Use of an automatic cell harvester in a cellular radioimmunoassay

The conserved Cockayne syndrome B-piggyBac fusion protein (CSB-PGBD3) affects DNA repair and induces both interferon-like and innate antiviral responses in CSB-null cells

Cockayne syndrome is a segmental progeria most often caused by mutations in the CSB gene encoding a SWI/SNF-like ATPase required for transcription-coupled DNA repair (TCR). Over 43Mya before marmosets diverged from humans, a piggyBac3 (PGBD3) transposable element integrated into intron 5 of the CSB gene. As a result, primate CSB genes now generate both CSB protein and a conserved CSB-PGBD3 fusion protein in which the first 5 exons of CSB are alternatively spliced to the PGBD3 transposase. Using a host cell reactivation assay, we show that the fusion protein inhibits TCR of oxidative damage but facilitates TCR of UV damage. We also show by microarray analysis that expression of the fusion protein alone in CSB-null UV-sensitive syndrome (UVSS) cells induces an interferon-like response that resembles both the innate antiviral response and the prolonged interferon response normally maintained by unphosphorylated STAT1 (U-STAT1); moreover, as might be expected based on conservation of the fusion protein, this potentially cytotoxic interferon-like response is largely reversed by coexpression of functional CSB protein. Interestingly, expression of CSB and the CSB-PGBD3 fusion protein together, but neither alone, upregulates the insulin growth factor binding protein IGFBP5 and downregulates IGFBP7, suggesting that the fusion protein may also confer a metabolic advantage, perhaps in the presence of DNA damage. Finally, we show that the fusion protein binds in vitro to members of a dispersed family of 900 internally deleted piggyBac elements known as MER85s, providing a potential mechanism by which the fusion protein could exert widespread effects on gene expression. Our data suggest that the CSB-PGBD3 fusion protein is important in both health and disease, and could play a role in Cockayne syndrome.

Usefulness of a small scale indirect 125I-labelled protein A binding assay for detection of monoclonal antibodies against hematopoietic cell surface antigens

We describe a small-scale solid-phase indirect 125iodine protein A binding assay (IPA) and discuss its usefulness for detection of hematopoietic cell surface antigens and for screening hybridoma clones producing monoclonal antibodies (McAbs) against K562 cell surface antigens correlated with differentiation induced by 12-O-tetradecanoyl phorbol-13-acetate (TPA). This assay was performed in polystyrene Terasaki microtest plates instead of 96-well microtiter plates, using hematopoietic cells attached to the wells by air drying. This method facilitates washing procedures and reduces the radioactive waste. The specificity of this IPA method is as high as those of RIAs and ELISAs generally used. Titration curves of a McAb, My7, specific for CD13 on HL60 and TPA-treated HL60 (HL60-TPA) cells, were linear between the 10(-1) and 10(-4) dilutions. A difference in the CD13 expression between HL60 and HL60-TPA cells could be detected by both IPA and flow cytometry using My7 at 10(-1)-10(-3) dilutions. At the 10(-3) dilution, however, CD13 expressed on HL60 cells was detected by the IPA method but not by flow cytometry. These results show that the sensitivity of IPA is superior to that of flow cytometry. By screening hybridoma clones with this IPA method, we succeeded in producing three interesting and useful McAbs (21H73, 37G7 and 49C12) against K562 cell surface antigens whose expression was altered after the differentiation induced by TPA. We also demonstrated that the IPA method is suitable for cell surface marker analysis of leukemia cells freshly isolated from patients.

Strain differences in the expression of the Epa-1-restricting element

Epa-1-specific cytotoxic T lymphocytes (CTL) lyse epidermal cells (EC) of different Epa-1+ H-2k strains, such a AKR, CBA, C58, and RF, at different levels. We used an H-2Kk-specific monoclonal antibody (mAb) to test the hypothesis that this phenomenon is due to differences in the H-2-restricting element. Initially, we established the specificity of this mAb for the Epa-1-restricting element by demonstrating its capacity to inhibit the lysis of CBA EC by Epa-1-specific CTL. We then used it as the probe in a cellular radioimmunoassay to quantify the expression of the restricting element by EC of different H-2k strains. We found that C58 and RF EC bound significantly less of the mAb than did CBA EC. Although AKR also bound less of the mAb than did CBA EC, the difference was not statistically significant. To examine the generality of this phenomenon, we quantified the expression of Kk antigens on spleen cells (SC) of the same four strains. We found that RF SC, but not AKR or C58 SC, bound significantly less of the Kk mAb than did CBA SC. Thus, the differential CTL lysis of Epa-1+ EC of different strains probably reflects differences in expression of the H-2-restricting element rather than of the nominal antigen.

A new epitope of the T200 molecule family defined by the 3A35 monoclonal antibody and expressed by macrophages and activated T lymphocytes

A monoclonal antibody (mAb), 3A35, produced against mouse macrophages (M phi) was found to react against certain activated T cells. This mAb, a rat IgM, resulted from a cell fusion between a mouse plasmacytoma and rat lymphocytes immunized against mouse M phi. It bound more avidly to activated than to resident M phi. It did not react against B cells and resting T lymphocytes but recognized certain dividing T cells like EL4 lymphoma, concanavalin A-activated and interleukin 2-expanded spleen cells, and helper T cell hybridomas. By contrast, other T lymphocyte-derived cell lines such as YAC-1 and CTLL2 were unreactive. No clear relationship was found between the binding of 3A35 to cells and the expression of L3T4 and Lyt-2 antigens. The specific stimulation of T cell clones with antigen rapidly induced a strong reactivity with 3A35 mAb which declined thereafter to a low (helper clones) or non-reactivity (cytotoxic clones) after 10 days of culture. Immunoprecipitation experiments, performed with M phi derived from bone marrow cell cultures, surface iodinated with 125I or metabolically labeled with [35S]methionine, showed that 3A35 bound to a 200-kDa molecule, shifting to 175 kDa under reducing conditions. In peritoneal M phi activated in vivo, in addition to the 175-kDa band, new bands migrating at 140, 120 and 85 kDa were identified by 3A35 and could be absorbed on a commercial anti-T200 mAb bound to Sepharose beads. After strengthening the cell binding of 3A35 to EL4 lymphoma cells by a cross-linking agent, only a 85-kDa molecule was immunoprecipitated. Thus, 3A35 identifies a new epitope of the T200 molecule family which is expressed on M phi and activated T cells.

Solid-phase radioimmunoassay for the measurement of surface antigens expressed on intact lymphocytes

A solid-phase radioimmunoassay was developed for the measurement of lymphocyte surface antigens. The assay was performed in microplates, using cells that were initially fixed to the wells by air drying. The method was used for the measurement of Thy-1, Lyt-1,2,3, IL-2-R, H-2Kb and DR antigens on the surface of mouse thymus, spleen and bone marrow cells, mouse cell lines CTLL, EL-4 and DA-1 and human thymocytes and consisted of sequential incubations with rat or mouse monoclonal antibodies directed against the above antigens, rabbit anti-rat or goat anti-mouse IgG and 125I-protein A. The assay permits the processing of large numbers of samples, is easy to perform, reliable and highly specific.

Use of MTT colorimetric assay to measure cell activation

The MTT tetrazolium salt colorimetric assay previously described by Mosmann (1983, J. Immunol. Methods 65, 55) to measure cytotoxicity and cell proliferation was further explored to extend its application to the measurement of cell activation. The level of MTT cleavage by viable cells of various origins was found to be directly proportional to the number of cells but to increase as a non-linear function of time. This non-linear relationship was related to a time-linear cell death during MTT incubation. The cleavage of MTT by viable cells was found to follow first order kinetics and could be fitted to Michaelis' kinetics. Different cell types exhibited similar apparent Km values (1949 microM) and different apparent maximal velocities (V). The apparent V values determined for a given cell type under different experimental conditions were rigorously similar. This analysis of MTT cleavage by viable cells suggests that the colorimetric MTT test can be useful to quantify the activation level of cells, independently of proliferation.

Sustained IL-2 production by the EL4 subline during continuous phorbol diester stimulation is related to an increase of IL-2-mRNA

The murine T lymphoma EL4 subline produces large amounts of interleukin 2 (IL-2) upon stimulation with phorbol myristate acetate (PMA). It was found to survive continuous PMA stimulation (10 ng/ml, renewed daily, at 10(6) cells/ml), and to maintain its IL-2 production for several days in a culture medium low in protein. IL-2 production varied from day to day with a peak within the first 2 days of stimulation. PMA stimulation was accompanied by morphologic changes (enlargement and adhesiveness), arrest in cell division and DNA replication, continued RNA synthesis and increased mitochondrial activity. These effects were reversible upon removal of PMA, with a decrease of IL-2 secretion to the background level and a progressive recovery of cell growth. The reverted EL4 cells were again able to produce large amounts of IL-2 upon restimulation with PMA. Growth of EL4 cells was shown not to depend on autologous production of IL-2, and their DNA synthesis could be arrested by aphidicolin without a concomitant accumulation of IL-2 in the supernatant. This indicates that the increase in the amount of free IL-2 is not simply due to reduced consumption by the EL4 cells themselves. PMA appears to act at the level of the expression of the IL-2 gene, since IL-2 mRNA was much more abundant in the IL-2-secreting PMA-treated cells than in untreated controls. Our observations show that considerable amounts of IL-2 can be obtained from a single EL4 cell inoculum and may represent an original model to study the effects of PMA on the differentiation and maturation processes of cells.