Selective release of excreted DNA sequences from phytohemagglutinin-stimulated human peripheral blood lymphocytes. Effects of trypsin and divalent cations

Extracellular DNA Level in the Blood of Irradiated Rats

There is high-molecular DNA in the blood of unirradiated rats which moves as a single fraction during electrophoresis in 0.5% agarose. At short times (2-5 h) after gamma-irradiation at doses from 1 to 100 Gy a low-molecular species of DNA appears (about 180 nucleotide pairs), the amount of which is directly proportional to exposure dose at 5 h after exposure. It has been established by Southern hybridization that the low-molecular DNA has few nucleotide sequences common with those of the high-molecular DNA, but it shows homologously to genomic sequences.

The origin of elevated levels of circulating DNA in blood plasma of premature neonates

The relationship between the concentration of cell-free DNA (cfDNA) and the number of proliferating/apoptotic lymphocytes in peripheral blood of premature newborns of different gestation age and full-term newborns was determined. The experiments were performed using fluorescent spectrophotometry (with Hoechst 33342), flow cytometry, and microscopy (Feulgen staining of lymphocytes). It was determined that the lymphocyte population of premature newborns may consist of 4.6% of proliferating and 22.1% apoptotic cells. For full-term newborns, the percentage was 2.5% and 2.9%, respectively. A direct correlation between the concentration of extracellular DNA and the number of proliferating lymphocytes of full-term newborns was ascertained (r= 0.400; P < 0.05). For premature newborns, the concentration of extracellular DNA correlated both with proliferating lymphocytes and apoptotic cells. The results show that premature birth causes the induction in lymphocytes of both apoptosis and proliferation that are accompanied by an increased extracellular DNA concentration in the blood of newborn babies.

DNA binding to mouse cells is mediated by cell-surface molecules: the role of these DNA-binding molecules as target antigens in murine lupus

Autoimmunity to a 28-29-kDa cell-surface DNA-binding molecule has previously been described in patients with systemic lupus erythematosus and related autoimmune diseases. This report describes experiments that implicate a similar antigen-antibody system in the evolution of autoimmunity in lupus-prone mice. DNA binding to murine spleen cells was found to be a saturable phenomenon that was inhibited by excess cold DNA and trypsinization. The role of autoimmunity to murine cell-surface DNA-binding molecules in lupus-prone mice (MRL lpr/lpr, MRL +/+, BXSB) was compared to normal mice (BALB/c, C3H.SW) by means of an assay that measured the inhibition of cell-surface DNA binding. Only sera from lupus strains had inhibitory activity and this component was shown to be an IgM autoantibody. Furthermore, we isolated a spontaneously occurring IgM monoclonal antibody from the spleen of an MRL/lpr mouse, which inhibited DNA binding to mouse cells. Time-course studies indicated that young female MRL/lpr mice lacked detectable activity against cell-surface DNA-binding molecules; however, by 8-10 weeks maximal inhibitory activity was observed. This response occurred prior to the development of significant antinuclear antibody activity. With the appearance of overt disease and anti-DNA antibodies, inhibition of DNA-binding activity became undetectable. These findings mirror previous studies on autoimmunity to a cell-surface DNA-binding molecule on human leucocytes, but have the added advantage of permitting the study of the temporal evolution of this inhibitory activity in relation to disease expression.

Identification of a cell-surface DNA receptor and its association with systemic lupus erythematosus

We have previously reported the existence of a cell-membrane-associated molecule on human PBMC, which binds DNA and has the characteristics of a receptor. Monoclonal antibodies have been made to this receptor and have been used successfully for the purification of this cell-surface molecule. Preliminary studies have indicated a receptor for DNA on murine kidney and spleen cells which is similar in molecular weight to the human DNA receptor (30 kD). The occurrence of autoantibodies to cell-surface receptors has been described in several autoimmune diseases and we have noted that the serum of patients with lupus and similar disorders inhibit the binding of labeled DNA to human leukocytes. Using a "dot-blot" assay with affinity-purified human DNA receptor, sera from patients with various CTD and from healthy volunteers were screened for anti-receptor antibodies; anti-receptor antibodies were found in many patients with CTD and some of their first-degree relatives. The prevalence of anti-receptor antibodies in normal blood donors was less than 2%. It is hypothesized that anti-receptor antibodies represent an early immune response in lupus and kindred disorders and that anti-DNA antibodies may arise from the corresponding anti-idiotypic response.

Lactoferrin binds to neutrophilic membrane DNA

Lactoferrin (LF) binding to the surface of human neutrophils was shown to be dependent upon the presence of cell surface DNA by (i) an abrogation of LF binding after treatment of whole cells with DNAse; (ii) an abrogation of LF binding to a purified cell membrane suspension after DNAse digestion, (iii) a restoration of LF binding, after initial treatment of cells with DNAse, by the addition of exogenous DNA. Using a biotinylated LF probe, no other binding molecules were found after SDS PAGE of neutrophil cell membrane proteins. Further evidence of a DNA-LF interaction was obtained by the co-isolation of LF with DNA by both gel chromatography and affinity chromatography using Heparin Sepharose CL 6B. The interaction of LF with neutrophils was a saturable phenomenon with a Kd of 6.2 X 10(-6) M and a maximum binding of 9.2 X 10(6) molecules per cell. These results suggest that cell membrane DNA may have a novel role as a receptor for LF, and indicates the need for further experiments to determine whether the functional effects of LF are modified by the DNAse treatment of LF responsive cells.

DNA binding to human leukocytes. Evidence for a receptor-mediated association, internalization, and degradation of DNA

Previous studies have indicated that white blood cells possess DNA on their outer membranes. In this study we set out to determine whether exogenous DNA bound to cells in a fashion compatible with a ligand receptor union. Purified populations of white blood cells; neutrophils (polymorphonuclear leukocytes, PMN), adherent mononuclear cells (ADMC), rosetting lymphocytes (E+ cells), and nonrosetting lymphocytes (E- cells) were incubated with radiolabeled lambda phage DNA in increasing concentrations. Binding of [3H]DNA was a saturable process and was inhibited by excess cold DNA and prior trypsinization of the cells. Rate zonal density centrifugation of purified cell membrane preparations confirmed that DNA was binding to the outer cell surface. The dissociation constant for all four cell types was approximately 10(-9) M, and from 0.81 X 10(3) to 2.6 X 10(3) molecules of lambda phage DNA bound to each cell depending upon cell type. Binding was not competitively inhibited by RNA, polydeoxyadenylic acid-polydeoxythymidylic acid (poly [d(A).d(T)]), or mononucleotides. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE)-separated proteins from PMN, ADMC, E+, and E- cells were electrophoretically blotted onto nitrocellulose sheets; a probe of biotin-labeled DNA indicated a single species of DNA-binding molecule migrating in a position consistent with a molecular weight of 30,000. Isotopic and immunofluorescent studies indicate that DNA is internalized and degraded to oligonucleotides; this process is inhibited by cycloheximide. These results support the notion that there is a common binding site for DNA on white blood cells, that the stoichiometry of the association is compatible with a ligand receptor relationship, and that this apparent receptor is responsible for the endocytosis and degradation of exogenous DNA.

RISH IV. Immunoglobulin diversity

RISH considers that cell surface components involved in like cell identification are not involved in the structure of the plasma membrane per se and are attached to a part of their mRNA. the mRNA then acts as a template for the synthesis of DNA. Thus the component at the cell surface is attached to an RNA/DNA receptor. If there is a conformational change in the component (antigen) this will cause a distortion in its RNA/DNA receptor. This distortion is then detected by a tissue specific T lymphocyte which removes all or part of the RNA/DNA receptor from the aberrant cell and the lymphocyte then undergoes replication. During this process receptor RNA/DNA is incorporated into the daughter lymphocyte which becomes a B lymphocyte/plasma cell producing immunoglobulin. The initial tissue specific T lymphocyte becomes a dual functional helper/suppressor cell. The B lymphocytes use the RNA from the RNA/DNA receptor to synthesize the variable region of the first antibody, IgM1. This antibody (IgM1) does not react with the antigen, ie. the distorted component, or the receptor RNA, but with receptor DNA. The DNA of the receptor base pairs with its complementary strand in the B lymphocyte, and the complementary DNA acts as a template for mRNA synthesis. This results in the production of IgM2 and IgG that can bind the antigen and receptor RNA. These antibodies (IgM1, IgM2 and IgG) when endocytosed by the stimulating cell will also complex cytoplasmic mRNA and nuclear DNA and prevent the synthesis of the antigen that initiated the immune response. If other classes of antibodies are to be produced they will follow a similar pattern (IgM1, IgA and IgG or IgM1, IgE and IgG). From the codons of the known amino acids, the codons for amino acids from translation of the complementary DNA strand have been calculated. The amino acids derived from the complementary codons are considered to represent sequences of amino acids in the antigen as represented by the DNA of an RNA/DNA receptor. For these sequences of amino acids, each has a complementary amino acid as defined by the normal codon. These complementary amino acids are then used in the synthesis of the variable region of the antibody.

Strategies for detection of transfusion-transmitted viruses eluding identification by conventional serologic tests. II. Detection of host DNA in human plasmas with elevated alanine aminotransferase

As a prelude to the development of nucleic acid probes specific for non-A, non-B hepatitis virus(es) (NANBV), plasmas with alanine aminotransferase levels greater than or equal to 110 IU were assayed for DNA by a radioimmunoassay. Approximately 50% of such plasmas are expected to contain NANBV. One-hundred and seventy-eight of 420 plasma samples tested (42.4%) contained sequestered DNA resistant to DNAse I. The DNA has a molecular weight of approximately equal to 0.8 to 1.4 X 10(6) daltons and hybridizes with a 32P-labeled human DNA probe. The DNA in plasma is mostly bound to IgM. The presence of host DNA will have to be taken into account in planning experiments aiming at the preparation of nucleic acid probes specific for NANBV using infected plasmas as source material. Such experiments will have to utilize recombinant DNA technology and will require the separation of bacterial colonies containing recombinant DNA with viral DNA sequences from colonies with human DNA inserts. The feasibility of this approach is demonstrated using plasma-containing hepatitis B virus.

Centrifugal elutriation of human lymphoid cells: synchronization and separation of aneuploid cells into diploid and tetraploid populations

Both normal and leukemic human lymphoid cell lines were separated into populations corresponding to different positions in the cell cycle by centrifugal elutriation. Each population was analyzed for cell concentration, cell volume, [3H]thymidine incorporation, percentage S phase by autoradiography, and percent G1, S, and G2/M phases by flow cytometry. The smallest cells, collected at the lowest flow rate, were in G1 phase. Cells collected at increasing flow rates progressively increased in volume and represented distinct positions in the cell cycle transition from G1 phase, through S phase, and into G2/M phase. The purity of the G1 population varied according to cell load. One hundred percent of cells were recovered and cells collected in G1- and S-phase populations proliferated in culture with patterns characteristic of synchronized cells. An aneuploidy leukemia cell line, CEM, was separated into near-diploid and near-tetraploid populations by centrifugal elutriation. This method of cell separation provides large numbers of human lymphoid cells at different positions in the cell cycle for investigating the relationship between the cell cycle and various surface membrane and metabolic properties of cells. Aneuploid leukemia and lymphoma cells can be separated by centrifugal elutriation into populations which contain different numbers of chromosomes for comparisons of their biologic properties.

Lactoferrin binds to cell membrane DNA. Association of surface DNA with an enriched population of B cells and monocytes

The binding of human 125I-labeled lactoferrin (LF) to a population of adherent mononuclear cells (ADMC) and nonrosetting lymphocytes (E-) was abolished by prior treatment of the cells with deoxyribonuclease (DNase), but not ribonuclease (RNase). When DNase-treated ADMC were incubated with exogenous DNA, the binding of 125I-LF was restored. Enzymatic digestion with other enzymes, trypsin, phospholipase D, and neuraminidase, did not significantly influence 125I-LF binding. Saturable binding of LF at 0 degrees C was demonstrated for both E- and ADMC, with equilibrium dissociated constants of 0.76 x 10(-6) M and 1.8 x 10(-6) M, respectively. E- cells bound 2.5 x 10(7) and ADMC bound 3.3 x 10(7) molecules of Lf at saturation. Cell membranes were isolated from ADMC, E- and E+ and reacted with 125I-labeled LF; significant binding was only seen with ADMC and E-. Prior treatment of the membranes with DNase abolished the binding. Immunofluorescence studies indicated that a population of ADMC and E-, but not E+, exhibited a peripheral staining pattern for LF. Prior treatment of ADMC and E- with DNase abolished the surface immunofluorescence. This study provides evidence that cell membrane DNA acts as a binding site for exogenous LF. This is a novel role for DNA that has not been previously reported. Furthermore, it points to a basic difference between E+ cells vs. ADMC and E- cells in respect to their possession of cell surface DNA.

Effect of mitogen concentration on glucocorticoid suppression of normal and cystic fibrosis lymphocyte activation

It has previously been demonstrated that glucocorticoid suppression of mitogen-induced lymphocyte activation is a function of mitogen dose. Glucocorticoids suppress lymphocyte activation more at low doses, which induce suboptimal lymphocyte activation, than at higher doses which are optimal for lymphocyte activation. This observation suggests that glucocorticoid suppression of lymphocyte activation might be greater than normal in disease states which are associated with depressed mitogen-induced lymphocyte activation. To test this hypothesis, lymphocytes from normal individuals and patients with cystic fibrosis were activated by a full range of concentrations of concanavalin A (Con A) in the presence or absence of dexamethasone. Con A activation of cystic fibrosis lymphocytes was markedly depressed compared to the activation of normal lymphocytes at all doses of Con A, but the suppressive effect of dexamethasone on the activation of normal and cystic fibrosis lymphocytes was the same. We conclude that glucocorticoid suppression of lymphocyte activation is more a function of mitogen dose than of the level of lymphocyte activation and is not necessarily greater than normal in disease states which are associated with depressed mitogen-induced lymphocyte activation.

Unstable high molecular weight inverted repetitive DNA in human lymphocytes

About 1% of newly synthesized DNA from PHA-stimulated human lymphocytes can be isolated as large (up to 90 kilobase pairs) double stranded fragments that resist sequential alkali and heat denaturation steps but are not closed circular. By electron microscopy about 1% have single-strand hairpin loops at one end and therefore present inverted repetitive sequences (IR-DNA). Most of the remainder have a blunt-appearing double-strand terminus at both ends (78%) or one end (18%). Indirect evidence indicates that these also are inverted complementary structures with terminal hairpin loops too small to be visualized: (1) Treatment with either a 5' or 3' single-strand exonuclease generates essentially only fragments with a single strand at one end; (2) with partial denaturation, the number of fragments with identifiable single-strand hairpin loops increases (to about 20%); (3) after S1 nuclease digestion, greater than 95% can be fully heat denatured. Cot analysis indicates that these fragments are derived from dispersed sites throughout the genome. Up to 25% of DNA released from lymphocytes during growth similarly resists denaturation, and released DNA and IR-DNA are both enriched in the same set of repetitive sequences. Thus at least a portion of IR-DNA appears to be unstable.

Persistence of cells capable of T-cell growth factor production in long-term human t-lymphoblast cultures

Human T-lymphoblasts maintained in culture for 1-2 months in T-cell growth factor conditioned medium continue growth when placed in fresh culture medium in the presence of phytohemagglutinin and irradiated adherent cells. In the absence of lectin, no growth occurs. Neither long-term cells nor irradiated adherent cells plus lectin produce soluble factors that stimulate long-term cell growth, but small amounts of this biologic activity can be detected in the culture medium when the two cell sets are mixed together. The data indicate that human long-term cell populations retain the ability to make enough TCGF to stimulate proliferation, but require physical contact with monocytes in the presence of phytohemagglutinin for this response to occur.

Quantitation and characterization of plasma DNA in normals and patients with systemic lupus erythematosus

Using the in vitro DNA labeling technique of nick translation on purified plasma DNA, we have estimated the plasma DNA concentration in three normal individuals to be 266 +/- 57 ng/ml (mean +/- SD). This was not significantly different in three patients with a chronic inflammatory disease (209 +/- 14 ng/ml) or in five patients with steroid-inactivated systemic lupus erythematosus (SLE) (293 +/- 57 ng/ml). In two untreated, newly diagnosed, active SLE patients, however, the plasma DNA concentration was considerably higher (4,024 and 2,437 ng/ml, respectively). Characterization of these in vitro labeled DNA preparations by neutral sucrose-gradient sedimentation analysis showed a sedimentation coefficient of 6-8S, corresponding to a molecular weight of similar to or approximately 0.2-0.45 x 10(6). No difference was observed between normal subjects or patients. In addition, the relative size uniformity of these DNA molecules might suggest some form of specific protection of the DNA from blood DNAases. Further characterization in terms of buoyant density in cesium chloride did not reveal a difference between normal or SLE plasma and the human (HEp-2 cell) DNA used as marker. Taking into account the limitations of the method, no indication of a possible exogenous origin of the DNA circulating in SLE patients could be found. The physiological or pathophysiological role of this plasma DNA remains to be determined.