Insulin-like growth factor-I treatment reduces immune cell responses in acute non-demyelinative experimental autoimmune encephalomyelitis

To test the effects of insulin-like growth factor-I (IGF-I) on clinical deficits, lesion severity, and immune cell response in acute, non-demyelinative experimental autoimmune encephalomyelitis (EAE), we induced EAE in Lewis rats by passive transfer of an MBP-reactive T lymphocyte line. Four days after receiving 5 x 10(5) MBPL-1 T cells intravenously, ten pairs of rats had the same mild degree of tail and hind limb weakness. Ten were given 300 micrograms IGF-I i.v. twice daily for 6 days, and the other 10 received the same volume of 0.89% NaCl. Pairs of rats were sacrificed after 4 days and 6 days of IGF-I and placebo treatment and spinal cord sections were processed for immunostaining, in situ hybridization, and morphological examination. IGF-I treatment decreased clinical deficits, lesion numbers, and lesion areas significantly. Numbers of CD4-positive T cells, alpha/beta TCR-positive cells, and ED-1-positive macrophages were also significantly reduced by IGF-I treatment. Similar reductions were found in our second trial, when 11 days of placebo and IGF-I injections began the day after transfer. No demyelination was observed in either toluidine blue-stained semithin sections or sections immunostained with an antibody raised against myelin basic protein (MBP). We conclude that IGF-I-induced reductions in immune cell responses can occur in the absence of demyelination and are of major importance in decreasing clinical deficits and lesion severity in EAE. If IGF-I has similar effects in multiple sclerosis, we think that it will be useful therapeutically.