Factors affecting the insulin autoantibody ELISA

Anti-protamine-heparin antibodies: incidence, clinical relevance, and pathogenesis

Protamine, which is routinely used after cardiac surgery to reverse the anticoagulant effects of heparin, is known to be immunogenic. Observing patients with an otherwise unexplained rapid decrease in platelet count directly after protamine administration, we determined the incidence and clinical relevance of protamine-reactive antibodies in patients undergoing cardiac-surgery. In vitro, these antibodies activated washed platelets in a FcγRIIa-dependent fashion. Using a nonobese diabetic/severe combined immunodeficiency mouse model, those antibodies induced thrombocytopenia only when protamine and heparin were present but not with protamine alone. Of 591 patients undergoing cardiopulmonary bypass surgery, 57 (9.6%) tested positive for anti-protamine-heparin antibodies at baseline and 154 (26.6%) tested positive at day 10. Diabetes was identified as a risk factor for the development of anti-protamine-heparin antibodies. In the majority of the patients, these antibodies were transient and titers decreased substantially after 4 months (P < .001). Seven patients had platelet-activating, anti-protamine-heparin antibodies at baseline and showed a greater and more prolonged decline in platelet counts compared with antibody-negative patients (P = .003). In addition, 2 of those patients experienced early arterial thromboembolic complications vs 9 of 584 control patients (multivariate analysis: odds ratio, 21.58; 95% confidence interval, 2.90-160.89; P = .003). Platelet-activating anti-protamine-heparin antibodies show several similarities with anti-platelet factor 4-heparin antibodies and are a potential risk factor for early postoperative thrombosis.

Therapeutic targeting of Syk in autoimmune diabetes

In APCs, the protein tyrosine kinase Syk is required for signaling of several immunoreceptors, including the BCR and FcR. We show that conditional ablation of the syk gene in dendritic cells (DCs) abrogates FcgammaR-mediated cross priming of diabetogenic T cells in RIP-mOVA mice, a situation phenocopied in wild-type RIP-mOVA mice treated with the selective Syk inhibitor R788. In addition to blocking FcgammaR-mediated events, R788 also blocked BCR-mediated Ag presentation, thus broadly interrupting the humoral contributions to T cell-driven autoimmunity. Indeed, oral administration of R788 significantly delayed spontaneous diabetes onset in NOD mice and successfully delayed progression of early-established diabetes even when treatment was initiated after the development of glucose intolerance. At the DC level, R788 treatment was associated with reduced insulin-specific CD8 priming and decreased DC numbers. At the B cell level, R788 reduced total B cell numbers and total Ig concentrations. Interestingly, R788 increased the number of IL-10-producing B cells, thus inducing a tolerogenic B cell population with immunomodulatory activity. Taken together, we show by genetic and pharmacologic approaches that Syk in APCs is an attractive target in T cell-mediated autoimmune diseases such as type 1 diabetes.

Identification of natural antibodies to interleukin-18 in the sera of normal humans and three nonhuman primate species

Natural antibodies to cytokines can be found in the sera of normal healthy individuals in the absence of specific immunostimulation. However, the function, impact, and purpose of natural antibody development have yet to be fully elucidated. Interleukin (IL)-18 is a cytokine that exerts proinflammatory activities and induces natural killer (NK) cell activity. Recombinant human IL-18 (rHuIL-18) is currently in development as a cancer immunotherapy. In this study, the presence of natural antibodies to IL-18 in the sera of normal humans and three nonhuman primate species was evaluated by electrochemiluminescence immunoassay (ECLIA). Of the human sera tested, 6 of 47 samples were positive for natural antibodies to IL-18. Of the nonhuman primate sera tested, 22 of 80 cynomolgus monkey samples, 4 of 31 rhesus monkey samples, and 2 of 20 chimpanzee samples were positive for natural antibodies to IL-18. Natural anti-IL-18 antibodies were neutralizing in 5 of 22 cynomolgus and 2 of 4 rhesus sera. None of the chimpanzee or human sera were able to neutralize IL-18 induction of interferon (IFN)-gamma in vitro. In vivo activity of rHuIL-18 was compared in IL-18 natural antibody-positive and -negative cynomolgus monkeys. The presence of natural antibodies to IL-18 did not alter rHuIL-18 systemic exposure levels, induction of neopterin, or induction of treatment-induced antibodies following intravenous administration of rHuIL-18. In conclusion, our data indicate that, as has been found with other cytokines, natural anti-IL-18 antibodies are relatively common. Moreover, natural anti-IL-18 antibodies do not appear to influence rHuIL-18 activity in vivo and are not predictive of a heightened immune response, suggesting that natural anti-IL-18 antibodies do not impact IL-18 therapy. Finally, our data suggest that the ability to detect natural anti-cytokine antibodies may be a useful measure of the adequacy of an assay for deployment in clinical trials.

Anti-insulin antibodies and the natural autoimmune response in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by the finding of ample serum autoantibodies. The role and the origin of many of these antibodies are still obscure. The aim of this work was to study the occurrence of anti-insulin antibodies (AIA) in SLE, and to postulate, based on AIA determination, on the mechanisms involved in the production of some autoantibodies in SLE. IgG and lgM AIA, anti-DNA antibodies (ADA) and anti-tetanus toxoid antibodies (ATA) were determined using ELISA in sera and B-lymphocytes culture media of 24 SLE patients, 10 healthy controls and 19 insulin-dependent diabetes mellitus (IDDM) patients. B- and T-lymphocytes were isolated using Ficoll gradient, depleted of T-cells using cyclosporin A, EBV infected and grown in medium. The frequencies of IgM-AIA and IgG-ADA were higher in SLE patients than in healthy controls (P < 0.02 and P < 0.05, respectively). The rate of IgM-AIA in SLE and IDDM was comparable, while IgG-AIA was significantly less common in SLE than in IDDM (P < 0.05). The prevalence of ATA in SLE patients and healthy controls was similar. These findings increase the spectrum of the humoral autoimmune response in SLE and suggest that part of it (natural autoantibodies) is independent of antigen driven response.

Preference for IgG mAb binding insulin in solution or on surfaces is related to immunoglobulin variable region structures

Studies on insulin autoantibodies often show a lack of correlation between enzyme-linked immunosorbent assays (ELISAs) and fluid phase radioimmunoassays (RIAs). Similarly, a set of IgG anti-insulin monoclonal antibodies (mAb) from BALB/c mice are found to differ in their binding in ELISAs and RIAs. To understand the structural basis for differential insulin binding, soluble and complexed biotinylated insulin is used to confirm binding properties independent of insulin-coated plastic and radioiodination. The binding properties of intact mAb are also present in Fab fragments, indicating ligand preference is not related to valence or to the Fc portion of Ig. Analysis of binding to soluble or bound ligand in relationship to antibody variable (V) region structures indicates that differential binding in the two assays is a property of heavy chain variable region structure. Studies also show that limited amino acid replacements arising during maturation of the immune response may change the binding preference for an individual mAb. These findings indicate that differences in detection of insulin binding in solid phase and fluid phase are not artefactual but reflect intrinsic structural features of immunoglobulin interaction with insulin.

Protamine antibody production in diabetic subjects treated with NPH insulin

Treatment with neutral protamine Hagedorn (NPH) insulin predisposes individuals with diabetes to anaphylactoid reactions when given bolus protamine for heparin reversal during cardiovascular procedures. To prospectively examine production of protamine antibodies, 30 patients with non-insulin dependent diabetes were followed for 12 months from initiation of therapy with porcine NPH or Lente insulin. Twenty-one subjects were randomly assigned to NPH (protamine containing) and nine controls to Lente (protamine free) insulin. Protamine specific IgG antibody was produced by 6/21 (29%) of NPH-treated subjects and 0/9 controls. Among NPH treated subjects, there was no difference between protamine antibody producers and non-producers with regard to age, race, weight, or pre-treatment glycosylated hemoglobin. Both producer and non-producer groups received similar amounts of insulin and protamine and achieved similar glycemic control. Insulin antibodies were made by 4/6 (67%) of protamine antibody producers and by 6/15 (40%) of non-producers (NS). The authors conclude that one of three new diabetics who are treated with porcine NPH insulin will make IgG protamine antibodies. These antibodies do not affect insulin requirements, glycemic control, or insulin antibody production. Because of the frequency of protamine antibody production and the risk of anaphylaxis to bolus protamine administration in NPH treated diabetics, the authors suggest that NPH insulin-treated individuals should avoid heparin reversal by protamine.