NOD FETAL THYMUS ORGAN-CULTURE - AN IN-VITRO MODEL FOR THE DEVELOPMENT OF T-CELLS INVOLVED IN IDDM

This paper introduces a model which incorporates fetal thymus organ cu lture (FTOC) from NOD mice to replicate thymic development of diabetog enic T cells. NOD fetal pancreas organ culture (FPOC) co-cultured with 13-16 day NOD FTOC for an additional 14-21 days produced less insulin than FPOC cultured alone. Insulin production from the FTOC of non-dia betic strains C57BL/6 and BALB/c was not inhibited by co-culture with FTOC from their syngeneic counterparts. Sections of the NOD co-culture s showed peri-islet infiltration with lymphocytes. Insulin reduction b y FTOC/FP co-culture was prevented by co-culture of the NOD FT with FT from immunologically incompetent C.B-17 SCID/SCID mice. Co-culture of NOD FP with NOD FT prior to the development of T cells prevented gene ration of diabetogenic FTOC. Thus, early exposure of NOD T cell precur sors to the thymic stromal elements of C.B-17 SCID/SCID FT or to islet antigens can negatively select for diabetogenic T cells or activate i mmune-regulatory cells that can suppress diabetogenic T cell activity. The addition of blocking F(ab')(2) fragments of anti-CD3 epsilon mono clonal antibody to NOD FTOC/FP co-cultures prevented insulin reduction , implicating a role for TcR-mediated recognition in this ''in vitro I DDM'' model. The addition of activating whole anti-CD3 epsilon caused the complete ablation of insulin production in FTOC/FP co-cultures fro m all strains tested. Transfer of unprimed syngeneic FTOC cells to pre diabetic NOD mice prevented the onset of IDDM while transfer of islet- cell primed FTOC/FP cells slightly increased disease incidence. These data suggest that while diabetogenic T cells are present in the FT, th ey are normally suppressed, even after organ culture. However, these c ells can induce the destruction of islet cells, in vitro and in vivo, if they are appropriately activated with pancreatic tissue. (C) 1997 A cademic Press Limited.