Diabetes, Vol 44, Issue 11 1290-1295, Copyright © 1995 by American Diabetes Association
Pancreatic islet cell cytoplasmic antibody in diabetes is represented by antibodies to islet cell antigen 512 and glutamic acid decarboxylase
MA Myers, DU Rabin and MJ Rowley
Centre for Molecular Biology and Medicine, Monash University, Victoria, Australia.
The presence of serum islet cell cytoplasmic antibodies (ICAs) is a
standard autoimmune marker for insulin-dependent diabetes mellitus (IDDM).
The antigenic molecule(s) responsible for ICA has not been identified,
although antibodies to the 65-kDa isoform of glutamic acid decarboxylase
(GAD65) do contribute. We tested 129 IDDM sera for antibodies to ICA512
(anti-ICA512), antibodies to GAD (anti-GAD), and ICAs; we tested for
inhibition of ICAs with purified recombinant ICA512 and sheep brain GAD;
and we tested for immunofluorescence reactivity on COS7 cells transfected
with cDNA clones encoding ICA512 and GAD65. The results were that
anti-ICA512 antibodies contribute to ICA reactivity and that these, in
combination with anti-GAD antibodies, account for most ICA reactivity in
IDDM. Anti-ICA512 antibodies were present at a frequency of 51% in 61
patients with early-onset IDDM (age of onset < or = 20 years) of short
duration (< or = 1 month) but only in 9% of 68 patients with an onset
age of > 20 years and/or a disease duration of > 1 month. The
frequency of anti-GAD antibodies in these sera was similar irrespective of
duration or age of onset. Anti-ICA512 and anti-GAD antibodies were
demonstrable by indirect immunofluorescence on transfected COS7 cells, and
ICA could be inhibited using either recombinant ICA512 or purified brain
GAD. We conclude that anti-ICA512 and anti-GAD antibodies contribute to ICA
reactivity and that anti-ICA512 antibodies account for the increased
frequency of ICA reactivity in early-onset IDDM of short duration.