Model of Epstein-Barr virus infection of human thymocytes: expression of viral genome and impact on cellular receptor expression in the T- lymphoblastic cell line, HPB-ALL

Infection of B lymphocytes and epithelial tissue by Epstein-Barr virus (EBV) is associated with malignancy and autoimmunity. The cellular receptor for EBV has been identified as CD21 (CR2). A molecule, which is biochemically and immunologically similar to B-cell CD21, has been identified on a subpopulation of immature thymocytes, suggesting a role for this molecule in the regulation of T-cell development and further suggesting that immature T cells might be susceptible to EBV infection. A growing body of literature now documents the presence of EBV in tumors of T-cell origin. We have evaluated the susceptibility of the human immature T cell line, HPB-ALL, to infection by EBV. Electron microscopy studies showed a rapid internalization of virus by HPB cells. Southern blotting showed the intracellular presence of linear EBV genomes, and components of the virus replicative cycle were identified. Expression of the BamHI Z region of the genome, encoding the nuclear protein, ZEBRA, which is strictly associated with productive infection in B cells, was detected in HPB-ALL cells. A spliced variant of Z, RAZ, was also identified. Cell surface expression of EBV late antigens was observed to occur transiently. Infection of HPB cells was also accompanied by altered expression of T-cell surface molecules involved in antigen recognition, a process critical to normal development of the T-cell repertoire. Delineation of the outcome of T- cell infection by EBV may lead to a better understanding of the role of this virus in autoimmune processes and malignancy.     

Heterogeneity of the response of chronic lymphocytic leukemia cells to phorbol ester

The ability of the tumor promotor 12-0-tetradecanoylphorbol 13-acetate (TPA) to induce differentiation of leukemic cells was studied in 10 cases of chronic lymphocytic leukemia (CLL). An increase in modal volume and an enhancement of the capacity of te leukemic cells to stimulate in mixed lymphocyte reaction (MLR) was seen in the majority of cases. A significant increase in Ia expression was observed upon culture of leukemic cells with TPA in 6 of the 10 cases; 5 of these cases also showed an induction of cytoplasmic IgM production. Correlations between the phenotypic markers of the leukemic cells and their ability to respond to TPA were evaluated. CLL cells with low amounts to surface Ig. a volume less than or equal to 165 fl. and relatively low la expression responded well to TPA. Cells with bright surface Ig. a volume greater than or equal to 178 fl. and elevated amounts of Ia responded poorly to TPA. These results suggest that differences in the response of B leukemic cells to TPA reflect the underlying heterogeneity of the leukemic cells and might be correlated with their stage of maturation.     

Abnormalities of cytoplasmic Ca2+ in platelets from patients with uremia

Uremic patients have a hemorrhagic tendency, often associated with prolonged bleeding times and decreased platelet function in vitro. Whether these defects result from abnormalities in plasma factors affecting platelet activity, platelet surface receptors, intracellular platelet mediators, or other aspects of platelet behavior is unknown. To examine the possibility that the abnormality in platelet function may result from aberrations in Ca2+ homeostasis, blood was obtained from 29 patients with severe uremia. The platelets were washed, loaded with the Ca2+ -sensitive probes indo-1 and aequorin, gel-filtered, and resuspended in either plasma or buffer. Of the 29 patients, seven had template bleeding times prolonged to 11 minutes or more, but platelet aggregation in plasma was not consistently impaired in these patients. However, in aequorin-loaded platelets from the patients with long bleeding times, the highest elevation of cytoplasmic calcium [( Ca2+]i) in response to the Ca2+ ionophore A23187, arachidonate, adenosine diphosphate (ADP), or epinephrine was lower than that seen in platelets from both uremic patients with less prolonged bleeding times and normal volunteers. The reduced [Ca2+]i response was associated with decreased aggregation of gel-filtered platelets suspended in buffer. Suspending washed aequorin-loaded uremic platelets in normal plasma for 20 minutes did not reverse the decreased agonist-induced rise in [Ca2+]i; platelets from a normal donor resuspended in uremic plasma aggregated and produced a normal increase in [Ca2+]i in response to agonists. We conclude that the platelet defect seen in some patients with uremia is associated with a decreased rise in platelet [Ca2+]i after stimulation and that this is a manifestation of an intrinsic platelet defect.     

Functional interleukin-2 receptors are expressed on natural killer-like leukemic cells from a dog with cutaneous lymphoma

We identified a dog with large granular lymphocytic leukemia and cutaneous lymphoma that exhibited constitutive expression of interleukin-2 (IL-2) receptors by the leukemic peripheral blood lymphocytes. The leukemic cells phenotypically resembled natural killer (NK) cells, and their surface IL-2 receptors were functional, as determined by the capacity to bind human recombinant IL-2 with high- affinity resulting in the transduction of proliferation signals and in the development of lymphokine-activated killer cell activity. These cells produced IL-2 spontaneously, and they may have maintained their proliferative state through an IL-2-dependent autocrine growth pathway. Our results indicate that neoplastic lymphocytes of syndromes that involve circulating leukemic cells with dermotropism can originate from NK-like cells. Additionally, the data also suggest that proliferative conditions such as these may be the result of the aberrant production of IL-2. Further, this case illustrates the potential for the use of hematopoietic malignancies in the dog as a suitable animal model for immune targeting of IL-2 receptors as a novel treatment approach for similar malignancies of human beings.     

Two acquired immunodeficiency syndrome-associated Burkitt's lymphomas produce specific anti-i IgM cold agglutinins using somatically mutated VH4-21 segments

We analyzed the reactivity and the structure of the VH and VL segments of two IgM monoclonal antibodies (MoAbs) produced by spontaneously in vitro outgrowing cell lines, HBL-2 and HBL-3, established from two acquired immunodeficiency syndrome (AIDS) patients with Epstein-Barr virus (EBV)-negative Burkitt's lymphoma (BL). These B-cell clones were representative of the respective neoplastic parental clones, as determined by immunophenotypic and molecular genetic analysis. The IgM MoAbs were highly specific for the i determinant on red blood cells (cold agglutinins), but bound none of the other eight self and nine foreign antigens (Ags) tested, including those most commonly recognized by natural antibodies or autoantibodies. Structural analysis showed that the IgM MoAb VH segment sequences were 93.5% and 84.2% identical with that of the germline VH4-21 gene, which encodes the vast majority of cold agglutinins that are specific for the i/l carbohydrate Ag and are produced under chronic lymphoproliferative conditions. The HBL-2 MoAb VH4-21 gene segment was juxtaposed with 20P3 and JH6 genes and paired with a V lambda 1 segment, the sequence of which was 95.5% identical to that of the germline Humlv117 gene; the HBL-3 MoAb VH4-21 gene segment was juxtaposed with DXP'1 and JH5 genes and paired with a V lambda 1 segment, the sequence of which was 86.7% identical to that of the germline Humlv1L1 gene. The high degree of conservation of the VH4-21 gene in the human population, the nature of the nucleotide differences in the expressed VH4-21 segments, and the presence of nucleotide substitutions in the HBL-2 and HBL-3 IgM MoAb JH and/or J lambda segments suggested that the MoAb V segments underwent a process of somatic hypermutation. This was formally shown in the HBL-3 MoAb VH segment, by differentially targeted polymerase chain reaction amplification of the HBL-3 MoAb-producing cell genomic DNA. In addition, cloning and sequencing of the genomic DNA from fibroblasts of the same patient whose neoplastic B cells gave rise to the HBL-3 cell line yielded a germline copy of the VH4-21 gene. Thus, the expression of VH4-21 gene products may be involved in a self Ag-driven process of clonal B-cell expansion and selection associated with BL in these AIDS patients.     

Tumor necrosis factor-alpha downregulates protein S secretion in human microvascular and umbilical vein endothelial cells but not in the HepG- 2 hepatoma cell line

Protein S deficiency, which is associated with thrombosis, can either be inherited or acquired. Recently, we reported that a decrease in free protein S was observed in 19 of 25 persons with HIV/AIDS. The proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), has been reported to be elevated in human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients and has been shown to induce a procoagulant state on the surface of endothelial cells. We report here that recombinant TNF-alpha (rTNF-alpha) downregulated protein S synthesis in the SV-40T transfected human microvascular endothelial cell line (HMEC-1) model system by approximately 70% and in primary human umbilical vein and dermal microvascular endothelial cell cultures by approximately 50%. Using the HMEC-1 model, Northern blot analysis showed a decrease in protein S RNA at 24 hours that was corroborated by Western blot analysis and enzyme- linked immunosorbent assay (ELISA) quantification. Evidence supporting the specificity of the TNF-alpha effect included the following: (1) TNF- alpha down-regulation of protein S was completely blocked by TNF neutralizing antibody; (2) the effect was transient, and protein S was restored to near normal levels after TNF was removed from cell cultures; (3) an antibody directed to the TNF RI (55-kD receptor) was shown to mimic the action of TNF-alpha on HMEC-1 cells; and (4) other proinflammatory cytokines, interleukin (IL)-1, IL-6, and TGF-beta, had no effect on protein S secretion. However, TNF-alpha showed no regulatory control over protein S synthesis in the human hepatocellular carcinoma cell line HepG-2. We suggest that TNF-alpha downregulation of protein S may be a mechanism for localized procoagulant activity and thrombosis recently reported in some AIDS patients with associated protein S deficiency.     

A 16-channel SQUID-device for biomagnetic investigations of small objects

Biomagnetic investigations in basic physiological research using animals require measurement devices different from commercial biomagnetometers used in human investigations. Two major problems have to be tackled in the design of such biomagnetometers. First, the spatial sampling needs to be much higher. Second, the distance between pick-up coils and the sources needs to be much shorter in order to compensate the worse signal-to-noise ratio (SNR) due to the smaller pick-up coils. We designed and built a 16-channel biomagnetic measurement system meeting these design criteria. The pick-up coil diameter of this new biomagnetometer is 6.7 mm, thus allowing 16 channels on an area of 3.2x3.2 cm2. The pick-up coils are located 3 mm above the dewar outer bottom, hence the closest distance to the cortical surface can be a few millimetres. We provide as an example of first measurements performed with the new biomagnetometer investigations of epileptic spikes in adult rabbits by simultaneous magnetoencephalogram (MEG) and electrocorticogram (ECoG) recordings. The high SNR of the recorded MEG and the simultaneously detected electric potentials allow investigations of the spatio-temporal pattern of neuronal processes of epileptiform spikes with signal strengths of about 3.5 pT.