Epstein-Barr virus induced differentiation of early B-lineage cells

Transcription, translation and secretion of both IgA subclasses in polyclonally activated human lymphocytes

To analyze human IgA subclass-specific mRNA we have developed RNA probes for quantitation of alpha 1 and alpha 2 heavy chain constant region genes by solution hybridization. Under our assay conditions, we can detect as little as 3 pg of specific mRNA and there is less than 2% cross-reactivity between the two IgA subclasses. Using this method, the relative proportions of IgA1 and IgA2 mRNA in pokeweed mitogen (PWM)-stimulated cells were found to be 66% and 34%, respectively, while in the Epstein-Barr virus (EBV)-stimulated cells they were 77% and 23%, respectively. Cytoplasmic staining of the plasma cells and determination of IgA subclass distribution by flow cytometry revealed an almost even distribution of the two IgA subclasses as induced by both activators. The culture supernatant contained 72% IgA1 and 28% IgA2 after PWM stimulation, while EBV stimulation induced 85% IgA1 and 15% IgA2. This report thus describes a method for the quantitative analysis of IgA subclass-specific mRNA. Furthermore, we present evidence that in response to in vitro stimulation of peripheral blood lymphocytes by polyclonal activators the IgA-producing B cells not only synthesize both isotypes but also have the potential to secrete them.

Light-chain gene expression before heavy-chain gene rearrangement in pre-B cells transformed by Epstein-Barr virus

Epstein-Barr virus transformation of B-cell-depleted bone marrow cells from human fetuses allowed us to identify novel cell types characterized by the expression of immunoglobulin kappa or lambda light chain without heavy chains. Four kappa-only clones with normal karyotype were obtained and examined for their immunoglobulin gene configurations and expression. All four clones had kappa-chain gene rearrangements at either one or both alleles, but the heavy-chain gene loci in these clones either were in germ-line context or had undergone only D-JH rearrangements (D and JH represent diversity and joining gene segments). All clones contained kappa mRNA of normal size at levels consistent with the protein level, except for one clone that no longer produced kappa protein. No mu mRNA or immunoglobulin heavy-chain molecules were detected in any of the kappa+ clones. The results suggest that the mu heavy-chain protein is not an obligatory prerequisite for light-chain gene rearrangements.

Anti-immunoglobulin pretreatment induces a calcium-mobilization response to the chemotactic agent N-formylmethionylleucylphenylalanine in Daudi lymphoblastoid cells

Anti-immunoglobulin treatment of fura-2-loaded Daudi cells induces a calcium mobilization as judged by the increase in the fluorescence of the dye fura-2, AM. No calcium mobilization by N-fMet-Leu-Phe is observed in these cells. However, exposure of the cells to N-fMet-Leu-Phe after the first hit with anti-immunoglobulin (but not after soluble IgG) shows a rapid, dose-dependent calcium mobilization by N-fMet-Leu-Phe. The expression of the calcium-mobilizing response occurs in less than 2 min and is stable. Binding of tritiated N-fMet-Leu-Phe is increased in anti-immunoglobulin-treated but not control cells. The induction is specific for N-fMet-Leu-Phe because the chemoattractant platelet-activating factor did not induce any calcium mobilization. The N-fMet-Leu-Phe antagonist t-butoxycarbonyl-L-Phe-D-Leu-L-Phe-D-Leu-L-Phe- OH did not show any calcium mobilization on its own, either before or after anti-immunoglobulin treatment, and inhibited the calcium mobilization of N-fMet-Leu-Phe at low concentrations. Treatment of the cells with phorbol 12-myristate 13-acetate or pertussis toxin prior to anti-immunoglobulin treatment caused a dose-dependent abolition of both the anti-immunoglobulin-mediated calcium mobilization and the subsequent calcium mobilization by N-fMet-Leu-Phe. Metabolic inhibitors that act predominantly by lowering the ATP levels within the cell (iodoacetate, sodium fluoride, oligomycin, and 2-deoxyglucose) all produced a greater inhibition of the N-fMet-Leu-Phe-mediated calcium mobilization than the anti-immunoglobulin-mediated response. Lowering the temperature from 37 degrees C to 22 degrees C reduced the anti-immunoglobulin response and completely inhibited the expression of the N-fMet-Leu-Phe effect. Our results indicate that activation of the calcium-mobilization pathway in B cells by crosslinking of bound surface immunoglobulin causes an induction of N-fMet-Leu-Phe-sensitive calcium mobilization.

Epstein-Barr virus-transformed human precursor B cell lines: altered growth phenotype of lines with germ-line or rearranged but nonexpressed heavy chain genes

A series of lymphoblastoid cell lines (LCLs) have been established by in vitro infection of fetal bone marrow and fetal liver cells with Epstein-Barr virus (EBV). While most lines showed the usual mature B cell phenotype, a small proportion were cytoplasmic and surface immunoglobulin (Ig) heavy and light chain negative. Analysis of gene rearrangements indicated that the Ig- lines were either germ-line or nonproductively rearranged when probed for JH and were in germ-line configuration for C chi; no mu or chi mRNA could be detected in such cells. Precursor B cell lines were indistinguishable from their normal Ig+ counterparts in their expression of a wide variety of cell surface markers including "activation" antigens usually associated with the lymphoblastoid state; even the single LCL showing germ-line heavy and light chain genes expressed B lineage-specific cell surface antigens. However, the Ig- lines were distinct from their Ig+ counterparts in three important respects: (a) they grew much more slowly and achieved lower saturation densities, (b) they showed unusually high proportions (8-16%) of cells in EBV-productive cycle, and (c) they contained unusually high proportions (up to 40%) of cells expressing free joining (J) chain. These results suggest that precursor B cells differ in their response to the growth-transforming effects of EBV such that the virus-cell interaction in precursor B cell lines is inherently less stable than in conventional LCL. In particular there may be a greater movement of cells out of cycle and along the B cell maturation pathway. It is possible that such movement leads in individual cells either to virus replication or to a "sterile" plasmacytoid differentiation with J chain expression in the absence of Ig synthesis.