Comparison between dissociation and inhibition of association of DNA/anti-DNA complexes

A study was made of the increases in ionic strength (mu) and in pH that would effect: a) the inhibition of association of anti-double stranded (ds) DNA and dsDNA, and b) the dissociation of anti-dsDNA from dsDNA, with respect to high avidity as well as to low avidity human anti-dsDNA antibodies, using Crithidia luciliae kinetoplasts as a source of dsDNA. The results obtained appear to indicate that the electrostatic component of the antigen-antibody bond does not become stronger with time (for times spans less than 1 hr).

Prognostic value of anti-dsDNA in SLE

In a prospective longitudinal study 130 patients with systemic lupus erythematosus (SLE) were studied at least monthly for a relationship between the anti-dsDNA levels and disease activity. We observed 13 patients who developed 15 periods of exacerbations of their disease. All 15 exacerbations were preceded by a continuous increase of the anti-dsDNA levels. In 13 of the 15 exacerbations studied the exacerbation was preceded by an increase of anti-dsDNA with a doubling time (T2) of less than 6 weeks; in 4 of the 5 other exacerbations the T2 was less than 10 weeks. Four other patients with an increase of the anti-dsDNA levels showed no exacerbation. In these 4 patients the T2 was larger than 10 weeks. The other 113 patients did not show an increase of anti-dsDNA over the 2 years of monitoring and showed no signs of serious disease activity (no major symptoms). These observations suggest that an SLE patient who is followed up frequently and who shows a continuous increase of anti-dsDNA witha T2 shorter than 10 weeks is bound to develop an exacerbation.

Detection of anti-dsDNA as diagnostic tool

The diagnostic significance of anti-dsDNA determinations was evaluated in 2 different groups of patients. When the immunofluorescence technique (IFT) with Crithidia luciliae and the Farr assay with 3H-labelled-PM2 DNA were applied to a selected panel of 536 sera from patients with various well-defined autoimmune diseases, positive results were obtained only with serum samples from patients with systemic lupus erythematosus (SLE). On the other hand when we screened 4431 sera sent to our laboratory for diagnostic reasons, we observed a high incidence of antibodies to dsDNA in patients who did not fulfil the preliminary American Rheumatism Association's criteria for SLE and did not have the diagnosis SLE. Furthermore, a significant number of the positive sera showed peculiar behaviour in that they were positive only in the IFT on Crithidia luciliae and not in the Farr assay.

Ratio-dominance model of suppression: an analysis by limiting dilution

A theoretical framework is presented which explores two models of suppressor cell-target cell interactions in T-dependent antibody responses. The first is the full-dominance model, in which a single or limited number of suppressor cells can entirely suppress an immune response irrespective of the multiplicity of other effector cells present. The second is the ratio-dominance model, in which a suppressor cell is capable of inactivating only a certain number of target cells. Thus, the multiplicity of target cells in a given microculture well influences the degree of suppression. Both models are evaluated using limiting dilution analysis and two systems are explored. In the first model, suppressor cells alone are titrated into microculture wells containing all other cells required for an immune response. In the second, suppressor cells are added from populations containing a mixture of helper T cells as well as suppressor cells. This latter type of analysis is similar to that in which populations of T cells primed to alloantigens in mixed lymphocyte cultures are analysed for positive (help) and negative (suppression) allogeneic effects. The analysis allows us to conclude that such suppressor cells operate via a mechanism best described by a ratio-dominance model.

Dissociation of DNA/anti-DNA complexes at high pH

A high-avidity human antibody (Ab) to double-stranded DNA (dsDNA) could be virtually completely dissociated from Crithidia luciliae kinetoplast dsDNA at pH 12 and a low-avidity Ab at pH 11. At low pH (pH 2), no dissociation occurs of either Ab. Low-avidity Ab could be dissociated at neutral pH with 1 M NaCl, but even with 5 M NaCl high avidity Ab could not be dissociated. Prolonged exposure to pH 12 did not affect DNA-binding by Ab after dialysis against PBS. A decrease in surface tension of the liquid medium in no case prompted dissociation. Contact angle measurements on DNA showed it to be very hydrophilic. It is concluded that concomitant with the strong negative charge of the antigen and the positive charge of the Ab, both antigenic determinant and antibody-active site are exceptionally hydrophilic, which causes their van der Waals attraction in aqueous media to be negligibly small. This particular antigen-antibody bond thus is mainly electrostatic and can be completely dissociated by abolishing the positive charge of the antibody-active site through a drastic increase in pH.

Anti-dsDNA and complement profiles as prognostic guides in systemic lupus erythematosus

Antibodies to dsDNA, tested with circular DNA in the Farr assay, are specific for systemic lupus erythematosus. A longitudinal study showed a clear relation between the clinical state, the anti-dsDNA titer (expressed in units), and the C1q and C3 levels: when anti-dsDNA levels remained high, no exacerbations were observed. A sharp drop in anti-dsDNA, usually preceded by a rise, was related to a serious exacerbation. Only during the exacerbation when both C1q and C3 were very low was renal involvement seen.

The purification and quantitation of helper T cell-replacing factors secreted by murine spleen cells activated by concanavalin A

A microculture assay with low numbers of athymic (nude) spleen cells has been used to quantitate the helper T cell-replacing activity secreted by concanavalin A-treated spleen cells. This quantitation allows an estimate of the recovery of biologic activity during concentration from culture supernatants by salt precipitation, and purification by gel filtration, ion exchange chromatography, and isoelectric focusing. The T cell-replacing activity is found in protein of 30 to 40,000 daltons size as estimated by gel filtration, but shows heterogeneity in electric charge. The activity is active at concentrations of less than 10(-9) M, and is strictly antigen dependent in its mode of action.

Immunology of DNA. VI. The effect of mercaptans on IgG and IgM anti-dsDNA

Reduction of IgM antibodies to DNA with mercaptans such as dithioerythrol or 2-mercaptoethanol completely destroys DNA binding in the Farr assay and in the immunofluorescence technique by Crithidia luciliae. In contrast reduction of IgG antibodies to DNA results in a six-fold increase of DNA binding in the Farr assay while no effect on titres in the immunofluorescence technique can be observed. Our results lead to the following conclusions: 1) The Farr assay is selective for high avidity interactions; only a minor part of IgG antibodies to DNA is measured; 2) 7S IgM antibodies to DNA cannot be demonstrated in the Farr assay or the immunofluorescence technique; obviously only multivalent interactions, as obtained with the intact 19S IgM molecule are stable in these assays; 3) reduction of IgG leads to a greater flexibility of this molecule; this facilitates monogamous bivalent binding to DNA; 4) THE PRESENTATION OF DNA in the kinetoplast of Crithidia luciliae favours a monogamous bivalent binding of antibodies to DNA with high avidity; this accounts for occasionally observed discrepancies between anti-DNA activity in the Farr assay and in the immunofluorescence technique.

Immunology of DNA. V. Analysis of DNA/anti-DNA complexes

DNA/anti-DNA complexes were studied by equilibrium density centrifugation in CsC1 and by zonal centrifugation in sucrose gradients. Complexes prepared of circular DNA preparations PM2 DNA or SV40 DNA with anti-DNA obtained from patients with systemic lupus erythematosus were found to be stable under the conditions of CsC1 equilibrium centrifugation. This enabled homogeneous complexes of DNA and anti-DNA of composition AgAb1, AgAb2, AgAb3 etc to be isolated. The stability of these complexes, their banding pattern in CsC1 gradients and their sedimentation behaviour suggest that anti-DNA binds to DNA in a monogamous bivalent way.

Immunology of DNA. IV. Quantitative aspects of the Farr assay

We have investigated whether the Farr assay measures the primary interaction between DNA and anti-DNA. By the use of zonal centrifugation to analyse DNA/anti-DNA complexes and by a detailed study of the quantitative aspects of the Farr assay we demonstrate that: (a) binding of a single IgG molecule to a PM2 DNA molecule (molecular weight 5.9 X 10(6)) renders the latter precipitable in half-saturated ammonium sulphate; (b) two antibody molecules are required for precipitation of T7 DNA (molecular weight 25 X 10(6)); (c) millipore filtration detects binding of a single antibody molecule per molecule of PM2 DNA; (d) theoretically and experimentally the relation between free DNA (F) and the amount of serum (S) can be described by IfF =-cS where c is a constant; (e) it is feasable to quantitate serum anti-DNA activity in terms of units per ml.

Histone and DNA detection in swollen spermatozoa and somatic cells, by immunofluorescence

A method of swelling spermatozoa and other cells, which leads to the exposure of nuclear antigens is described. By applying the indirect IFT on these swollen cells with sera containing antibodies to nuclear antigens, and by comparing the results to those obtained in other tests (measuring anti-nuclear antibodies), the following conclusions could be drawn: (a) By swelling human spermatoza, nuclear antigens of the sperm are exposed, and can be used for the detection of antibodies directed against them. (b) Heterlogous antibodies to histones F2al, FIa2 and F3 which can not be detected in the indirect IFT on rat liver cells, become detectable after swelling of these cells. (c) Mature human spermatozoa contain, in addition to double-stranded DNA and protamine, small amounts of histone F2b and F2a2. (d) In mature human spermatozoa histone F1 is absent.

Immunology of DNA. I. The influence of reaction conditions on the Farr assay as used for the detection of anti-ds DNA

The sensitivity and the specificity of the Farr assay for the detection of antibodies to double stranded (ds) DNA depends very much on the reaction conditions. The interaction between ds DNA and anti-ds DNA is inhibited when ionic strength and pH are increased. ds DNA is bound by normal sera at ionic strength lower than 0.11 M NaCl and at physiological ionic strength when the pH is lower than 7.2. Substantial binding of DNA by normal serum takes place in barbitone, borate or Tris-HCl buffers at concentrations of 30 mM or higher, even at a pH higher than 7.2. Such binding is due to Clq and is only partially prevented by heating the serum for 30 min at 56 degrees C, but 10 mM phosphate in the incubation mixture completely prevents it. Standardization of ionic strength, pH, phosphate concentration, incubation volume and DNA-serum ratio enhances the diagnostic usefulness of the Farr assay.

Immunology of DNA. III. Crithidia luciliae, a simple substrate for the determination of anti-dsDNA with the immunofluorescence technique

C. luciliae are hemoflagellates nonpathogenic for man and easy to culture. They have a giant mitochondrion, in which the mitochondrial DNA is concentrated in a single large network, the kinetoplast. When used as a substrate for the indirect immunofluorescence technique, studying sera from patients with SLE, we could demonstrate a very good correlation between this test and the Farr assay for the demonstration of antibodies to double-stranded DNA. Although the sensitivity of both techniques is on the same order of magnitude, the IF technique has the following advantages over the Farr assay. It is easy to perform in laboratories equipped for autoimmune serology. It possesses an intrinsic check on the immunoglobulin character of the DNA-binding activity. It allows one to determine the Ig classes and subclasses of antibodies to DNA. It permits study of complement fixation to antibodies without interference of Clq fixation to DNA or anticomplementarity of the serum. There is an absence of interference with antibodies to single-stranded DNA.