Spleen samples of all ELMP2A transgenic animals were analyzed for surface expression of CD19 and IgM, two markers of mature peripheral B cells. genetically wild-type background. When crossed into a recombinase activating null (RAG?/?) genetic background, LMP2A expression in either RAG?/? ELMP2ABCR+ or RAG?/? ELMP2ABCR? animals was able to provide a survival transmission to BCR-negative splenic B cells. Additionally, bone marrow cells from all ELMP2A animals were able to proliferate in response to interleukin-7-dependent developmental signals in vitro. These studies illustrate that LMP2A can provide a survival transmission to BCR-negative B cells in two different groups of ELMP2A transgenic mice. Epstein-Barr computer virus (EBV) is able to infect primary human B cells in culture, transforming them into lymphoblastoid cell lines (LCLs). Upon contamination, the computer virus enters a latent life cycle characterized by the expression of six EBV nuclear antigens (EBNA1, EBNA2, EBNA3A, EBNA3B, EBNA3C, and EBNA-LP) and three latently expressed membrane proteins (LMP1, LMP2A, and LMP2B) (17). These latent viral proteins dramatically alter in vitro B-cell biology as characterized by upregulated expression of activation and adhesion markers (CD23, CD39, CD40, CD44, LFA-1, LFA-3, and ICAM-1), decreased dependence on high-serum medium, and secretion of immunoglobulin (17). However, EBV latency in defined culture systems in vitro is quite different from in vivo latency. In latently infected individuals, computer NS6180 virus can be isolated from immunoglobulin M-positive (IgM+) IgD? resting memory B cells which have lost surface expression of the costimulatory molecule B7-1 and the activation marker CD23 (1, 34, 35). Of the nine latent gene products detected in vitro, only EBNA1 and LMP2A transcripts are NS6180 reproducibly detected in latently infected human B cells (6, 34, 40, 46). Although latent computer virus has been isolated from peripheral B cells in normally healthy individuals Mbp (1, 6, 8, 15, 34, 35, 40, 46), latently infected B cells may reside in bone marrow or other lymphatic sites generating latently infected progeny cells which account for the stable quantity of infected peripheral B cells in normally healthy individuals (21, 23, 35, 50, 51). Considerable genetic and biochemical research has elucidated many aspects of LMP2A biology in vitro. LMP2A has 12 transmembrane domains and is expressed in patches on the surface of latently infected cells (24, 25, 42). The Lyn protein tyrosine kinase (PTK) binds to LMP2A via tyrosine residue 112 and is essential for the constitutive LMP2 phosphorylation detected in LCLs (12). Lyn-dependent phosphorylation allows other PTKs to bind NS6180 specific sites within the LMP2A amino terminal cytoplasmic tail (10, 12). The Syk PTK specifically binds to the LMP2A ITAM domain name at tyrosine residues 74 and 85 (11). Syk bound to LMP2A becomes constitutively phosphorylated and is unable to participate in B-cell receptor (BCR)-initiated transmission transduction (11). Through interactions with these and other cellular proteins, LMP2A is able to downmodulate intracellular NS6180 signaling cascades mediated by the BCR, the CD19 complex, and major histocompatibility complex class II (31, 33, 38). Although expressed in Hodgkin’s disease and nasopharyngeal carcinoma cells (2, 4, 7, 36, 37), LMP2A is not essential for EBV transformation in vitro (27C29). Transgenic mice expressing EBV latency proteins under transcriptional control of an immunoglobulin promoter have provided a convenient system for analyzing latent viral gene function in B cells in vivo. LMP1 transgenic mice develop lymphomas which exhibit upregulated expression of the antiapoptotic proteins Bcl-2 and A20, as well as the Myc oncoprotein (19). The episomal maintenance protein EBNA1 is able to induce monoclonal B-cell lymphomas in EEBNA1 transgenic mice (48, 49). These results are amazing in that EBNA1 has no transforming ability in vitro. Recently described research with ELMP2A transgenic mice suggest a role for LMP2A in B-cell survival in vivo (5). LMP2A transgene expression alters early B-cell development in the bone marrow during a transition requiring preBCR activation of Syk PTK. LMP2A expression blocks immunoglobulin heavy-chain expression while allowing subsequent immunoglobulin light-chain rearrangement. The producing peripheral B.
Spleen samples of all ELMP2A transgenic animals were analyzed for surface expression of CD19 and IgM, two markers of mature peripheral B cells