Presence of anti-insulin reaginic auto-antibodies of the IgG4 class in insulin-dependent (type I) diabetic patients before insulin therapy.

The autoimmune aetiology of type I diabetes has been well documented. We studied whether anti-insulin anaphylactic antibodies were present on the membrane of basophils from type I diabetics by the toluidine blue method (detecting basophil activation after stimulation by insulin). We observed that basophils of recently diagnosed insulin-dependent diabetic patients (n = 13) were statistically more frequently activated by insulin than basophils from noninsulin-dependent diabetics (p < 0.002, n = 8) or non-diabetic subjects (p < 0.05, n = 9). Basophils from normal donors were passively sensitized with plasma from insulin-dependent diabetics and could then be activated by insulin. This sensitization still occurred when using plasma previously heated to 56 degrees C, indicating that the sensitizing antibodies were not of the IgE class. When basophils from type I diabetics were preincubated with anti-IgG subclasses, only anti-IgG4 monoclonal antibodies inhibited the insulin-induced basophil activation. By contrast, preincubation with blocking concentrations of anti-IgG1-3 antibodies or desensitization of the IgE pathway did not modify basophil activation. These experiments strongly suggest the presence of anti-insulin antibodies of the IgG4 subclass in insulin-dependent diabetics before any insulin administration and provide a simple tool to complement the usual method of detecting auto-antibodies in diabetes.

Regulation of human basophil activation. I. Dissociation of cationic dye binding from histamine release in activated human basophils.

Human basophil activation was demonstrated by histamine release (HR) and by the decrease of the toluidine blue-positive basophils (TB+). In four experimental systems, TB+ number decreased in the absence of HR (1) in basophils from atopic subjects stimulated by allergen concentrations below the threshold for HR, (2) in basophils sensitized by anti-2,4-dinitrophenyl IgE stimulated by noncovalently linked 2,4-dinitrobenzene sulfonic acid-human serum albumin (also, the threshold for decrease of TB+ required lower concentrations of sensitizing anti-2,4-dinitrophenyl IgE than for HR), (3) in low Ca++ medium, and (4) in the presence of the Na+/H+ exchanger, monensin. These results suggest that (1) there is a lower threshold for TB+ decrease than for HR in allergen concentration, number of membrane IgE molecules, and number of IgE cross-linkings; moreover, external Ca++ requirement is lower for decrease of TB+ than for HR and (2) TB+ decrease reflects either granule exocytosis or, in the absence of HR, biochemical changes (most probably cation exchanges) altering the interaction of the basic dye with the granules. Thus, monitoring decrease in TB+ allows detection of basophil activation in the absence of HR.