Cytoplasmic islet cell antibodies and endogenous insulin secretion were studied in 184 children and adolescents having insulin-dependent diabetes mellitus (IDDM) in a cross-sectional study. The mean age of the subjects was 12.3 yr (range: 2.8–19.2 yr), and the mear duration of diabetes was 4.6 yr (range: 0.1–15.6 yr). Islet cell antibodies (ICA) were determined by both the indirect immunofluorescence (IF-ICA) and the complement-fixing (CF-ICA) methods. Forty-four patients (23.9%) were positive with respect to both IF- and CF-ICA, 54 patients (29.3%) had only IF-ICA, and 86 patients had no ICA. The patients having CF-ICA had a significantly higher endogenous insulin secretion in comparison with the patients who were only IF-ICA positive. The difference between the groups remained significant even when the age at onset of diabetes and the duration of the disease weretaken into account.

This finding, revealing an association between CF-ICA and endogenous insulin secretion, suggests that complement-fixing antibodies are seen only if the beta-cell mass is sufficiently preserved. The result contradicts the hypothesis, based on studies in vitro, that CF-ICA should be involved in the selective beta-cell damage in IDDM.

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