Exploring the Pathogenic Role and Therapeutic Implications of Interleukin 2 in Autoimmune Hepatitis

Interleukin 2 is essential for the expansion of regulatory T cells, and low-dose recombinant interleukin 2 has improved the clinical manifestations of diverse autoimmune diseases in preliminary studies. The goals of this review are to describe the actions of interleukin 2 and its receptor, present preliminary experiences with low-dose interleukin 2 in the treatment of diverse autoimmune diseases, and evaluate its potential as a therapeutic intervention in autoimmune hepatitis. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Interleukin 2 is critical for the thymic selection, peripheral expansion, induction, and survival of regulatory T cells, and it is also a growth factor for activated T cells and natural killer cells. Interleukin 2 activates the signal transducer and activator of transcription 5 after binding with its trimeric receptor on regulatory T cells. Immune suppressor activity is increased; anti-inflammatory interleukin 10 is released; pro-inflammatory interferon-gamma is inhibited; and activation-induced apoptosis of CD8(+)T cells is upregulated. Preliminary experiences with cyclic injections of low-dose recombinant interleukin 2 in diverse autoimmune diseases have demonstrated increased numbers of circulating regulatory T cells, preserved regulatory function, improved clinical manifestations, and excellent tolerance. Similar improvements have been recognized in one of two patients with refractory autoimmune hepatitis. In conclusion, interferon 2 has biological actions that favor the immune suppressor functions of regulatory T cells, and low-dose regimens in preliminary studies encourage its rigorous investigation in autoimmune hepatitis.