PROTECTION AGAINST AUTOIMMUNE DIABETES WITH ORAL INSULIN IS ASSOCIATED WITH THE PRESENCE OF IL-4 TYPE-2 T-CELLS IN THE PANCREAS AND PANCREATIC LYMPH-NODES

Oral administration of antigens has been proposed in the prevention an d treatment of autoimmune diseases. We reported that oral administrati on of 0.8 mg of recombinant human insulin to 6-week-old NOD mice every other day for a month generated regulatory T-cells that were able to reduce the severity of insulitis and the percentage of clinical diabet es in naive irradiated recipients when co-injected with diabetogenic T -cells. In the present study, immunohistochemical analysis of the panc reatic glands revealed that injection of T-cells from insulin-fed mice upregulated the number of interleukin (IL)-4-secreting cells within t he islets. Using two strains of NOD mice congenic at the Theta, or Thy 1, locus, we observed a higher proportion of T-cells from insulin-fed mice in both the spleen (7.73 +/- 0.3 vs. 5.57 +/- 0.2%; P < 0.001) an d the pancreatic lymph nodes (10.1 +/- 0.8 vs. 7.2 +/- 0.7%; P < 0.05) of cotransferred mice. By reverse transcription-polymerase chain reac tion (RT-PCR) analysis, mice reconstituted with T-cells from insulin-f ed animals had detectable amounts of IL-4 mRNA, specifically in the pa ncreatic lymph nodes (8 of 9 experimental mice vs. 1 of 9 control mice ) and the pancreas (3 of 3 experimental mice vs. 0 of 3 control mice). gamma-Interferon mRNA was detectable in all cotransferred animals, bu t IL-10 mRNA and transforming growth factor beta mRNA were undetectabl e. These results suggested a shift from a T-helper 1 (Th1) to a Th2 pa ttern of cytokine expression and underlined the role of pancreatic lym ph nodes in the protection. Repeated injections of 500 mu g s.c. of an ti-IL-4 monoclonal antibody led to an accentuation of the severity of islet infiltration and to the development of clinical diabetes. We con cluded that oral administration of insulin can induce the presence of regulatory T-cells in the pancreas and the corresponding draining lymp h nodes, initiate the secretion of IL-4 in this microenvironment suffi ciently to suppress the activity of Th1 autoreactive T-cell clones, an d ultimately provide protection against autoimmune diabetes.