RETARDATION OR ACCELERATION OF DIABETES IN NOD LT MICE MEDIATED BY INTRATHYMIC ADMINISTRATION OF CANDIDATE BETA-CELL ANTIGENS/

A single injection of syngeneic islet cells into the thymus of 4-week- old NOD/Lt female mice strongly retards diabetogenesis. The present st udy used the intrathymic route of antigen administration to compare th e relative efficacy of peptides/proteins derived from two major candid ate pancreatic beta-cell autoantigens, insulin and GAD65, to modulate diabetogenesis. Intrathymic administration of insulin B chain or recom binant human GAD65 significantly suppressed diabetogenesis during a 20 -week follow-up period, whereas no protection was mediated by either i nsulin A chain or a synthetic peptide (A2) derived from it. Quite unex pectedly, two GAD65-derived peptides near the COOH-terminus (p34 and p 35) accelerated diabetes onset. Semiquantitative reverse transcription -polymerase chain reaction analysis aas performed on cDNAs from isolat ed islets or whole pancreases of NOD/Lt females 4 weeks after intrathy mic injections. Protection mediated by intrathymic administration with either intact islet cells or GAD65 were correlated with an upregulati on of mRNA for T-helper 2 (Th2)-associated cytokines (interleukin [IL] -4, IL-10), concomitant with downregulation of Th1-associated interfer on (IFN) transcripts (all normalized to T-cell receptor C beta transcr ipts) in islet-infiltrating lymphocytes. Protection mediated by the in trathymic administration of insulin B chain, however, correlated only with a modest upregulation of IL-4 and IL-10 transcript levels, and no diminution in IFN-gamma transcripts. In contrast, the diabetes-accele rating GAD65 p34 and p35 peptides were not associated with an immune d eviation, expressing levels of IFN-gamma characteristic of islet-infil trating lymphocytes in vehicle-injected NOD controls. Hence, Th1-to-Th 2 immune deviation provides only a partial explanation for peptide imm unotherapy of diabetes in NOD mice. The finding that certain peptides can accelerate rather than retard diabetogenesis as a function of rout e and age of administration adds a cautionary note to this type of the rapy.