Is quantitative assessment of insulin-antibodies and autoantibodies feasible?

A low level of naturally occurring antibodies associates with functional antibody deficiency

Functional antibody deficiency is clinically assessed from antibody responses to vaccination. However, diagnostic vaccination is complex and may fail in practice. We hypothesized that the levels of naturally occurring antibodies against galactose-α-1,3-galactose (αGal) may represent alternative markers of functional antibody capacity. We included data from 229 patients with suspected primary immunodeficiency in a retrospective study. Antibody levels against αGal and twelve pneumococcal serotypes were determined with solid-phase immunoassays. Pneumococcal vaccinations and treatment with normal human immunoglobulin were assessed from medical records. Anti-αGal antibody levels correlated positively with anti-pneumococcal antibody levels measured before and after pneumococcal vaccination. Contrary to the anti-pneumococcal antibody levels, the anti-αGal antibody level showed potential for predicting subsequent immunoglobulin treatment - a marker of disease severity. Naturally occurring antibodies may reflect the functional capacity tested by diagnostic vaccination but add more useful clinical data. The clinical utility of this easy test should be evaluated in prospective studies.

Comparison of antigenicity of Hoechst 21PH insulin using either implantable intraperitoneal pump or subcutaneous external pump infusion in type 1 diabetic patients

OBJECTIVE

To assess the antigenicity of the insulin Hoechst 21PH (Hoe21PH) using continuous subcutaneous insulin infusion (CSII) and to compare the antigenicity of this insulin when administered intraperitoneally or subcutaneously. RESEARCH DESIGN AND METHODS; Peritoneal administration of Hoe21PH (Hoechst-Roussel, Somerville, NJ) insulin using implantable devices (continuous peritoneal insulin infusion [CPII]) increases anti-insulin antibody (AIA) levels in type 1 diabetic patients. Intraperitoneal administration, addition of a stabilizer (polyethylene polypropylene glycol), or insulin modifications due to storage in the pump may be involved in this antigenicity. In this nonrandomized study, 24 type 1 diabetic patients were treated with either CSII (n = 11, group 1) or CPII (n = 13, group 2). AIA levels were measured by radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA) before starting patients on Hoe21PH and again after 3 and 6 months.

RESULTS

Patients were comparable in the two groups. AIA levels (RIA) remained stable (24.3 +/- 8.5% [month 0] to 24.9 +/- 8.5.5% [month 6]) in group 1 and increased (21.8 +/- 6.7% [month 0] to 41.8 +/- 6.9% [month 6]) in group 2 (P = 0.005, Wilcoxon's rank-sum test). Using ELISA, AIA remained stable in the patients in group 1 (n = 9; 3.8 +/- 0.8 units/ml [month 0] and 4.1 +/- 1.0 units/ml [month 6]) and tended to increase in the patients in group 2 (n = 12; 4.1 +/- 0.7 units/ml [month 0] to 17.5 +/- 4.6 units/ml [month 6]) (P = 0.07). Comparison of the evolution of AIA formation between the two groups, using RIA at months 0, 3, and 6 showed a significant difference (analysis of variance, P = 0.009).

CONCLUSIONS

No increase in AIA levels was demonstrated when Hoe21PH insulin was administered subcutaneously as assessed by two different assays. CPII is proven to be more antigenic than CSII, and this is not related to a specific antigenicity of Hoe21PH insulin. The intraperitoneal route of administration or insulin modifications due to insulin storage in implantable devices might explain this antigenicity.

Immunogenicity of intraperitoneal insulin infusion using programmable implantable devices

Intraperitoneal insulin infusion using implantable devices in insulin-dependent diabetic (IDDM) patients is promising since it improves diabetic control and decreases frequency of hypoglycaemia. However, preliminary data show a striking increase in plasma levels of anti-insulin antibodies with this therapy. In order to more precisely evaluate the immunogenicity and its consequences, anti-insulin antibody levels in 62 IDDM patients were assessed every 3 months during a 2-year period following pump implantation. At the same time, diabetes control was evaluated with HbA1c, mean blood glucose levels, standard deviation of the daily blood glucose levels and the frequency of low blood glucose (< 3.58 mmol/l). Factors involved in antibody formation such as age, gender, HLA typing, and complement C4 alleles were also studied. After implantation, anti-insulin antibody levels increased significantly from 3.14% (range 0-26%) to 8.34% (0-49%) after 1 year and remained elevated. Patients were divided into two groups: responders able to show at least one antiinsulin antibody titre higher than 15% and non-responders whose titres were always lower than 6%. None of the factors studied was shown to statistically influence the anti-insulin antibody titres. Non-responders had significantly better metabolic results than the responders. Severe hypoglycaemic episodes decreased dramatically in both groups. Insulin requirements were comparable at time 0 and decreased initially in both groups. They remained low for the non-responders but returned to pre-implantation values for responders. Intraperitoneal insulin infusion led to a high immunogenetic response towards insulin in about half of the patients, leading to only moderately deleterious effects on metabolic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoantibodies to endogenous growth hormone in short children (the Wessex Growth Study)

Small stature is associated with low growth hormone secretion, but in most cases the reason is unknown. The commonest cause of hormone insufficiency is autoimmunity, and autoantibodies to hormones are often found where there is autoimmune disease of the corresponding gland. Displaceable growth hormone binding by the sera of 125 short (< 3rd centile) but otherwise normal school entrants was significantly higher (P < 0.05) than by the sera of 100 age-matched children of normal height (10th-90th centile), and binding in 21 (17%) of the small children exceeded the upper limit of 95% of the normal population. Furthermore, urinary growth hormone excretion was significantly lower in the small children (total overnight output 0.6-1.7 ng) compared with controls (1.5-3.7 ng) (P < 0.05) even when corrected for body surface area. Thus, growth hormone binding and growth hormone excretion discriminated between two groups of children selected only on the basis of height. The assay used for growth hormone binding was specific for IgG, suggesting that the binding factor was antibody. Autoimmunity merits further investigation as a basis for poor growth.

Immunological resistance to human biosynthetic insulin--effects of immunosuppression and plasmapheresis

A 55-year-old gentleman, after being treated for a short time with a diet and with Chlorpropamide, was switched to purified porcine insulin due to ketonuria and ketoacidosis. After a year the patient developed immunological insulin resistance (mean daily insulin dose: 3.72 U/kg body weight; anti-insulin antibodies 78%). In order to lower anti-insulin antibodies human recombinant DNA insulin was introduced into further therapy. Contrary to expectations, the patient did not reduce whatsoever his anti-insulin antibodies and his daily insulin dose increased up to 5.63 U/kg body weight. Introduction of combined immunosuppressive therapy (prednisone plus azathioprine) together with plasmapheresis resulted in rapid lowering of daily insulin requirement and reduction in anti-insulin antibodies. Immunosuppressive therapy was continued with 10 mg of prednisone and a year later the patients insulin daily requirement was 0.66 U/kg BW while his antibodies were 18%. The possible causes of insulin resistance to human recombinant DNA insulin are discussed as well as the advantage of combined immunosuppressive therapy together with plasmapheresis that was used for rapid lowering of insulin daily requirement and anti-insulin antibodies titer.

Novel considerations on the antibody/autoantigen system in type I (insulin-dependent) diabetes mellitus

Insulin dependent diabetes (IDDM) has an autoimmune pathogenesis. Included is the presence of antibodies to pancreatic islet cells. The first identified were islet cell antibodies (ICA), detected by indirect immunofluorescence, and which react with all cells within islets. Importantly, the autoantibodies are found several years prior to disease and although a pathogenic role for the autoantibodies is unclear, they have become useful markers of prediabetes. A number of studies of twins discordant for IDDM and of first degree relatives of IDDM patients have established that there is an increased risk for disease in individuals who have ICA, especially when ICA levels are high. This high predictive value of ICA decreases in the general population where the incidence of IDDM is lower than in first degree relatives, and both ICA and the disease risk associated with ICA, appear to be influenced by a genetic susceptibility. This has been sustained in a study of patients with endocrine autoimmunity and ICA (Polyendocrine Study) where the predictive value of very high levels of ICA is less than 50% in patients without a first degree relative with IDDM. Hence, there remain a substantial number of patients with ICA who do not develop disease. From these patients, it was demonstrated that ICA include at least two distinct specificities, one of which is beta cell specific and is not associated with a high risk for IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of affinity of antibodies upon their detection by liquid phase radiobinding assay and solid phase enzyme linked immunosorbent assay. Demonstration using monoclonal antibodies raised against rDNA human proinsulin

Hybridomas producing proinsulin antibodies were cloned by limiting dilution of cell cultures obtained by fusion of splenocytes of immunized mice with immortal myeloma cells. Some proinsulin monoclonal antibodies crossreacted with labelled insulin but none did with labelled C-peptide indicating that the involved epitopes were at one of the insulin/C-peptide junctions or included in the insulin moiety. Hybridoma supernatants were assayed for IgG concentration by a solid phase assay and for ligand binding by a radiobinding assay and an enzyme linked immunosorbent assay. The half-life of immune complexes formed with radioligand was measured and, as expected, correlated with affinity as measured by the method of Scatchard. Antibody titres determined by enzyme linked immunosorbent assay did not correlate to those measured by radiobinding assay. IgG concentration correlated to enzyme linked immunosorbent assay titres but not to radiobinding assay titres. Finally, a significant correlation was found between radiobinding assay titre and the product of enzyme linked immunosorbent assay titre by the period of immune complexes. It is concluded that, except for very low affinity antibodies, enzyme linked immunosorbent assay is a capacity assay whereas radiobinding assay is influenced by both antibody concentration and affinity. The former assay is thus best suited to detecting low affinity antibodies whereas the latter is more efficient in the presence of low levels of high affinity antibodies.