Cytotoxic Autoantibodies to Beta Cells in the Serum of Patients with Insulin-Dependent Diabetes Mellitus

Abstract

We studied serum from 36 patients with insulin-dependent diabetes mellitus (IDDM) for the capacity to lyse beta cells. Immunofluorescence revealed an islet-cell cytoplasmic antibody (ICA) in 20 patients with IDDM and an islet-cell-surface antibody (ICSA) in 23. Neither ICA nor ICSA was found in any of 21 normal controls or 15 patients with non-insulin-dependent diabetes. In the presence of complement. ICSA-positive serum caused significant lysis as measured by release of 51Cr (50.1 +/- 8.8 per cent) from cultured rat islet cells, but ICSA-negative serum did not (17.7 +/- 7.3 per cent) (P < 0.001). Proof that ICSA-positive serum was lytic for beta cells was obtained by a double-fluorescence technique that identified lysed cells by their capacity to take up ethidium bromide and beta cells by their staining with fluorescein-conjugated antibody to insulin. These findings suggest that cytotoxic ICSA contributes to the pathogenesis of IDDM, but the mere presence of ICSA does not appear to be sufficient to produce diabetes; family studies showed that one fourth of the serum samples from nondiabetic first-degree relatives of diabetic probands were ICSA-positive and cytotoxic for beta cells.

Evidence for enhanced rates of complement activation in serum from patients with newly diagnosed insulin-dependent diabetes mellitus exposed to rat islet cells and complement-dependent induction of islet cell apoptosis

“…However, the IDDM patients used in the latter study had been diagnosed some years earlier (mean 3 years, range 2-23 years), thus it is probable that reduced circulating autoantibody and activated complement components in these patients may explain the low levels reported (Bergamaschini et al 1991) compared with those reported here for newly diagnosed patients. Other reports have shown that complement-fixing islet cell antibodies are increased in the serum of IDDM individuals (Bonifacio et al 1995, Dobersen et al 1980. The previous studies may have been unable to detect significant levels of activated complement in serum from IDDM patients, because of lack of availablity or poor specificity of antibodies used for the TCC ELISA.…”

Islet cell antibodies ? Theoretical and practical implications

“…The presence of islet cell surface antibodies capable of mediating a complement-dependent cytotoxic reaction does not necessarily imply that these antibodies are actively 'diabetogenic' since they have been found in a large proportion of first degree relatives of diabetic probands [18]. The various approaches to islet cell antibody determination and the different characters of the tissue preparations may be taken as an argument that islet cell antibodies are directed against several different antigens.…”

Immune islet killing mechanisms associated with insulin-dependent diabetes: Three rabbit antibody-mediated islet cell cytotoxicity models

“…Most reports are of indirect observations, but recent studies have attempted to associate immune mechanisms to human diabetes using complement-dependent antibody-mediated cytotoxicity (C'AMC) assays [3][4][5][6][7]. Cytotoxicity assays in vitro and the reported results vary, but each method described uses islet derived target cells.…”

“…Cytotoxicity assays in vitro and the reported results vary, but each method described uses islet derived target cells. One report suggests that virtually all sera from Type 1 diabetic patients have C'AMC against cultured rat islet cells, and that sera from non-diabetic parents and siblings also mediated C'AMC [6]. Using intact normal rodent islets or rat or human islet turnout target cells, 10%-30% of patients' sera have C'AMC [3][4][5]7].…”