virus-transformed lymphoblastoid cell lines including those of the pre-B phenotype derived from fetal bone marrow. As judged from the molecular size and the distribution pattern displayed by the S2C6 antigen it appears to be distinct from other B cell antigens previously described. A possible relation of the S2C6 antigen to a receptor for B cell growth factors is discussed.

Capacity of B-lymphocytic lines of diverse tumor origin to produce and respond to B-cell growth factors: a progression model for B-cell lymphomagenesis.

Human cell lines established from cases of acute lymphoblastic leukemia, lymphosarcoma, Burkitt's lymphoma and multiple myeloma and representing stages of B-lymphocyte development ranging from pre-B through to plasma cells, were assessed for their ability to produce and respond to B-cell growth factors (BCGF). All B-cell lines studied were found to be constitutive producers of a growth activity which assisted the S-phase entry of normal activated B-cells and provided growth support for lymphoblastoid cells transformed by Epstein-Barr virus. Furthermore, all lines responded by enhanced proliferation to supernatants from a BCGF-producing T-cell hybridoma. Not all lines, however, displayed autostimulation to their own supernatants and no tumor B-cell line appeared totally dependent on soluble factors for its growth. Non-tumorigenic B-cell lines, by contrast, revealed a strict dependency on homologous growth factor for their continued proliferation in suspension culture. The findings support a progression model of lymphomagenesis based upon the utilization, production and, ultimately, emancipation from growth-promoting soluble factors.

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.

Host cell phenotype-dependent methylation patterns of Epstein-Barr virus DNA.

We have shown previously that the EBNA 1 and latent membrane protein encoding regions of the Epstein-Barr virus (EBV) genome are highly methylated at CCGG sequences in the Burkitt's lymphoma (BL)-derived cell line Rael, but are unmethylated in a lymphoblastoid cell line (LCL) harbouring the same virus. To examine whether this is a regular phenomenon, we compared the methylation patterns of selected regions (BamHI C, W, H, M, E, K and N fragments) of EBV DNA in representative EBV-carrying cell types of normal and neoplastic origin. Analysis of HpaII and MspI cleavage patterns showed that all probed regions were highly methylated in all six BL biopsy samples, but hypomethylated in the four LCLs immortalized by the virus. EBV DNA was also highly methylated in the nude mouse-passaged C15 nasopharyngeal carcinoma strain and partially methylated in the C18 strain. Eight BL lines propagated in vitro, ranging from a typical BL group I to a more LCL-like group III phenotype, showed heterogeneous levels of methylation. Rael, the only stable group I cell line, carried highly methylated viral genomes. The other cell lines, which have drifted to an LCL-like blastic phenotype to various degrees, showed more moderate or low viral DNA methylation. Two sublines of the BL cell line Jijoye, which could be classified as groups II and III, respectively, showed a corresponding difference in EBV DNA methylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Search for the critical characteristics of phenotypically different B cell lines, Burkitt lymphoma cells and lymphoblastoid cell lines, which determine differences in their functional interaction with allogeneic lymphocytes.

Burkitt lymphoma (BL) lines can be grouped according to phenotypic characteristics. Group I cells exhibit the phenotype of resting B cells and grow as single cells. Such lines can be Epstein-Barr-virus(EBV)-negative or -positive. Group II and group III cells are always EBV-positive, they express B cell activation markers, grow in aggregates and resemble in varying degrees lymphoblastoid cell lines (LCL). We studied three groups of BL lines for their capacity to interact with allogeneic lymphocytes. The results showed that as long as the lines have the group I phenotype, they do not stimulate allogeneic T lymphocytes irrespective whether they carry the EBV genome. The group II and III cells are stimulatory. Generally there was no correlation between sensitivity ot lymphocyte-mediated lysis and the phenotype of the lines. In one set of lines, the group I cells had higher sensitivity to both natural killer and lymphokine-activated killer effectors compared to the group II or III lines. However, such correlation could not be seen with the other two sets of lines. Among the phenotypic features investigated, expression of the adhesion molecules LFA-1 and LFA-3 correlated with the tendency for cell aggregation.

Burkitt's lymphoma is a malignancy of mature B cells expressing somatically mutated V region genes.

BACKGROUND: The developmental stage from which stems the malignant B cell population in Burkitt's lymphoma (BL) is unclear. An approach to answering this question is provided by the sequence analysis of rear-ranged immunoglobulin (Ig) variable region (V) genes from BL for evidence of somatic mutations, together with a phenotypic characterization. As somatic hypermutation of Ig V region genes occurs in germinal center B cells, somatically mutated Ig genes are found in germinal center B cells and their descendents. MATERIALS AND METHODS: Rearranged V kappa region genes from 10 kappa-expressing sporadic and endemic BL-derived cell lines (9 IgM and 1 IgG positive) and three kappa-expressing endemic BL biopsy specimens were amplified by polymerase chain reaction and sequenced. In addition, VH region gene sequences from these cell lines were determined. RESULTS: All BL cell lines and the three biopsy specimens carried somatically mutated V region genes. The average mutation frequency of rearranged V kappa genes from eight BL cell lines established from sporadic BL was 1.8%. A higher frequency (6%) was found in five endemic cases (three biopsy specimens and two BL cell lines). CONCLUSIONS: The detection of somatic mutations in the rearranged V region genes suggests that both sporadic and endemic BL represent a B-cell malignancy originating from germinal center B cells or their descendants. Interestingly, the mutation frequency detected in sporadic BL is in a range similar to that characteristic for IgM-expressing B cells in the human peripheral blood and for mu chain-expressing germinal center B cells, whereas the mutation frequency found in endemic BL is significantly higher.

Up regulation of the Epstein-Barr virus (EBV)-encoded membrane protein LMP in the Burkitt's lymphoma line Daudi after exposure to n-butyrate and after EBV superinfection.

The Burkitt's lymphoma line Daudi carries a nontransforming Epstein-Barr virus (EBV) strain that has a deletion in the BamHI WYH region of the genome coding for the EBV nuclear antigen 2 (EBNA-2). Daudi cells fail to express the EBV-encoded latent membrane protein (LMP) (D. Ghosh and E. Kieff, J. Virol. 64:1855-1858, 1990). We show that LMP expression can be up regulated by exposure to n-butyrate and by superinfection with the B95-8 (B virus)- and P3HR1 (P virus)-derived EBV strains. Two LMP polypeptides of 60 and 48 kilodaltons (kDa) were detected in immunoblots of Daudi cells that had been exposed to 3 mM n-butyrate for 24 h. The intensity of the 48-kDa LMP increased during 72 h, in parallel with the appearance of early antigen-positive cells. The 60-kDa LMP was expressed at a low level and remained constant. Superinfection of Daudi cells with B and P virus induced the 60-kDa LMP within 3 h. In addition, P virus induced the 48-kDa LMP at a low level. The B virus-encoded EBNA-2 and EBNA-5 were detected 12 h after superinfection. The B virus-encoded 63-kDa LMP was coexpressed with the endogenous LMP after 48 h. Inactivation of the virus by UV illumination abolished the expression of the B virus-encoded antigens but did not affect the induction of the endogenous LMP. The B-cell activation marker CD23 was up regulated by B virus superinfection but not by n-butyrate exposure. CD23 was also expressed at a higher level in a stable B virus-converted subline, E95A-Daudi, that was EBNA-2 positive and coexpressed the Daudi virus- and B virus-encoded LMP. The results suggest that LMP expression is regulated by the interaction of cellular and viral factors. Binding of the virus to its membrane receptor might be involved in the triggering of cellular control mechanisms. Viral gene products are not directly involved in this function but may contribute to create a permissive cellular environment for LMP expression.

Studies on the B lymphoblast antigen No. 1 (BB-1) on a series of Burkitt lymphoma lines differing in the expression of the EBV/C3 receptor complex.

In the Jijoye-P3HR-1 family of Burkitt lymphoma sublines, the expression of the B lymphoblast-1 antigen, BB-1, identified by the monoclonal antibody described by Yokochi and colleagues, was found to be strictly related to the expression of the EBV receptor/C3 receptor (EBVR/C3R) complex. It was absent on the receptor-negative P3HR-1 line, present in the original receptor-positive Jijoye line, and reappeared in nonvirus producer sublines derived from P3HR-1 itself. We suggest the BB-1 antigen is related to the EBVR/C3R complex in the Jijoye family, either at the level of genetic or epigenetic determination or at the level of steric interaction on the cell membrane. In all probability, however, the BB-1 antigen is not identical to the receptor itself. It is also clear that a similar relationship does not necessarily apply to other cell lines. In the course of the studies, it was accidentally discovered that propagation of the P3HR-1 cells on newborn instead of fetal calf serum induces the concomitant expression of EBV receptors, C3 receptors, and the BB-1 antigen. The mechanism of this induction is obscure; it does not appear to be related to any significant change in the frequency of virus-producing cells.

Expression of the BLA antigen, defined by the monoclonal 38.13 antibody, on Burkitt lymphoma lines, lymphoblastoid cell lines, their hybrids and other B-cell lymphomas and leukemias.

The BLA expression of eight Burkitt lymphoma lines was high, whereas it was negative in four, including the two IgG producers tested. Most lymphoblastoid cell lines (LCL) of normal origin had only a low percentage of positive cells, not significantly above background, although a few had up to 30% positives. EBV conversion of the EBV-negative Burkitt lymphoma line Ramos destabilized the high BLA expression, leading to a decrease in the average number of positive cells in the majority of the converted sublines in parallel with considerable fluctuation in antigen expression within each subline. Our group has previously shown that EBV-conversion of Ramos cells can induce certain differentiation steps (Spira et al., 1981 a). EBV-converted sublines of another EBV-negative Burkitt lymphoma, BJAB, showed a much greater stability previously and remained unchanged with regard to BLA expression in our present experiments. Eight T-cell leukemias, three myeloid leukemia lines and two diffuse histiocytic lymphomas were negative for BLA, whereas two myeloma lines were 30-40% positive. A histiocytic tumor had marginal reactions. Hybrids derived from the fusion of high with low BLA-reactive parental lines showed all three possible patterns (high, intermediate and low), provided that B-cell lines were fused with each other. Fusion of two Burkitt lymphoma lines with the K562 erythroleukemia line led to the extinction of BLA expression, as well as to the eclipse of other B-cell markers. B-lymphoma and leukemia (CLL) cells harvested directly from the patient showed a heterogeneous reactivity pattern. Strong to intermediate BLA expression was found among CLL cells and in most histological groups of B-CLL lymphomas except the centroblastic group (3/3 negatives). IgG-expressing follicular lymphomas were less reactive than IgM +/- IgD lymphomas of the same group. Immunocytomas were also low-reactive. BLA can be thus expressed on a variety of B-cell neoplasms; the degree of its expression appears to be related to the stage of differentiation.

Epstein-Barr virus genomes are found predominantly in IgA-positive B cells in the blood of healthy carriers.

B lymphocytes have been identified as the main reservoir of latent Epstein-Barr virus (EBV) in healthy virus carriers. We have established a semi-quantitative PCR method to estimate the EBV genome load in the blood B-cell subpopulation in healthy individuals. EBV DNA was detected in subfractionated IgM-, IgG- and IgA-positive B cells. Between 80% and 90% of the viral DNA was found in the IgA-positive compared with the IgA-negative fraction.