We studied a patient with
systemic lupus erythematosus and type
B insulin resistance who showed almost complete normalization of postprandial plasma
glucose in 3 months and a transient occurrence of
fasting hypoglycemia from day 35 (i.e. the 35th day of hospitalization) to day 77. To determine the clinical relevance of the
biological ability of anti-
insulin receptor antibodies (anti-IRAb), we made multiple preparations of the patient's dialyzed serum and
IgG. Dialyzed serum prepared on day 1 showed 95% inhibition of
insulin binding. The binding inhibition was, however, decreased parallel to the normalization of
insulin sensitivity. For 2DG uptake, 6.2 microM
IgG purified on 3 different days (days 7, 35 and 78, designated
IgG-NOV, -JAN, and -FEB, respectively) stimulated 2DG uptake into CHO-hIR at 3.4-, 3.1-, and 1.5-fold, respectively.
Phosphotyrosine immunoblotting revealed that apparent
insulin receptor autophosphorylation was visible only with
IgG-NOV, not with the
IgG-JAN or -FEB. Mutation of tyrosine-960 or lysine-1018 of the
insulin receptor failed to transduce the
IgG's stimulatory effect.
IgG-NOV was not able to stimulate the autophosphorylation of the human
IGF-I receptor. In the present study, the
insulin binding inhibitory activities of the dialyzed sera prepared at different time points were shown to be altered parallel to
insulin sensitivity in vivo. Stimulatory activities of the patient's
IgG were, however, discordant for the occurrence of
fasting hypoglycemia observed in vivo. Other pathogenic factors or mechanisms in addition to the
insulin-like action of the anti-IRAb may be also required to fully understand the development of
fasting hypoglycemia in type
B insulin resistance.