Chronic lymphocytic leukemia (CLL) cells express the receptor for Epstein-Barr virus (EBV) and can be infected in vitro. Infected cells do not express the growth-promoting set of EBV-encoded genes and therefore they do not yield LCLs, in most experiments. With exceptional clones, lines were obtained however. We describe a new line, HG3, established by in vitro EBV-infection from an IGHV1–2 unmutated CLL patient clone. All cells expressed EBNA-2 and LMP-1, the EBV-encoded genes pivotal for transformation. The karyotype, FISH cytogenetics and SNP-array profile of the line and the patient's ex vivo clone showed biallelic 13q14 deletions with genomic loss of DLEU7, miR15a/miR16–1, the two micro-RNAs that are deleted in 50% of CLL cases. Further features of CLL cells were: expression of CD5/CD20/CD27/CD43 and release of IgM natural antibodies reacting with oxLDL-like epitopes on apoptotic cells (cf. stereotyped subset-1). Comparison with two LCLs established from normal B cells showed 32 genes expressed at higher levels (> 2-fold). Among these were LHX2 and LILRA. These genes may play a role in the development of the disease. LHX2 expression was shown in self-renewing multipotent hematopoietic stem cells, and LILRA4 codes for a receptor for bone marrow stromal cell antigen-2 that contributes to B cell development. Twenty-four genes were expressed at lower levels, among these PARD3 that is essential for asymmetric cell division. These genes may contribute to establish precursors of CLL clones by regulation of cellular phenotype in the hematopoietic compartment. Expression of CD5/CD20/CD27/CD43 and spontaneous production of natural antibodies may identify the CLL cell as a self-renewing B1 lymphocyte.

Following infection with Epstein-Barr virus (EBV), the virus is carried for life in the memory B-cell compartment in a silent state (latency I/0). These cells do not resemble the proliferating lymphoblastoid cells (LCLs) (latency III) that are generated after infection. It is of fundamental significance to identify how the different EBV expression patterns are established in the latently infected cell. In view of the prompt activatability of CD4 + T cells in primary EBV infection, and their role in B-cell differentiation, we studied the involvement of CD4 + T cells in the regulation of EBV latency. Lymphoblastoid cell lines (LCLs) were cocultured with autologous or allogeneic CD4 + T cells. Activated T cells influenced the expression of two key viral proteins that determine the fate of the infected B cell. EBNA2 was down-regulated, whereas LMP1 was unregulated and the cells proliferated less. This was paralleled by the downregulation of the latency III promoter (Cp). Experiments performed in the transwell system showed that this change does not require cell contact, but it is mediated by soluble factors. Neutralizing experiments proved that the up-regulation of LMP1 is, to some extent, mediated by IL21, but this cytokine was not responsible for EBNA2 down-regulation. This effect was partly mediated by soluble CD40L. We detected similar regulatory functions of T cells in in vitro-infected lymphocyte populations. In conclusion, our results revealed an additional mechanism by which CD4 + T cells can control the EBV-induced B-cell proliferation.infectious mononucleosis | Hodgkin lymphoma F ollowing primary EBV infection, the virus is carried by its human host over a lifetime. In healthy individuals, the latent virus resides in the memory B-cell compartment (1), in cells that do not resemble the proliferating lymphoblastoid cells (LCLs) generated by in vitro infection. The carrier cells usually do not express any virally encoded proteins other than EBNA1, which is required for the maintenance of the viral episomes. They do not express the growth transformation program and have a resting phenotype and, therefore, do not represent a direct pathogenic threat.The establishment of this type of latency by EBV is a focal point of attention, ever since the virus was discovered. According to one scenario, EBV exploits the B-cell differentiation program (2). The virus infects naïve IgD + B cells that subsequently express 9 virally encoded proteins (EBNA1 through -6 and three LMPs) and transforms the cells into immunoblasts. This expression pattern is referred to as the "growth transformation," or latency III program. The key proteins of this program are EBNA2 and LMP1. Because at least six of the nine proteins are immunogenic, the proliferating immunoblasts are readily recognized and eliminated by immune effector cells. A fraction of the infected cells migrate to the lymph node follicles and concurrently change their viral transcription program to express only three proteins: EBNA1, LMP1, and LMP2 (latency II). The LMPs facili...

The potentially oncogenic Epstein-Barr virus (EBV) is carried by almost all humans in a well equilibrated coexistence. The phenotype of the cells that carry EBV genomes is determined by virally-encoded and cellular proteins. B lymphocyte is the main target of the virus and latent infection of this cell induces proliferation. Nine virus-encoded genes participate in the “growth program” that is expressed in a narrow differentiation window of the B cell. Such cells have the potential to develop malignant proliferations. However, several control mechanism eliminate this danger and the general chronic virus carrier state is most often asymptomatic. One mechanism exploits the normal regulation in the immune system, the T cell mediated modulation of the B cell differentiation state. Another is based on cognate recognition and elimination of the infected cells. The expression of EBV encoded genes in B lymphocytes can be also “restricted,” they do not express all components of the viral growth program. Here, we discuss a rare viral expression in B cells that has not been connected with malignant transformation yet.

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